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Strontium-substituted hydroxyapatite coatings deposited via a co-deposition sputter technique
Abstract
The bioactivity of hydroxyapatite (HA) coatings can be modified by the addition of different ions, such as silicon (Si), lithium (Li), magnesium (Mg), zinc (Zn) or strontium (Sr) into the HA lattice. Of the ions listed here, strontium substituted hydroxyapatite (SrHA) coatings have received a lot of interest recently as Sr has been shown to promote osteoblast proliferation and differentiation, and reduce osteodast activity. In this study, SrHA coatings were deposited onto titanium substrates using radio frequency (RF) magnetron co-sputtering (and compared to those surfaces deposited from HA alone). FTIR, XPS, XRD, and SEM techniques were used to analyse the different coatings produced, whereby different combinations of pure HA and 13% Sr-substituted HA targets were investigated. The results highlight that Sr could be successfully incorporated into the HA lattice to form SrHA coatings. It was observed that as the number of SrHA sputtering targets in the study were increased (increasing Sr content), the deposition rate decreased. It was also shown that as the Sr content of the coatings increased, so did the degree of preferred 002 orientation of the coating (along with obvious changes in the surface morphology). This study has shown that RF magnetron sputtering (specifically co-sputtering), offers an appropriate methodology to control the surface properties of Sr-substituted HA, such as the crystallinity, stoichiometry, phase purity and surface morphology.
... In order to increase metal and/or alloy corrosion resistance, a protective coating can be applied using a range of techniques including plasma spraying [15,16], sol gel [17][18][19], micro arc oxidation technology [20][21][22] and RF magnetron sputtering [23][24][25][26]. In the case of a normal orthopaedic implant device, barrier layers can be used to negate any interaction between the underlying Mg and body fluids [6,27] whereby Cl − ions will actively promote degradation. ...
... Previous studies have shown that such sputter deposited CaP coatings can delay corrosion of Mg alloys while still undergoing dissolution [38]. The use of substituted hydroxyapatite systems, including those with single and multiple ions such as zinc (Zn 2+ ), fluoride (F − ), silver (Ag + ) and strontium (Sr 2+ ) [26,[39][40][41] replacing calcium (Ca 2+ ) in the HA lattice, offers the potential to create coatings that can both control Mg alloy corrosion and attendant enhanced bioactivity with the potential for conferring an osteoinductive response. Strontium plays an important role in bone formation, with Sr 2+ ions stimulating osteoblastic cell proliferation and differentiation [42][43][44]. ...
... A ramp up power of 1 W/s was used for CaP targets, however, due to the fragile nature of the SrCaP target the ramp up power was reduced to 0.2 W/s, to prevent surface cracking. RF magnetron sputtering was undertaken using dry pressed powder targets for a period of 30 h using the conditions provided in Table 2. Thin film CaP coating thickness has been related to sputtering parameters on a range of substrates [24,26,34,36]. More specifically, on magnesium, the parameters used in Table 2 are known to yield a CaP and SrCaP coating thickness of ~340 nm based on previous studies of the relationship between film thickness and sputter time, carried out using ToF-SIMS depth profiling and contact profilometry [25]. ...
Magnesium (Mg) alloys have significant potential for use as bioresorbable orthopaedic implant devices due to their controllable mechanical properties and an ability to promote new bone growth. However, difficulty lies with controlling the rate of corrosion in physiological conditions to ensure the load-bearing capability of the device is maintained for the required period of time, specifically until an adequate quantity of new bone tissue is formed. In this work, RF magnetron sputtering has been used to create calcium phosphate (CaP) and strontium-substituted calcium phosphate (SrCaP) thin film coatings on two Mg alloy systems (denoted WJK and ZEWX) that have been formulated for the fabrication of orthopaedic fracture fixation devices. A 14-day static-dynamic immersion study in simulated body fluid (SBF), shows that uncoated WJK substrates had a corrosion rate of 4.04 ± 0.15 millimetres per year (mmpy), which was reduced to 3.22 ± 0.17 mmpy with the application of a CaP coating, and to 2.92 ± 0.05 mmpy with a SrCaP coating. Uncoated ZEWX substrates had a corrosion rate of 3.36 ± 0.05 mmpy which was reduced to 2.98 ± 0.19 mmpy and 2.79 ± 0.03 mmpy, for CaP and SrCaP coatings, respectively. Whereas the sputter-deposited CaP and SrCaP coatings completely dissolve in SBF over the period of immersion, their presence at the outset significantly decreases the corrosion rate of both Mg alloys, as compared to the values for the uncoated substrates. Successful incorporation of Sr within the coating offers the potential for improved bioactivity with respect to directing the bone cell response to create new tissue.
... The XRD patterns of the HA and HA@Ag nanoparticles were detected, as shown in Figure 1c. Evidently, three typical characteristic peaks located at 25.9°, 31.9°, and 46.7° appeared on the HA patterns, which corresponded to its (002), (211), and (222) planes, respectively [36,37]. As for HA@Ag, three remarkable peaks located at 38.1°, 44.2°, and 64.5° were The XRD patterns of the HA and HA@Ag nanoparticles were detected, as shown in Figure 1c. ...
... As for HA@Ag, three remarkable peaks located at 38.1°, 44.2°, and 64.5° were The XRD patterns of the HA and HA@Ag nanoparticles were detected, as shown in Figure 1c. Evidently, three typical characteristic peaks located at 25.9 • , 31.9 • , and 46.7 • appeared on the HA patterns, which corresponded to its (002), (211), and (222) planes, respectively [36,37]. As for HA@Ag, three remarkable peaks located at 38.1 • , 44.2 • , and 64.5 • were observed, which were ascribed to the (111), (200), and (220) of planes of Ag, respectively [38]. ...
The integration of hydroxyapatite (HA) with broad-spectrum bactericidal nano-silver within biopolymer-based bone scaffolds not only promotes new bone growth, but also effectively prevents bacterial infections. However, there are problems such as a poor interface compatibility and easy agglomeration. In this project, zeolitic imidazolate frameworks (ZIF-8) were grown in situ on nano-HA to construct a core–shell structure, and silver was loaded into the ZIF-8 shell through ion exchange. Finally, the core–shell structure (HA@Ag) was composited with polylactic acid (PLLA) to prepare bone scaffolds. In this case, the metal zinc ions of ZIF-8 could form ionic bonds with the phosphate groups of HA by replacing calcium ions, and the imidazole ligands of ZIF-8 could form hydrogen bonds with the carboxyl groups of the PLLA, thus enhancing the interface compatibility between the biopolymers and ceramics. Additionally, the frame structure of MOFs enabled controlling the release of silver ions to achieve a long-term antibacterial performance. The test results showed that the HA@Ag nanoparticles endowed the scaffold with good antibacterial and osteogenic activity. Significantly, the HA@Ag naoaprticle exhibited a good interfacial compatibility with the PLLA matrix and could be relatively evenly dispersed within the matrix. Moreover, the HA@ZIF-8 also effectively enhanced the mechanical strength and degradation rate of the PLLA scaffold.
... Compared to the XRD pattern of pure nHAp, the peak positions of Sr-doped nHAp were shifted slightly to lower 2θ values and showed broadening (Figure 1a). XRD peaks for metal-doped hydroxyapatite showed broadened peaks with a shift to lower 2θ values, indicating decreased crystallinity of the samples and effective replacement of calcium by larger ions within the nHAp lattice [43]. A broadened peak with a small switch to greater 2θ values was observed for the Zn-4-nHAp, as shown in Figure 1b. ...
... The incorporation of Sr in the HA lattice was evidenced by a shift to slightly lower wavenumbers as well as peak broadening for the (PO4) 3− peaks [54]. An increase in both (HPO4) 2− and (CO3) 2− resulted from the substitution of Sr for Ca in the HAp lattice due to the augmented lattice strain initiated by the larger ions of Sr [43]. ...
Synthetic bone graft substitutes have attracted increasing attention in tissue engineering.
This study aimed to fabricate a novel, bioactive, porous scaffold that can be used as a bone substitute. Strontium and zinc doped nano-hydroxyapatite (Sr/Zn n-HAp) were synthesized by a waterbased sol-gel technique. Sr/Zn n-HAp and poly (lactide-co-glycolide) (PLGA) were used to fabricate
composite scaffolds by supercritical carbon dioxide technique. FTIR, XRD, TEM, SEM, and TGA
were used to characterize Sr/Zn n-HAp and the composite scaffolds. The synthesized scaffolds were
adequately porous with an average pore size range between 189 to 406 µm. The scaffolds
demonstrated bioactive behavior by forming crystals when immersed in the simulated body
fluid. The scaffolds after immersing in Tris/HCl buffer increased the pH value of the medium, establishing their favorable biodegradable behavior. ICP-MS study for the scaffolds detected the presence of Sr, Ca, and Zn ions in the SBF within the first week, which would augment osseointegration if implanted in the body. nHAp and their composites (PLGA-nHAp) showed ultimate compressive strength ranging between 0.4–19.8 MPa. A 2.5% Sr/Zn substituted nHAp-PLGA composite showed a compressive behavior resembling that of cancellous bone indicating it as a good candidate for cancellous bone substitute.
... Coated substrates were placed into two groups of equal number; with the first set left in the as-deposited state (TI-HA-AD) while the second were placed on a high temperature ceramic tray and inserted into a furnace (AWF 12/ 5, Lenton 3216 furnace, Lenton, UK) to be annealed at 500°C (at a heating rate of 10°C per min) for 4 h [13,14]. Annealing of the as-deposited coatings on the Ti substrates (TI-HA-AD) resulted in coating re-crystallisation (TI-HA-ANN). ...
... Annealing of the as-deposited coatings on the Ti substrates (TI-HA-AD) resulted in coating re-crystallisation (TI-HA-ANN). The sputtering and thermal annealing techniques described are well-established and proven in-house methods for preparing homogenous as-deposited HA-like thin film coatings and re-crystalised HA-like thin film coatings, respectively, on Ti and other substrates [14][15][16][17]. ...
There is continued focus on the development of new biomaterials and associated biological testing methods needed to reduce the time taken for their entry to clinical use. The application of Raman spectroscopy to the study of individual cells that have been in contact with biomaterials offers enhanced in vitro information in a potentially non-destructive testing regime. The work presented here reports the Raman spectral analysis of discreet U-2 OS bone cells after exposure to hydroxyapatite (HA) coated titanium (Ti) substrates in both the as-deposited and thermally annealed states. These data show that cells that were in contact with the bioactive HA surface for 7 days had spectral markers similar to those cultured on the Ti substrate control for the same period. However, the spectral features for those cells that were in contact with the annealed HA surface had indicators of significant differentiation at day 21 while cells on the as-deposited surface did not show these Raman changes until day 28. The cells adhered to pristine Ti control surface showed no spectral changes at any of the timepoints studied. The validity of these spectroscopic results has been confirmed using data from standard in vitro cell viability, adhesion, and proliferation assays over the same 28-day culture period. In this case, cell maturation was evidenced by the formation of natural bone apatite, which precipitated intracellularly for cells exposed to both types of HA-coated Ti at 21 and 28 days, respectively. The properties of the intracellular apatite were markedly different from that of the synthetic HA used to coat the Ti substrate with an average particle size of 230 nm, a crystalline-like shape and Ca/P ratio of 1.63 ± 0.5 as determined by SEM-EDX analysis. By comparison, the synthetic HA particles used as a control had an average size of 372 nm and were more-rounded in shape with a Ca/P ratio of 0.8 by XPS analysis and 1.28 by SEM-EDX analysis. This study shows that Raman spectroscopy can be employed to monitor single U-2 OS cell response to biomaterials that promote cell maturation towards de novo bone thereby offering a label-free in vitro testing method that allows for non-destructive analyses.
... The peak at 631 cm −1 in HA was due to librational mode, ν L , of the hydroxyl group [30]. This peak was absent in Se-HA and Se-Sr-HA, as reported by Boyd et al., due to the replacement of carbonate at OH − sites [31]. In HA, the small band at 1405 cm −1 was characteristic of the stretching mode (ν 3 ) in CO 3 2− . ...
... The peak at 631 cm −1 in HA was due to librational mode, νL, of the hydroxyl group [30]. This peak was absent in Se-HA and Se-Sr-HA, as reported by Boyd et al., due to the replacement of carbonate at OH − sites [31]. In HA, the small band at 1405 cm −1 was characteristic of the stretching mode (ν3) in CO3 2− . ...
In this study, as a measure to enhance the antimicrobial activity of biomaterials, the selenium ions have been substituted into hydroxyapatite (HA) at different concentration levels. To balance the potential cytotoxic effects of selenite ions (SeO32−) in HA, strontium (Sr2+) was co-substituted at the same concentration. Selenium and strontium-substituted hydroxyapatites (Se-Sr-HA) at equal molar ratios of x Se/(Se + P) and x Sr/(Sr + Ca) at (x = 0, 0.01, 0.03, 0.05, 0.1, and 0.2) were synthesized via the wet precipitation route and sintered at 900 °C. The effect of the two-ion concentration on morphology, surface charge, composition, antibacterial ability, and cell viability were studied. X-ray diffraction verified the phase purity and confirmed the substitution of selenium and strontium ions. Acellular in vitro bioactivity tests revealed that Se-Sr-HA was highly bioactive compared to pure HA. Se-Sr-HA samples showed excellent antibacterial activity against both Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus carnosus) bacterial strains. In vitro cell–material interaction, using human osteosarcoma cells MG-63 studied by WST-8 assay, showed that Se-HA has a cytotoxic effect; however, the co-substitution of strontium in Se-HA offsets the negative impact of selenium and enhanced the biological properties of HA. Hence, the prepared samples are a suitable choice for antibacterial coatings and bone filler applications.
... Fabrication technologies that are widely used to produce porous polymer coating on implants are sol-gel (Catauro et al., 2014), dip coating (Catauro et al., 2017), electrospinning (Kohse et al., 2018), electrophoretic deposition (Razavi et al., 2015), laser spallation (Karthika et al., 2015), sputter coating (Boyd et al., 2015), and spray coating (Schlaich et al., 2018) techniques. Recently, electrospinning nanofibres have been extensively investigated for the fabrication of composite nanofibres, which contain bioactive molecules to meet bone tissue requirements . ...
... Ca/Pbased coatings, such as HAp and tricalcium phosphate (TCP), are recognized for their high bioactivity and, as a result, their potential to stimulate bone regeneration [36]. Because of its comparable shape and composition to the mineral phase of bone, HAp has been widely recognized as a viable option for covering metallic implants [37]. ...
A researcher needs to know all the chemical, physical, biological, structural, and
mechanical characteristics of a biomedical material before using it in medical
applications. The mineral hydroxyapatite (HAp, Ca10(PO4) 6(OH) 2) is an essential
component of the calcium orthophosphate family. It possesses great dielectric and
biological compatibility properties, diamagnetic properties, thermal stability,
osteoconductivity, and bioactivity, which has a Ca:P molar ratio of 1.67. Since HAp
has a chemical makeup that is very similar to that of natural bone and teeth, it has
the potential to be utilized as a material for the implantation of implants in broken
parts of the human skeletal system. Because of the increasing use of HAp in
medicine, many methods for producing HAp nanoparticles have been discovered.
The preparation conditions of synthesized HAp determine their physical and
chemical characteristics, crystalline structure, and shape. This study gives a
comprehensive information on the properties and production methods of the HAp
in detail and unveile the structure and its properties in detail.
... The Ca/P ratio of the samples obtained at 500 °C and 750 °C was equal to 2.00, which is characteristic of the tetracalcium phosphate phase (TTCP) of the chemical formula Ca 4 O(PO 4 ) 2 8 , was identified in samples calcined at both temperatures. A Ca/P ratio of around 2.00 has been previously observed in studies of synthesis of hydroxyapatite derived from natural agents such as fish scales and mammalian bones [11][12][13][14] . Numerous impurities, such as fluorine, magnesium, sodium, potassium, carbonate and chloride, can be found in bones, as well as small amounts of elements such as strontium, barium, copper, zinc and iron, which are commonly associated with biological apatite and can be seen as substituents in the structure of apatite 12 . ...
In this study, a hydroxyapatite (HA) coating derived from the scales of the Amazonian fish pirarucu (Arapaima gigas) was produced using calcination at 500 and 750 °C and deposited on AISI 316 stainless steel substrate using the process of thermal spraying, high velocity suspension plasma spray (HVSPS). To verify its potential, this material was characterized by X-ray diffraction (XRD), by which characteristic peaks of hydroxyapatite were evidenced. Via X-ray fluorescence (XRF) of the samples, it was observed that the Ca/P ratio was equal to 2.00. Using the Fourier transform infrared (FTIR) spectroscopy and Raman spectroscopy, it was possible to observe the characteristic bands of the HA. For the coating, the mechanical nanoindentation test showed mean Vickers microhardness (VH) values of 93.25 VH for the hydroxyapatite and of 196.57 HV for the substrate. The modulus of elasticity (EIT) was 77.85 GPa for the hydroxyapatite coating and 136.45 GPa for the substrate. Optical microscopy showed that the coating was homogeneously deposited.
... However, the potential for coating cracking during heating and cooling is a serious disadvantage of this coating method, especially in long-term clinical applications, which may cause inflammatory reactions and even osteolysis [135]. To overcome this shortcoming, Boyd et al. [142] used magnetron sputtering (MS) to combine Sr into an HA lattice to form SrHA coating and found that surface morphologies of the coating changed significantly with an increase in SrHA amounts. Christensen et al. [143] found that Sr in the SrHA coating prepared by MS can be effectively released into the surrounding bone tissue. ...
Strontium (Sr) and strontium ranelate (SR) are commonly used therapeutic drugs for patients suffering from osteoporosis. Researches have showed that Sr can significantly improve the biological activity and physicochemical properties of materials in vitro and in vivo. Therefore, a large number of strontium containing biomaterials have been developed for repairing bone defects and promoting osseointegration. In this review, we provide a comprehensive overview of Sr-containing biomaterials along with the current state of their clinical use. For this purpose, the different types of biomaterials including calcium phosphate, bioactive glass, and polymers are discussed and provided future outlook on the fabrication of the next-generation multifunctional and smart biomaterials.
... To produce a stoichiometric HA, the concentrations of compounds required should be adjusted to a Ca/P molar ratio of 1.67 [30]. According to Fig. 1a [4,31,32], as well as elsewhere [4,34]. ...
... HA (Ca 10 (PO 4 ) 6 (OH) 2 ) is one of the noteworthy biomaterials in all other bioactive ceramics due to its osteoconductive and biocompatibility assets. The composition of this ceramic presents a similar composition of human bone minerals and phases [31]. Yan et al. [3] performed biomimetic HA coating on Ti6Al4V lattice surfaces and showed that such surfaces had bioactive characteristics which could be used as bone substitutes. ...
Titanium alloys are widely used for biomedical applications as porous lattice structures whose abilities can be altered via unit cell designs, pore size, and topology. In this study, Ti6Al4V octahedron, star, and dodecahedron cubic and plate lattice structures were designed as 0.20-mm strut diameter with different porosity values (83.06% for octahedron, 53.46% for star, and 63.29% for dodecahedron) and manufactured by laser powder bed fusion. Compression tests were conducted by ISO 13314. The elastic modulus for octahedron, star, and dodecahedron lattices were found 1.7 GPa, 8.6 GPa, and 6.7 GPa, respectively, and results were promising in terms of reducing stress shielding. Relation between relative density and mechanical response was investigated. Chitosan-substituted hydroxyapatite composite coating successfully deposited by electrophoretic deposition on surfaces for biological assessment. Coating increased bioactivity and reduced cell death, especially around implant samples. Chitosan addition ensured an antibacterial effect. Results revealed that mechanical properties and biological responses of structures were affected by the lattice design and pore size.
Graphical abstract
... In order to know the various vibrational bonds responsible for the characteristic properties of SGPDyx phosphors, the FT-IR patterns of phosphors under investigation recorded from 500-1150 cm -1 are presented in Fig. 7. As can see the FT-IR profiles, one can know the presence of (PO 4 ) 3asymmetric stretching vibrations together with Sr-O; O-P-O; P-O and Gd-O vibrations [33][34][35][36][37][38]. The Table 1 summarizes the position and assignment of various FT-IR bands. ...
Sr3Gd(PO4)3 phosphors activated with different concentrations of Dy3+ ions were prepared at 1250 °C/5 h by modified citrate sol-gel combustion technique and examined for lighting applications. The crystalline phase analysis was studied using powder X-ray diffraction and HR-TEM studies. The effect of Dy3+ concentration on morphology was studied through SEM and TEM. Optical band gap energy was estimated using diffused reflectance spectrum. The excitation, emission, luminescence decay and photometric characteristics were studied. The concentration of Dy3+ was optimized for strong and efficient emission through 4F9/2 → 6H15/2, 6H13/2, 6H11/2 transitions. The photometric analysis was done by evaluating the CIE chromaticity coordinates and they were found to be (0.314, 0.360). The generation of white light and transfer of energy among the excited Dy3+ ions were discussed. It was observed that the transfer of energy takes places through dipole-dipole interaction among the excited Dy3+ ions at higher concentrations. The experimental findings show that the 1.0 mol% of Dy3+ -doped Sr3Gd(PO4)3 phosphor has greater potentiality to be used for lighting devices working at 352 nm UV excitation.
Graphical abstract
... The spectra also included a low-intensity peak at 344.5 eV corresponding to carbonate species of alkaline earth metals formed by interaction with atmospheric CO 2 molecules owing to the basic properties of their surface [43]. It should be noted that in the case of Sr-HA and Mg-Sr-HA, the P 2p peak overlapped with the Sr 3d peak [44]; hence, P 2s high-resolution spectra had to be recorded. The P 2s peak was observed at 190.6 eV (Fig. 5, c). ...
Hydroxyapatite (HA) is a biocompatible material widely used in various biomedical applications. Stoichiometric HA has low bioactivity and does not possess antibacterial properties. One way to modify HA properties is to substitute some ions in stoichiometric HA, i.e., to dope HA, for attaining desired properties, e.g., improved bioactivity or an antibacterial effect. This work shows that a soft mechanochemical method of HA synthesis allows to obtain bioactive HA containing strontium ions, magnesium ions, or both. Substituted HAs with substitution degree x(Mg) = 0.5 mol or x(Sr) = 1.5 mol were synthesized, as was cosubstituted HAs contained both magnesium and strontium ions with x(Mg) = 0.5 mol or x(Sr) = 1.5 mol. The resulting materials were investigated by simultaneous thermal analysis, scanning electron microscopy, granulometry, powder X-ray diffraction, Fourier transform infrared, Raman spectroscopy, and X-ray photoelectron spectroscopy. Thermal stability of the obtained materials was studied too. The partial calcium substitution with strontium and/or magnesium changed both HA crystal lattice parameters and positions of absorption bands of phosphate groups in Fourier transform infrared and Raman spectra. X-ray photoelectron spectra of the synthesized materials contain peaks of all elements with binding energies corresponding to substituted HA. The strontium substitution, unlike the magnesium substitution, did not reduce HA thermal stability. The crystal lattice of Sr-substituted HA is stable up to 1300 °C, just as stoichiometric HA. Magnesium cations left HA at 800 °C, forming Mg-substituted β-Ca3(PO4)2. At the cosubstitution, thermal stability of HA became slightly lower. Partial decomposition of the material began already at 700 °C. Accordingly, during manufacturing of medical devices from the proposed materials, their low thermal stability should be taken into account. To preserve the structure of Mg-Sr-cosubstituted HA, heat treatment conditions should not exceed 700 °C.
... The HR-SEM micrograph of SGPTb2.0 phosphor shown in Fig. 1(b) reveals that the particles are appeared to be agglomerated and interconnected together making a continuous structure of irregular shape. The FT-IR spectra of SGPTbx (x = 0 and 1.0 mol%) phosphors in the spectral region from 500 to 1600 cm − 1 shown in Fig. 2 reveals eight IR absorption bands at about 1076, 1016, 999, 949, 685, 592, 548 and 520 cm − 1 corresponding to various functional groups [22][23][24][25][26][27] and their assignment has been summarized in Table 1. ...
The inorganic phosphors doped with different rare earth ions are of more significant to develop new class of lighting devices to fulfill the present technological desires owing to their compact size, high colour rendering index with high luminescence efficiency, eco-friendly behaviour. The present research work reports the synthesis, structural, morphological and optical analysis of Sr3Gd(PO4)3: Tb³⁺ phosphors for lighting applications. These phosphors were synthesized via modified citrate gel-combustion technique with varied concentrations of Tb³⁺ and they were crystallized into BCC phase. The morphological investigations reveal an agglomeration of particles distributed non-uniformly in the crystal lattice. Upon excited at near UV radiation, the phosphors emit intense green luminescence through ⁵D4 → ⁷FJ transitions. The colour perception studies were carried out by evaluating the chromaticity coordinates (x, y). The experimental investigations explore that the studied phosphors are more suitable for lighting applications.
... Cationic and anionic incorporations in the HA lattice are very common in biological apatites, the most diffused being CO 3 2− for OH − (A-type substitution) or for PO 4 3− (B-type substitution), and Cl − and F − for OH − [186]. Besides these ions, Mg, Sr, Zn and Mn substitutions for calcium and silicates for phosphates can be detected in human mineralized tissues [185,187]. A large number of studies have been reported to evaluate the performance of substituted CaP coatings from various points of view [179,183]. ...
Metallic implants sometimes fail in orthopedic surgeries due to insufficient bio-functionality, implant-associated infections, poor osteointegration due to high inertness (Ti, Co–Cr, stainless steel alloys), and a too fast degradation rate (Mg-based alloys). Bioceramic coatings are among the most appropriate solutions for overcoming these drawbacks. After providing a picture of the history as well as the pros and cons of the different types of metallic implants, this review focuses on bioceramic coatings that can be applied on them, including metal oxides, calcium phosphates, silicates, glasses, glass-ceramics, carbon, etc. Various coating strategies and applications are briefly described and discussed, with emphasis on a selected number of highly promising researches. The major trends and future directions in the development of bioceramic coatings are finally suggested.
... Other coating techniques possess limitations with non-uniformity on complex geometries [22,30], poor adherence [31] and cracking [32] which could potentially drive corrosion. Calcium phosphate (CaP) thin films sputtered using hydroxyapatite (HA) targets are among the most investigated sputter coating application for magnesium substrates [33][34][35][36]. Previous studies show that deposition of a CaP coating reduced corrosion rate in magnesium alloy coupons when subject to a degradation study using simulated body fluid (SBF) [21,37]. ...
Magnesium orthopaedic fracture fixation devices can potentially provide significant clinical benefits, such as the elimination of secondary surgeries for device removal due to in-vivo resorption and reduced stress shielding due to reduced device stiffness. However, development, approval, and clinical adoption of magnesium devices has been hindered by the excessively high rates of in-vivo corrosion such that the structural integrity of the device can be catastrophically reduced before fracture healing occurs. Coating of devices with calcium phosphate coatings has been shown to significantly reduce corrosion rates, while enhancing osseointegration. However, the adhesion strength between the CaP coatings and magnesium substrates has not been previously investigated. Clinical insertion of fracture fixation devices such as intramedullary nails and k-wires will impose significant shear loading on the coated surface of the implant. If the effective shear strength of the coating-device interface is not sufficiently high, the coating will be damaged and removed during device insertion. In the current study a bespoke experimental-computational approach is developed to provide a new understanding of the relationship between coating thickness, surface roughness, and effective shear strength of the CaP coating- Mg substrate interface. Nine test cases were created by adjusting either the deposition time (3 thickness values) or the surface treatment of the Mg alloy using SiC paper (3 roughness values) and double-lap shear testing was performed for these coating configurations. Strain development in the Mg substrates was monitored using strain gauges, and failure stress was determined for each configuration. Test results revealed that the effective shear strength of the coating-substrate interface is significantly higher for coatings on the rougher substrate surfaces when compared to those on smoother surfaces. Coating thickness was not found to significantly influence the effective shear strength over the range considered in this study (0.37–1.34 μm). Micro-scale finite element models of lap-shear tests were constructed using experimental profilometry data. Simulations of rough coating-substrate interfaces reveal that significant localised compression occurs at the coating-substrate interface in regions of large asperities. A novel cohesive zone formulation has been developed to simulate compression induced shear hardening, and the resultant simulations are found to accurately predict the significantly higher effective shear strength measured experimentally for rougher coatings compared to smoother Mg substrate surfaces.
... However, they have a tendency to be more evident around abrasion scratches and surface defects. This finding is in good agreement with the morphology found for the sputtered HAP coatings reported by other researchers [44]. It was also reported that the smaller particles lead to a higher bioactivity, more proper for biomedical applications [43]. ...
In this paper, a novel biocompatible alloy defined as FeMoTaTiZr was obtained and functionalized by hydroxyapatite-based coatings (HAP) in order to increase their biocompatibility, bioactivity, and resistance to corrosion for to be used as bone implants. To obtain the surface with antibacterial properties, the HAP coatings were doped with small amount of Zn. The alloy was prepared using the VAR (Vacuum Arc Remelting) equipment, while the coatings by RF magnetron sputtering method. The EDS analysis confirmed the presence of Ca and P in the case of all developed coatings, having Ca/P ratio ranged from 1.69 (undoped HAP) to 1.96 (Zn doped HAP). The (Ca+Zn)/P ration was of about 2.15 for the Zn doped HAP coatings. The XRD and ATR-FTIR investigations confirmed the presence of calcium phosphate phases. After coating with HAP, the roughness of uncoated substrates increased with 1.4 times, and it was considerably increased by the Zn addition with 2.4 times. The electrochemical tests showed that the un-doped HAP exhibited good corrosion behavior, while Zn doped HAP coatings have a high dissolution rate in fetal bovine serum, being more proper as a biodegradable material.
... Bigi et al. (2007) showed Sr 2+ ions preferentially incorporate at M(1) sites of apatite crystals in hydrothermal condition. M(1) sites are larger than M(2) and also have longer M(1)-O bond distances, thereupon less stress and distortion will apply in hydrothermal condition (Boyd et al. 2015). ...
Titanium and its alloys are considered as appropriate replacements for the irreparable bone. Calcium phosphate coatings are widely used to improve the osteoinduction and osseointegration ability of titanium alloys. To further improve the performance of the calcium phosphate-coated implants, strontium (Sr) was introduced to partially replace the calcium ions. In this study, the effect of Sr ion addition on the fluorohydroxyapatite (FHA)-coated Ti6Al4V alloy was investigated and all the coatings were treated under hydrothermal condition. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to investigate the phases and microstructures, respectively. Shear tests were done to evaluate the bond strength of the coating layer. MTT, adhesion, and alkaline phosphatase tests were performed to evaluate the biocompatibility and osteogenic behavior of the samples. Results showed that the average crystallite size for the strontium-doped FHA samples was 48 nm and the bond strength had increased 13.15% in comparison with FHA-coated samples. Analysis of variance showed p value for all MTT tests at more than 0.322 and there was not any evidence of cell death after 7 days. The results of the ALP test showed that the increase of the cell activity in Sr samples from day 7 to 14 is three times higher than the FHA ones.
... The naturally formed bio-apatite has trace amounts of fluoride, magnesium, sodium, potassium, carbonate, chloride, zinc, barium, iron, strontium, copper, etc [3,4]. Studies showed that the incorporation of different foreign cations and anions into synthetic HA structures enhanced its osteoblastic response [5]. HA in general, is brittle and is not suitable for load-bearing applications. ...
The bioactive and biocompatible properties of hydroxyapatite (HA) promote the osseointegration process. To enhance other bio-functions of HA such as improving the antibacterial property of the implant, increasing the rate of cell proliferation, or improving tissue generation capability, HA is substituted with many elements such as Zn, Cl, Ba, Fe, Cu, Ag, Sr, F, Na, etc. This study reports development of Magnesium substituted HA (Mg-HA) coatings on Ti6Al4V substrates using the dip coating technique. To improve the adhesion and stability of the coating, an intermediate layer of shellac was applied between the coating and Ti6Al4V substrate. The dip coating process parameters were optimized using the Taguchi technique and it was found that dipping time of 35 s and 13% w/w of shellac concentration provided the maximum bonding strength of 12.5 MPa. The biocompatibility, dissolution, and corrosion study of the developed coating using the optimal parameters obtained were carried out in this study. An improvement in cell growth and cell proliferation was observed in the extract medium prepared from coated substrates. Release of Ca, P and Mg ions from the surface of the coated substrate into the simulated body fluid (SBF) was found to be almost constant which shows the stability of the thin film coating formed. The Mg-HA coated substrate also exhibited better corrosion resistance than the uncoated substrate.
... The peak at 631 cm -1 in HA was due to the librational mode, ν L , of the hydroxyl group. This peak was absent in Se-HA and Se-Sr-HA as reported by Boyd et al. due to the replacement of carbonate at OH sites [359]. ...
For treatment of severe bone fractures and damage, synthetic bone grafts have extensively been used as substituting natural bone tissue. Hydroxyapatite (HA) is being extensively used for numerous biomedical applications, specially in orthopaedics and bone replacement applications because of its resemblance to the inorganic part of natural bone. This work aimed to develop novel substituted hydroxyapatite materials having antibacterial properties, as a potential approach to address infection problems in orthopaedic surgeries. This thesis presents a variety of novel single and co-substituted HA powders synthesized by wet precipitation and solid-state methods; afterwards, characterisation of the new materials was carried out using several techniques to determine the crystallographic structure, physiochemical properties, elemental composition, antibacterial and cellular properties of novel substituted HA powders. The new compositions are characterized by substitution of different metal ions in HA, namely: selenite/selenate (SeO3 2- or SeO4 2-), cerium (Ce3+ or Ce4+), copper (Cu+ or Cu2+), and strontium (Sr2+) in various concentrations to improve antibacterial activity, and so to prevent the demand for the usage of antibiotics. Crystallographic studies by X-ray diffraction (XRD) and Rietveld refinement were performed to explain the effect of ion substitution on the HA lattice structure. The compositional and morphological analysis was carried out by using X-ray powder fluorescence (XRF) and Scanning Electron Microscopy (SEM), respectively. Complete chemical recognition was carried out with Fourier transform infrared (FTIR) and Raman spectroscopy to reveal the functional groups present in substituted HA. Biological studies of substituted HA using both direct and in-direct cell culture routes revealed positive cell response with MG-63 and MC3T3-E1 cell lines. Disc diffusion method and turbidity measurements were used to evaluate antibacterial properties of samples against Gram-positive bacteria Staphylococcus carnosus (S. carnosus) and Gram-negative bacteria Escherichia coli (E. coli). The crystallographic results confirmed the substitution of metal ions in the HA crystal structure, as the change in lattice parameters, crystallinity and crystallite size was evidenced, which shows the impact of ion substitution in the HA lattice structure. The substituted ions showed a small deviation of the achieved concentration from the predictable reaction stoichiometry. Moreover, surface charge (evaluated by zeta potential measurements) was revealed to be contingent on the type of substitution. The HA powders immersed in simulated body fluid (SBF) exhibited moderate release of ions which were measured using Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES). The levels of released ions were directly proportional to the concentration of substituted ions in HA. The type and concentration of substituted ions had a significant influence on cellular activity. HA substituted with SeO3 2-/SeO4 2-, Ce3+/Ce4+, and Cu+/Cu2+ ions exhibited different levels of antibacterial properties against both bacterial strains, which was ascribed to the type and concentration of substituted ions and also to the ion release profiles. The successfully substituted HA materials showing best results in term of significant antibacterial and biological properties were selected for coatings on metallic implants. Electrophoretic deposition (EPD) techniques (AC and DC) were used to fabricate bioactive and antibacterial composite coatings based on chitosan and substituted HA (pure HA, selenium substituted HA (Se-HA), strontium substituted HA (Sr-HA), and selenium-strontium co-substituted HA (Se-Sr-HA)), as a prospective approach to tackle intrinsic limitation of metallic implants, for example lack of bioactivity and antibacterial effects. In this approach, the substituted HA particles acted as carriers of metal ions for antibacterial activity while chitosan acted as matrix to improve the mechanical properties and to promote osseointegration of the metallic implants. The processing parameters of EPD techniques (AC and DC) were optimized to obtain the desired properties of coatings. The composite coatings exhibited significant adhesion strength, wetting behaviour, and in vitro bioactivity. The release of SeO3 2-/SeO4 2- ions confers antibacterial activity against both S. carnosus and E. coli bacterial strains. Moreover, the chitosan/Se-Sr-HA based composite coatings revealed significant cell viability of 75 % (determined by the WST-8 assay). Furthermore, the co-substitution of Sr2+ was shown to improve cell viability of the coatings. Likewise, the adhesion of MC3T3-E1 cells on the coating surface was significant revealing strong cell-matrix adhesion and cell spreading morphology. To summarize, EPD was confirmed as an appropriate coating method for fabricating substituted HA-based composite coatings for orthopaedic implants. To the best of the authors’ knowledge Se-Sr-HA using wet precipitation method, and cerium substituted HA (Ce-HA) using solid-state route were synthesized and characterized for the first time in this thesis. Moreover, chitosan/Se-Sr-HA composite coatings as bioactive and antibacterial coatings were developed and tested for the first time, with successful results which indicate that such novel coatings could be potentially used in orthopaedic implants applications.
Six commonly used synthesis techniques for calcium phosphates are solid-state, mechano-chemical, wet-chemical precipitation, hydrolysis, sol–gel, and hydrothermal methods.
The increasing demand for orthopedic implants has driven the search for materials that combine strength, biocompatibility, and long lifetime. Compared to stainless steel and Co-Cr-based alloys, titanium (Ti) and its alloys are favored for biomedical implants because of their high strength, corrosion resistance, and biocompatibility. This comprehensive review delivers a wide overview of the field of titanium-based biomaterials for orthopedic implants applications, focusing on their types, mechanical and chemical resistance, surface modifications, innovations in fabrication techniques, titanium matrix composites, and machine learning advancements. Titanium alloys of different crystalline phases, including α, near-α, (α + β), β, and shape memory alloys, offer diverse options for orthopedic applications. Strengthening properties, wear, fatigue, and corrosion resistance are crucial factors influencing the performance and reliability of titanium implants. Moreover, this review discussed the challenges to titanium-based biomaterial durability through surface modifications to enhance their biofunction, wear resistance, corrosion resistance, and antibacterial properties. Recent developments in fabrication techniques for titanium-based biomaterials are also discussed. Eventually, this review investigated how machine learning (ML) revolutionized titanium orthopedic implants by providing insights into the behavior of new alloys, aiding in manufacturing optimization, allowing for real-time quality control, and advancing the development of personalized, biocompatible, and reliable implants.
Titanium (Ti) has been widely used in biomedical implants due to its excellent mechanical properties and biocompatibility. However, the “stress shielding” effect greatly limits the application of titanium alloys in medical devices. Studies have shown that the incorporation of bioactive elements into the titanium alloy matrix is an effective way to impart specific biological functions to the material through the sustained release of biofunctional elements. Magnesium (Mg) and its alloys have good bioactivity and are potential candidates for biodegradable metal implants. Ti‐Mg composites are of increasing interest for biomedical applications. However, the incompatibility between Ti and Mg, such as immiscibility and large melting point difference, has been an insurmountable obstacle to the successful preparation of Ti‐Mg composites by casting or powder sintering processes. How to successfully prepare well‐sintered Ti‐Mg composites by powder metallurgical methods has been a challenge. In addition, the biocompatibility of Ti‐Mg metal matrix composites in vivo still needs to be further investigated. In this paper, we review the recent research progress of Ti‐Mg composites for biomedical implants, focusing on their preparation methods, properties. From microstructure to properties, the composites are systematically reviewed and discussed. The preparation methods such as powder metallurgy technology and 3D printing are introduced in detail, and their advantages and disadvantages are compared and analyzed. In addition, the mechanical and corrosion resistance as well as biocompatibility of Ti‐Mg composites are discussed. Based on this, the problems and development prospects of Ti‐Mg metal matrix composites are presented.
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By using a low-temperature plasma glow discharge with argon gas and C2H2 as a carbon source, niobium carbide thin films were applied on a commercially pure titanium substrate. The coatings were deposited in three different deposition times: Group-1 with 2-h deposition time, group-2 with 4-h deposition time and group-3 with 6-h deposition time. The films were analysed for phase composition, microstructure, surface morphology, roughness and wettability as a function of deposition time. The X-ray diffraction (XRD) patterns suggest the formation of various phases (either orthorhombic-Nb2C or cubic-NbC). It is worth noting that deposition time affects the crystal structure of both phases, with Nb2C having a more noticeable effect due to a noticeable shift in the related XRD pattern. This might be attributable to changes in carbon content and sputtered niobium ions throughout the deposition process when the chamber gas conditions were verified to form phase pure NbC. The scanning electron microscopy images of the deposited NbC films display a microstructure that shows good regularity and homogeneity; a uniform morphology is revealed with an agglomerating characteristic of the material. Increased deposition time results in less surface roughness, according to atomic force microscope analysis. In contrast, the measurements of the water contact angle revealed only a little improvement in wettability as the deposition period increased.
Ti alloys have many excellent properties, including low elastic modulus, desired corrosion resistance, nontoxicity, and biocompatibility. Hence, they promise to be major hard-tissue implant biomaterials (HTIBs). However, some properties, like surface hardness, wearability, and cellular activity, need to be enhanced. Moreover, their corrosion resistance in simulated body fluids and biocompatibility also need to be investigated systematically before practical applications. As HTIBs, the primary properties in clinical applications are wearability, corrosion resistance, and biocompatibility. Surface modification is a commonly used effective way to improve the above-mentioned disadvantages. This work is a brief review of the main surface modification technologies of Ti alloys for HTIBs (hereafter referred to as Ti alloys). The main surface modification technologies of Ti alloys are divided into four types, namely, physical technologies, chemical technologies, electrochemical technologies, and surface plastic deformation technologies. The principle and applications of these four types of surface modification technologies on Ti alloys are introduced one by one. Finally, the future directions for the surface modification of Ti alloys are proposed.
Currently, there is a growing market for implant coatings that efficiently ward off bacterial infections while aiding in clinical osseointegration. Due to its potential to have a number of functions (including osteogenic activity and antibacterial activity) for bone implantation, the hydroxyapatite (HA) coating doped with multiple ions has drawn a lot of attention. In this study, innovative nanohydroxyapatite coatings containing simultaneous Sr2+, Mn2+, and Ag+ substitutions (MnSrAgHA) were devised and effectively electrodedeposited on pure titanium. That is, the antibacterial ability of MnSrAgHA was enhanced by Ag+, Sr2+ and Mn2+ not only can balance the potential cytotoxicity of Ag+, but also can improve the bone repair rate of composite materials. Some experimental (FE‐SEM, XPS and EDS, etc.) results about the characterization show that Sr2+, Mn2+ and Ag+ can uniformly combine into the HA lattice to form the SrMnAgHA coating. The MnSrAgHA coating surface was rather dense, with numerous needle‐like or flower cluster crystals, and the coating thickness is approximately 10 μm. Moreover, compared with other coatings (HA, AgHA and SrAgHA), the MnSrAgHA coating had a smaller roughness and higher contact angle. However, the contact angle of MnSrAgHA was still within the hydrophilic range. Staphylococcus aureus growth was inhibited by the MnSrAgHA coating, and the antibacterial rate was almost 100 %. The MnSrAgHA coating dramatically enhanced cell proliferation, adhesion, and differentiation abilities, according to in‐vitro cell culture studies. As expected, osteoblasts are not significantly cytotoxic by the MnSrAgHA coating. Due to its adaptability, the multi‐element co‐doped HA coating (MnSrAgHA) offers enormous clinical application potential in anti‐infective repair. The fabrication process of the MnSrAgHA composite coating on Ti is shown in Graphical Abstract (for review). A novel nano‐HA coating simultaneously substituted by Mn2+, Sr2+ and Ag+ was successfully synthesized on titanium substrates by electrochemical deposition technique.The following series of experiments were verified: 1) the surface microstructure, phase composition, roughness, hydrophilicity of the coated implants; 2) the release behavior of Sr2+, Ag+ and Mn2+ from the MnSrAgHA coating; 3) the in vitro cellular responses of the composite coatings; 4) Effect of Ag+ on antibacterial properties of composite coatings.
The stress shielding effect caused by traditional metal implants is circumvented by using polyetheretherketone (PEEK), whose elastic modulus similar to that of natural bone; however, the biologically inert nature of PEEK limits its application. Endowing PEEK with biological activity to promote osseointegration would increase its applicability for bone replacement implants. We performed a biomimetic study inspired by mineralized collagen fiber bundles that contact bone marrow mesenchymal stem cells (BMMSCs) on the native trabecular bone surface. The PEEK surface (P) was first sulfonated with sulfuric acid to form a porous network structure (sP). The surface was then encapsulated with amorphous hydroxyapatite (HA) by magnetron sputtering to form a biomimetic scaffold that resembles mineralized collagen fiber bundles (sPHA). Amorphous HA simulates the composition of osteogenic regions in vivo and exhibits strong biological activity. Based on in vitro cytological experiments, more favorable cell adhesion and osteogenic differentiation could be attained with the novel active surface of sPHA than with SP. The results of in vivo experiments showed that the novel surface exhibited osteoinductive and osteoconductive activity and facilitated bone formation and osseointegration. Therefore, the surface modification strategy can significantly improve the biological activity of PEEK, facilitate effective osseointegration and inspiring further bionic modification of other inert polymers similar to PEEK. This article is protected by copyright. All rights reserved
Crayfish shell is an abundant natural waste and is also a potential biosorbent for pollutants, especially, heavy metals. In this study, the safety of the use of crayfish shell as a biosorbent was first assessed by release experiments involving primary heavy metal ions, such as Cu ²⁺ , Zn ²⁺ , and Cr ³⁺ , in aqueous solution under different environmental conditions. The release concentrations of heavy metals were dependent on pH, ionic strength, and humic acid; and the maximum release concentrations of heavy metals were still lower than the national standard. Specifically, Cu ²⁺ and Pb ²⁺ removal by crayfish shell in synthetic wastewater was investigated. The removal process involved biosorption, precipitation, and complexation, and the results indicate that crayfish shell is an excellent biosorbent for Cu ²⁺ and Pb ²⁺ removal. The precipitation step is particularly dependent on Ca species, pH, and temperature. The maximum removal capacities of Pb ²⁺ and Cu ²⁺ were 676.20 and 119.98 mg/g, respectively. The related precipitates and the generated complex products include Cu 2 CO 3 (OH) 2 , Ca 2 CuO 3 , CuCO 3 , Pb 2 CO 3 (OH) 2 , CaPb 3 O 4 , and PbCO 3 .
Thin film is a modern technology aimed at improving the structural, electrical, magnetic, optical, and mechanical properties of bulk materials. This technology has so far found applications in integrated circuits, semiconductor devices, transistors, light-emitting diodes, light crystal displays and photoconductors, rectifiers, solar cells, sensors, and micro-electromechanical systems (MEMS). Methods of thin film deposition such as physical and chemical vapor deposition (PVD and CVD), sputtering, spin and dip coating, and spray pyrolysis have been utilized for several years. But in recent times, the atomic layer deposition (ALD) technique has attracted the attention of researchers. In this current review, we have explored the most used techniques in the depositions of thin film materials with a focus on the properties of film produced, and the advantages and disadvantages of each technique. Generally, it was observed that the quality of films produced by these techniques depends greatly on the choice of substrate, deposition temperature, temperature window, and precursor used. It concluded by identifying ALD as an optimum technique in depositing ultra-thin film materials due to its simplicity, reproducibility, control over film composition and thickness, and high conformal deposited films at the atomic level. This study has established the opportunity for upcoming researchers to have an insight of selecting the most suitable technique for their study in various fields of research. Finally, the challenges and future perspectives of deposition techniques were highlighted.
Synthetic biomaterials are used to overcome the limited quantity of human-derived biomaterials and to impart additional biofunctionality. Although numerous synthetic processes have been developed using various phases and methods, currently commonly used processes have some issues, such as a long process time and difficulties with extensive size control and high-concentration metal ion substitution to achieve additional functionality. Herein, we introduce a rapid synthesis method using a laser-induced hydrothermal process. Based on the thermal interaction between the laser pulses and titanium, which was used as a thermal reservoir, hydroxyapatite particles ranging from nanometer to micrometer scale could be synthesized in seconds. Further, this method enabled selective metal ion substitution into the apatite matrix with a controllable concentration. We calculated the maximum temperature achieved by laser irradiation at the surface of the thermal reservoir based on the validation of three simplification assumptions. Subsequent linear regression analysis showed that laser-induced hydrothermal synthesis follows an Arrhenius chemical reaction. Hydroxyapatite and Mg2+-, Sr2+-, and Zn2+-substituted apatite powders promoted bone cell attachment and proliferation ability due to ion release from the hydroxyapatite and the selective ion-substituted apatite powders, which had a low crystallinity and relatively high solubility. Laser-induced hydrothermal synthesis is expected to become a powerful ceramic material synthesis technology.
High (cation/Ca+cation=16 mol.%) and low (cation/ca+cation=4.76 mol.%) concentrations of Mg 2+ , Zn 2+ and Sr 2+ , as divalent cations with interesting biological properties were tried to incorporate into the structure of well-known bioceramic: hydroxyapatite (HA). An established hydrothermal synthesis method was employed for preparation of HA in whisker-like morphology. Consequently, the possibility of synthesizing HA whiskers (HAWs) with cationic substitutions and effects of the introduced ions on morphology, structure and composition of HA products were evaluated. Almost, all the cation-substituted preparations could maintain the apatite phase, while the decrease in crystallite size and crystallinity was obvious. Lattice parameters (a, c) of the hexagonal system of HA were also affected in accordance with the type and amount of substituting cation. Zn 2+ and high amounts of Mg 2+ dramatically inhibited formation of whisker-like apatite and promoted formation of a mixture of hexagonal prism-like and flaky bundles, or hexagonal and multifaceted morphologies, respectively. However, Sr 2+ exhibited minimum inhibitory effect on HAWs formation. Therefore, Sr-and Mg-substituted (low concentration of Mg) HAWs could be prepared for their potential biomedical applications.
High (cation/Ca+cation=16 mol.%) and low (cation/ca+cation=4.76 mol.%) concentrations of Mg 2+ , Zn 2+ and Sr 2+ , as divalent cations with interesting biological properties were tried to incorporate into the structure of well-known bioceramic: hydroxyapatite (HA). An established hydrothermal synthesis method was employed for preparation of HA in whisker-like morphology. Consequently, the possibility of synthesizing HA whiskers (HAWs) with cationic substitutions and effects of the introduced ions on morphology, structure and composition of HA products were evaluated. Almost, all the cation-substituted preparations could maintain the apatite phase, while the decrease in crystallite size and crystallinity was obvious. Lattice parameters (a, c) of the hexagonal system of HA were also affected in accordance with the type and amount of substituting cation. Zn 2+ and high amounts of Mg 2+ dramatically inhibited formation of whisker-like apatite and promoted formation of a mixture of hexagonal prism-like and flaky bundles, or hexagonal and multifaceted morphologies, respectively. However, Sr 2+ exhibited minimum inhibitory effect on HAWs formation. Therefore, Sr-and Mg-substituted (low concentration of Mg) HAWs could be prepared for their potential biomedical applications.
A series of Pr3+ activated Sr3Gd(1‐x)(PO4)3:xPr3+ (0 ≤ x ≤ 2.0 mol%) phosphors were prepared and their structural, compositional and luminescence properties were investigated. The X‐ray diffraction profiles indicate that the studied phosphors crystallized into body centered cubic structure and the Pr3+ ions have no influence on Sr3Gd(PO4)3 phase. The high‐resolution scanning electron microscopic micrograph shows the agglomeration of particles that were inter‐connected and forms irregular shape Sr3Gd(PO4)3 structure. The excitation transitions corresponding to Pr3+: 3H4 → 3P2,1,0 transitions at 445, 471 and 483 nm, respectively matched well with the emission of blue‐LED chip. The emission spectra show strong reddish‐orange luminescence through 1D2 → 3H4 transition when excited at 445 nm blue wavelength. The synthesized phosphors were potential to develop reddish‐orange lighting devices.
The SGPEux phosphors of composition Sr3Gd(1–x)(PO4)3:xEu³⁺ were synthesized by modified citrate-gel combustion method for white LED sources. The optimum conditions of synthesis were obtained from thermogravimetric and differential scanning calorimetry. The synthesized phosphors were crystallized into BCC structure with JCPDS No. 29-1301. The presence of various bonds due to stretching and bending vibrations of different functional groups were studied through Fourier transform infrared spectroscopy. The morphology was examined using high-resolution scanning electron microscopy. The luminescence analysis was carried out through photoluminescence excitation and emission studies. The charge transfer band and f-f transitions of Gd³⁺ and Eu³⁺ ions cause a transfer of energy from Gd³⁺ to Eu³⁺. A suitable excitation wavelength for efficient luminescence was selected as 273 nm by studying the emission properties at different excitations. The quenching in luminescence noticed beyond 2.0 mol% was assigned to non-radiative transitions at higher Eu³⁺ concentrations. The analysis of colour perception and colour temperature of emitted luminescence was studied using chromaticity coordinates evaluated from the emission spectra. The observed results suggest that the 2.0 mol% of Eu³⁺ doped SGPEu phosphor has more proficiency to design new class of w-LED sources.
The photoluminescence properties of different concentrations of Sm³⁺ activated Sr3Gd(PO4)3 phosphors synthesized by modified citrate gel-combustion method were investigated for white light emitting diode (w-LED) applications. The studied phosphors were characterized through powder x-ray diffraction (PXRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), photoluminescence excitation, emission and lifetime studies. The PXRD profiles confirmed the body centered cubic structure of undoped and Sm³⁺ -doped phosphors. The SEM studies showed the distribution and agglomeration of particles. The characteristic emission transitions such as ⁴G5/2 → ⁶H5/2 (∼561 nm), ⁴G5/2 → ⁶H7/2 (∼598 nm), ⁴G5/2 → ⁶H9/2 (∼645 nm) and ⁴G5/2 → ⁶H11/2 (∼705 nm) were noticed at their respective positions when excited at 403 nm wavelength. The highest luminescence intensity was found for 1.0 mol% of Sm³⁺ doped phosphors at 403 nm excitation showing luminescence quenching and it was ascribed to dipole-dipole interaction type of energy transfer among the excited Sm³⁺ ions at higher concentrations. The reddish-orange colour of emitted luminescence was examined by evaluating the chromaticity coordinates. The experimental results confirm the potentiality of studied phosphors for w-LED applications.
Zinc and its alloys show a good application prospect as a new biodegradable material. However, one of the drawbacks is that Zn and its alloys would induce the release of more Zn ions, which are reported to be cytotoxic to cells. In this study, a Ca-P-Sr bioactive coating was prepared on the surface of pure zinc by the hydrothermal method to address this issue. The morphology, thickness, and composition were characterized, and the effects of the coating on the degradation, cell viability, and ALP staining were investigated. The results demonstrated that the degradation rate of pure zinc was reduced, while the cytocompatibility was significantly improved after pure zinc was treated with Ca-P-Sr coating. It is considered that the Ca-P-Sr bioactive coating prepared by the hydrothermal method has promising application in the clinic.
The world of biomaterials has been continuously evolving. Where in the past
only mono-material implants were used, the growth in technology and col-
laboration between researchers from different sectors has led to a tremendous
improvement in implant industry. Nowadays, composite materials are one of
the leading research areas for biomedical applications. When we look toward
hard tissue applications, metal-based composites seem to be desirable candi-
dates. Metals provide the mechanical and physical properties needed for load-
bearing applications, which when merged with beneficial properties of bioce-
ramics/polymers can help in the creation of remarkable bioactive as well
biodegradable implants. Keeping this in mind, this review will focus on vari-
ous production routes of metal-based composite materials for hard tissue
applications. Where possible, the pros and cons of the techniques have been
provided.
This chapter provides a review of the main types of bioactive ceramics and glasses used or under development for tissue engineering applications. Bioactive ceramics and glasses have been researched and developed mainly for the repair and regeneration of bone. However, increasing studies have shown the capacity of bioactive glasses to heal soft tissue wounds. The most widely used bioactive ceramics are the calcium phosphate bioceramics such as hydroxyapatite, beta-tricalcium phosphate, and biphasic calcium phosphate. Increasing research interest has been observed regarding the incorporation of therapeutic ions within the composition of calcium phosphate ceramics to enhance their functionality. While silicate-based bioactive glasses, such as the compositions designated 45S5 and 13–93, have received considerable attention, other compositions, such as borate and phosphate bioactive glasses, are also being studied and applied. In addition to providing a three-dimensional scaffold to guide tissue regeneration, bioactive ceramics and glasses are also being developed as delivery systems for cells, growth factors, synthetic drugs, natural herbal compounds and ions to enhance tissue regeneration. Conventional bioactive composites, composed of a discrete bioactive ceramic or glass phase dispersed in a biodegradable matrix, and inorganic–organic hybrids, composed of an inorganic bioactive component and a biodegradable organic component that interact at the nanoscale, will also be described. Properties of these bioactive ceramics and glasses, as well as their performance in vitro and in vivo are reviewed.
High (cation/Ca+cation=16 mol.%) and low (cation/ca+cation=4.76 mol.%) concentrations of Mg 2+ , Zn 2+ and Sr 2+ , as divalent cations with interesting biological properties were tried to incorporate into the structure of well-known bioceramic: hydroxyapatite (HA). An established hydrothermal synthesis method was employed for preparation of HA in whisker-like morphology. Consequently, the possibility of synthesizing HA whiskers (HAWs) with cationic substitutions and effects of the introduced ions on morphology, structure and composition of HA products were evaluated. Almost, all the cation-substituted preparations could maintain the apatite phase, while the decrease in crystallite size and crystallinity was obvious. Lattice parameters (a, c) of the hexagonal system of HA were also affected in accordance with the type and amount of substituting cation. Zn 2+ and high amounts of Mg 2+ dramatically inhibited formation of whisker-like apatite and promoted formation of a mixture of hexagonal prism-like and flaky bundles, or hexagonal and multifaceted morphologies, respectively. However, Sr 2+ exhibited minimum inhibitory effect on HAWs formation. Therefore, Sr-and Mg-substituted (low concentration of Mg) HAWs could be prepared for their potential biomedical applications.
Zinc-based biometal is expected to become a new generation of biodegradable implants. Due to its antibacterial and biocompatibility in vivo, zinc metals is recently considered to be the most promising biodegradable metal, However, cytotoxicity is the thorny problem that currently restrict its application, due to the excessive Zn ions released during degradation. In order to solve these problems, dopamine modified strontium-doped hydroxyapatite coating (SrHA/PDA) was fabricated on alkali-treated pure zinc to improve its corrosion rate and cytocompatibility by electrodeposition for the first time. The obtained coating showed a dense structure and high crystallinity, which was attributed to the attraction of Ca²⁺ ions by polydopamine. The results showed that the SrHA/PDA coating delayedthe degradation rate of zinc metal, which reduced the release of Zn²⁺, thereby reducing its cytotoxicity. Additionally, electrochemical tests showed that SrHA/PDA coating can reduce the corrosion rate of pure zinc. In vitro cell viability showed that even at high Zn²⁺ concentrations (3.11 mg/L), preosteoblasts (MC3T3-E1) cells proliferated at a high rate on SrHA/PDA, thus confirming that Sr²⁺ counteracted the cytotoxic effects of Zn²⁺ and promoted cell differentiation. Moreover, the SrHA/PDA coating still maintained excellent antibacterial effects against pathogenic bacterial strains (Escherichia coli and Staphylococcus aureus). Mild pH changes had no significant effect on the viability of cells and bacterias. Collectively, the present study elucidated that by coating SrHA/PDA/Zn(OH)2 on Zn, a controllable corrosion rate, original antibacterial properties and better cell compatibility can be achieved. This provided a new strategy for the surface modification of biodegradable Zn.
Hydroxyapatite (HAP) has been considered to be one of the most preferred scaffold materials among many in the last decade for the bone tissue engineering. Be it prosthetic implants, scaffolds or artificial bone cement, hydroxyapatite has received highest attraction among all due to its chemical and physical properties similar to that of human bone. Although it can be used in the bone tissue engineering as the original composition; for enhancing its different properties relevant to in vivo applications, the calcium in HAP may also be replaced by other atomic dopants depending on usage. Here, we review various HAP coating agents and methods, their merits and demerits. We also review various HAP doping materials, including both cationic as well as anionic materials. We discuss the effects and usage of substitution of hydroxyapatite and their subsequent usage in both bone tissue engineering and maxillofacial surgeries. We consider various research articles published in recent times to accomplish detailed discussion on the subject.
Calcium phosphate coatings are widely used to increase the biocompatibility of metal implants. Nowadays various dopants in the structure of calcium phosphate coatings are actively studied. Nitric oxygen is known as an essential mediator of blood flow. Its presence in the structure of calcium phosphate coating can stimulate angiogenesis and promote osseointegration of the implant. This article is dedicated to the study of morphology and physico-chemical properties of the calcium phosphate coatings formed via reactive RF-$$$magnetron sputtering of hydroxyapatite in the mixture of noble gases (Ne, Ar and Xe) and nitrogen with the same volume concentrations. There is a decrease in grain size and an increase in roughness with the growth of the atomic mass of noble gas in the mixture with nitrogen. The Ca/P ratio also decreases with the increase in the atomic mass of noble gas. Coatings formed in Ne + N 2 and Xe + N 2 gas mixtures are characterized by higher surface free energy in comparison with the ones formed in Ar + N 2 . It allows us to suggest that the coatings formed in Ne + N 2 and Xe + N 2 are more biocompatible than ones formed in Ar + N 2 , however, additional studies are needed to prove it.
Owing to its inductive attributes, hydroxyapatite is an ideal reinforcement to tailor the degradation kinetics of magnesium-based temporary orthopedic implants. However, the large difference in the melting temperature of hydroxyapatite and magnesium lead to an insignificant interaction between them during the sintering process, which has been a major limitation in their consolidation. Doping of pure HA with Mg2+ and Zn2+ ions could be a viable solution by making it coherent with the Mg matrix. Further, such doping also results in a chemistry more similar to the natural apatite in human bone. In this study, Mg2+ and Zn2+ ions doped hydroxyapatite (CoHA) is synthesized and reinforced to obtain high density in Mg-based composites, fabricated through spark plasma sintering. Composite with 15 wt % CoHA offered ∼113% improvement in the ultimate compressive strength. Higher relative density, due to improved consolidation, might be the reason for higher mechanical strength. Hydrogen evolution (up to 64 h) and static immersion studies (up to 28 days) revealed comparatively higher corrosion resistance for 10 wt% CoHA composites. This study gives insight into the potential of fabrication and designing of the M3Z-CoHA composites for temporary orthopedic implants.
New materials that mimic natural bone properties, matching functional, mechanical, and biological properties have been continuously developed to rehabilitate bone defects. Desirably, ‘tissue engineering’ has been a multidisciplinary ground that uses the principles of life sciences and engineering for the biological replacements that restore or replace the tissue function or a whole organ. Nevertheless, the bone grafting treatment has numerous restrictions, counting the major hazards of morbidity from the sites where donor bone grafts are removed, the likelihood for an immune rejection or bacterial transport from the donor site (in case of allogeneic grafting), and the inadequate availability of donor bone grafts that can meet the current demands. Since the proper growth of synthetic materials for implantable bones encourages the reconstruction of bone tissues by providing strong structural support without any damages to the interferences of biological tissue. To serve for such behavior, the biodegradable matrices provide temporary scaffolds within which the bone tissues can regenerate. Typically, the thermoplastic aliphatic polyesters are found to serve this purpose. The great significance of this field lies in the in vitro growth of precise cells on porous matrices (scaffolds) to generate three-dimensional (3D) tissues that can be entrenched into the location of tissue/bone damage. Numerous gifts have been gifted by our nature to advance and preserve the well-being of all living things either directly or indirectly. This review focuses on the recent advances in polymer-based hydroxyapatite scaffolds including their properties and applications.
Magnesium and its alloys have been introduced as innovative orthopedic implants due to their potential in serving lightweight, bio-active, degradable, and biocompatible properties. Mg and its alloys corrode rapidly in a biological environment and result in losing mechanical properties. However, to enhance corrosion resistance and mechanical properties, Mg alloy was plasma-sprayed with pure hydroxyapatite (HA) and HA-reinforced with strontium (Sr) powder at three levels (4, 8, and 12 wt.%). Surface parameters such as microhardness, surface roughness, and wettability were examined. The electrochemical technique was used to study the corrosion behavior in Ringer’s solution. The outcomes confirmed that with the rise in Sr content in pure HA coatings, the surface properties as well as the corrosion resistance improved significantly. The contact angle of substrates under examination exhibits hydrophilic nature. Collectively, the findings of this study signify HA/Sr reinforced coatings are a promising approach to improve surface properties and corrosion behavior of Mg alloys for future bone implant applications.
A series of SrMg2(PO4)2: Eu²⁺‐Eu³⁺, Dy³⁺ phosphors were successfully synthesized by a high temperature solid state method in air atmosphere. The structures using X‐ray diffraction (XRD) and luminescent properties of the samples were studied in detailed. SrMg2(PO4)2: Eu2 +‐Eu³⁺ samples can emit adjustable blue‐violet light by controlling the proportion of dopant concentration of europium and dysprosium under 340 nm excitation. While Dy³⁺ exhibits typical blue and yellow emission under 350 nm excitation. The energy transferred from Eu³⁺ to Dy³⁺ in Dy and Eu co‐doped system is discovered by comparing the fluorescence spectra of single‐doped system. In addition, the color coordinates of the International Commission on lighting (CIE) to indicate that SrMg2(PO4)2: Eu²⁺‐Eu³⁺, Dy³⁺ can be considered as a potential blue‐purple phosphor for white light‐emitting diodes (LEDs) applications.
Surgical implants are generally made-up of light metal or alloys like titanium and titanium alloys. In this study, attempts are made to enhance the mechanical properties and corrosion resistance by developing a protective layer with plasma-sprayed strontium-reinforced hydroxyapatite (HA-Sr) coatings at three levels (4, 8, and 12%) of weight percent (wt%) of Sr powder. The findings show that the surface hardness increases on increasing the Sr content in HA, whereas the surface roughness tends to decrease on Sr increment. The bare Ti13Nb13Zr substrate shows hydrophobic behavior while all the coated substrates are hydrophilic and give rise to the improved clinical performance of the implant. The electrochemical study showed that HA/Sr coated substrates possesses higher corrosion resistance than bare and pure HA-coated titanium substrate. The outcomes of this study indicated that the Ti13Nb13Zr alloy plasma-sprayed with HA and HA/Sr is beneficial for future bone implant applications. Graphic Abstract: [Figure not available: see fulltext.] © 2021, The Author(s), under exclusive licence to The Materials Research Society.
The biocompatibility and bioactivity properties of hydroxyapatites (HAs) modified through lithium addition were investigated. Hydroxyapatites obtained from bovine bone were mixed with lithium carbonate (Li), in the proportions of 0.25, 0.50, 1.00, and 2.00% wt, and sintered at 900 • , 1000 • , 1100 • , 1200 • , and 1300 • C, creating LiHA samples. The osteoblast culture behavior was assessed in the presence of these LiHA compositions. The cellular interactions were analyzed by evaluating the viability and cellular proliferation, ALP production and collagen secretion. The cytotoxic potential was investigated through measurement of apoptosis and necrosis induction. The process of cellular attachment in the presence of the product of dissolution of LiHA, was evaluated trough fluorescence analysis. The physical characteristics of these materials and their cellular interactions were examined with SEM and EDS. The results of this study indicate that the LiHA ceramics are biocompatible and have variable bioactivities, which can be tailored by different combinations of the concentration of lithium carbonate and the sintering temperature. Our findings suggest that LiHA 0.25% wt, sintered at 1300 • C, combines the necessary physical and structural qualities with favorable biocompatibility characteristics, achieving a bioactivity that seems to be adequate for use as a bone implant material.
Strontium doped hydroxyapatite (Sr-doped HA) nanopowder has been synthesized using a sol-gel method. The concentration of strontium was varied at 2, 5, 10 and 15 mol%. The as synthesized powders were calcined at temperatures of 500-900°C. The calcined white Sr-doped HA powders were characterized using differential and thermogravimetric analysis (TG/DTA), field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). Morphological evaluation by FESEM measurement shows that the particles of the Sr-doped HA agglomerates are globular in shape with an average size of 1-2 mm in diameter while the primary particles have a diameter of 30-150 nm in average. The calcined powders contained hydroxyapatite phase only for all doping concentration except for the smallest doping concentration, 2 mol%, where â-TCP appeared as the secondary phase. This indicates that the substitution of Sr atoms for Ca atoms have stabilized the HA phase, leading to the inhibition of the appearance of â-TCP phase upon high temperature calcination. Even, for 2 mol% Sr-doped HA, the appearance of â-TCP peak only started to appear at a temperature as high as of 900°C, compared to non-Sr doping HA which appeared at a temperature below 800°C.
In this study, strontium-doped calcium phosphate coatings were deposited by electrochemical deposition and plasma spray under different process parameters to achieve various coating morphologies. The coating composition was investigated by energy dispersive X-ray spectroscopy and X-ray diffraction. The surface morphologies of the coatings were studied through scanning electron microscopy while the cytocompatibility and bioactivity of the strontium-doped calcium phosphate coatings were evaluated using bone cell culture using MC3T3-E1 osteoblast-like cells. The addition of strontium leads to enhanced proliferation suggesting the possible benefits of strontium incorporation in calcium phosphate coatings. The morphology and composition of deposited coatings showed a strong influence on the growth of cells.
Infection in primary total joint prostheses is estimated to occur in up to 3% of all surgery. As a measure to improve the antimicrobial properties of implant materials silver (Ag) was incorporated into plasma sprayed hydroxyapatite (HA) coatings. To offset potential cytotoxic effects of Ag in the coatings strontium (Sr) was also added as a binary dopant. HA powder was doped with 2.0 wt.% Ag(2)O, 1.0 wt.% SrO and was then heat treated at 800 °C. Titanium substrates were coated using a 30 kW plasma spray system equipped with a supersonic nozzle. X-ray diffraction confirmed the phase purity and high crystallinity of the coatings. Samples were evaluated for mechanical stability by adhesive bond strength testing. The results show that the addition of dopants did not affect the overall bond strength of the coatings. The antibacterial efficacies of the coatings were tested against Pseudomonas aeruginosa. Samples that contained the Ag(2)O dopant were found to be highly effective against bacterial colonization. In vitro cell-material interactions using human fetal osteoblast cells were characterized by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay for cell viability, field emission scanning electron microscopy for cell morphology and confocal imaging for the important differentiation marker alkaline phosphatase (ALP). Our results showed evidence of cytotoxic effects of the Ag-HA coatings, characterized by poor cellular morphology and cell death and nearly complete loss of functional ALP activity. The addition of SrO to the Ag-HA coatings was able to effectively offset these negative effects and improve performance compared with pure HA-coated samples.
Implants of solid sintered hydroxyapatite form very tight bonds with living bone, but are susceptible to fatigue failure. This problem can be overcome by using plasma-sprayed apatite coatings on titanium implants. A very strong bond is formed between bone and this composite material; this was studied in canine bone with plug implants, avoiding any mechanical retention. Mechanical testing showed an interface shear strength at six weeks of 49 MPa with a maximum of 64 MPa after six months. There was histological evidence of direct bonding between the apatite coating and living bone while uncoated control plugs were easily extracted. The results indicate that apatite-coated implants can form a chemical fixation with a strength comparable to that of cortical bone itself. This fixation is far stronger than that provided by current cemented or uncemented fixation techniques.
The growing evidence of the beneficial role of strontium in bone has increased the interest of developing strontium-containing biomaterials for medical applications, and specifically biocompatible coatings that can be deposited on metallic implants to benefit from their load-bearing capabilities. In this work, strontium-substituted hydroxyapatite (Sr-HA) coatings have been fabricated by pulsed laser deposition (PLD) from initial targets obtained after mixing and compacting commercial HA and SrCO3 powders in different proportions. The films thus fabricated were then structurally, morphologically and chemically characterized using scanning electron microscopy, optical profilometry, X-ray diffraction, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy and energy dispersive X-ray spectroscopy. The macroscopic morphology of the films presented in all cases equivalent spherical shaped aggregates of typical calcium phosphate coatings. The results reveal, however, the incorporation of Sr2+ and carbonate groups in the coatings as a function of the SrCO3 content in the ablation target, being the incorporation of Sr2+ a linear phenomenon that is accompanied by a similarly linear withdrawal of Ca2+. The role of Sr2+ in the modification of the HA structure and a possible mechanism of substitution of Sr2+ atoms in place of Ca2+ atoms are discussed.
RF magnetron sputtering of calcium phosphate (CaP) thin films has been shown to offer significant advantages over other deposition techniques due to the fact that it can offer significant control over the processing condition. Specifically, this technique allows the properties of the deposited coatings to be tailored by varying either the target composition or the in-situ processing parameters. This novel work presents the results from a detailed study of the coatings created by co-sputtering from three targets with different Ca/P ratios. Target combinations were chosen from hydroxyapatite (HA), α tri-calcium phosphate (TCP) and di-calcium phosphate (DCP), with average target stoichiometries of between 1.0 and 1.67 before sputtering. The target combinations chosen provide scope in relation to control of the CaP surface properties than those previously available. The samples have been analysed both in the as-deposited state and after thermal annealing to 500 °C using Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS). As-deposited coatings were all amorphous in nature, as confirmed by FTIR and XRD analyses. The Ca/P ratios of the as-deposited coatings were generally below those of the average starting target stoichiometry. This was not unexpected for the processing conditions employed here. However, after thermal processing, most of the coatings produced were shown to be crystalline, with an observed increase in the coating Ca/P ratios. However, the coating with an average starting Ca/P ratio of 1.22 did not see any enhancement in its crystallinity. The results from this study show how the varying target compositions control both the annealed coating's stoichiometry and crystallinity, with all coatings also displaying varying levels of preferred orientation. Therefore, the results described here provide a route to control the properties of a CaP surface to meet the requirements of the user, with specific emphasis on critical parameters such as phase, crystallinity and stoichiometry.
Strontium is used orally in the medical treatment of osteoporosis because of its stimulative effect on bone formation and, simultaneously, its inhibiting effect on bone resorbing cells. Due to these effects, it might also be used for calcium phosphate-based bone substitutes. We hypothesise that strontium-substituted hydroxyapatite can be synthesised using a wet chemical reaction and a subsequent thermal treatment. Up to 15 wt% of strontium was successfully incorporated into the lattice of hydroxyapatite without affecting the apatite structure. Higher concentrations led to a destabilisation of the structure and the formation of beta-tricalcium phosphate as a secondary phase. The bending strength of the composite materials was up to 30 MPa, independent of the strontium content. Initial cell culture experiments proved the cytocompatible behaviour of the material. We therefore conclude that strontium-substituted hydroxyapatite can be synthesised with suitable biological and mechanical properties as potential bone substitute material for osteoporotic patients.
Pure and doped hydroxyapatite (HA) nanocrystalline powders (Ca10-xMgx(PO4)6OH2) were synthesized using sol-gel process. For this, calcium nitrate tetrahydrate, magnesium nitrate hexahydrate, and phosphorous pentoxide were used as precursors for Ca, Mg, and P, respectively. Calculated amounts of magnesium ions (Mg+2) especially from 0 to 10% (molar ratio) were incorporated as dopant into the calcium sol solution. The structure and morphology of the gels obtained after mixing the phosphorous and (calcium + magnesium) sol solution were different, and their condensations in time depend on the quantities of magnesium added. The several powders resulting from the gels dried and sintered at 500°C for 1 h were characterized by thermogravimetry (TG), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and inductively coupled plasma (ICP). Additionally, their agglomeration, morphology, and particle size were investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The specific surface area of each sample was measured by the Brunauer–Emmett–Teller (BET) gas adsorption technique. The results of XRD, FTIR, and ICP values ranged between 0.45 and 2.11 mg/L indicated that the magnesium added in the calcium solution was incorporated in the lattice structure of HA so prepared, while those obtained by SEM and TEM confirmed the influence of Mg on their morphology (needle and irregular shape) and crystallite size, which is about 30–60 nm. The as-prepared powders had a specific surface area ranged between 6.37 and 27.60 m2/g.
In the present study, synthesis of monophasic Sr-HAp nanocrystals using a single step Solution Combustion Synthesis (SCS) process is reported. Effects of important process parameters on the formation of monophasic Sr-HAp nanocrystals were investigated to optimize the process for cost effective synthesis. X-ray Diffraction (XRD) and transmission electron microscopy (TEM) studies of as-synthesized powders (Sr ranging from 0 to 30%) revealed close packed hexagonal structure, with individual primary particle sizes ranging from 15 to 70 nm length and 5 ± 1 nm diameter. Scanning Electron Microscopy (SEM) studies showed that Sr substitution in HAp increased the aspect (L/D) ratio of primary nanorod and reduced the secondary agglomerate coarsening. Fourier Transform-Infrared (FTIR) and Energy Dispersive Spectroscopy (EDS) studies confirmed the presence of appropriate concentrations of phosphates and hydroxyl groups along with small amounts of carbonates in the as-synthesized Sr-HAp. Differential Scanning Calorimetry (DSC) studies up to 400 °C and XRD patterns of powders calcined at 1100 °C proved that Sr addition in HAp enhances the stability by suppressing the phase transformation during further consolidation. In effect, nano Sr-HAp powders synthesized using SCS process resembled the structural and chemical nature of bone mineral and could be used as a possible candidate material for hard tissue replacement and drug delivery systems.
To obtain an Sr-substituted hydroxyapatite thin film, sputter-coating was performed on a cellulose filter acting as a substrate from the mixture target of hydroxyapatite (HA) and strontium-apatite (SrAp) at an Ar pressure of 0.5–5.0 Pa. The ratio of the SrAp in the mixture target was varied from 25% to 100%. After coating, the films were heated at 700 °C to remove the cellulose filter substrate, and the crystalline phases were identified by X-ray diffraction (XRD). The sputter-coated film was identified as the Sr-substituted β-tri-calcium phosphate (TCP) and the Sr-substituted β-calcium pyrophosphate (CPP) as well as the Sr-substituted HA. The weight ratio of the Sr-substituted HA decreased with increasing Ar pressure or with an increasing ratio of SrAp to HA in the target. The average Sr/(Ca + Sr) molar ratio in the film was 1.9%–3.5% slightly lower than the initial SrAp ratio of the target, and the ratio was not influenced by the Ar pressure. In the (Sr + Ca)/P ratio, the ratio decreased while increasing the SrAp ratio in the target.
Zinc oxide thin films have been grown on c-cut (0001) and r-cut (1 1¯ 0 2) sapphire substrates by pulsed-laser deposition using a Nd:YAG laser operating at 355nm in picosecond regime (pulse duration: 42ps). The composition and the structural properties of the films have been investigated by scanning electron microscopy, Rutherford backscattering spectroscopy and X-ray diffraction according to different substrate temperatures. The RBS spectra show a Zn/O ratio close to 1.1 with a constant in-depth oxygen concentration. The XRD diagrams in Bragg–Brentano geometry display a preferred orientation depending on the used substrate. The large width of XRD peaks is indicative of a small coherence length. In addition, according to the pole figures recorded in asymmetric configuration, epitaxial relationships between substrate and film are evidenced. An increase in the substrate temperature leads to a film crystalline quality improvement. The results are discussed regarding the well-known properties of ZnO films obtained by nanosecond and femtosecond PLD.
We report the first quasi-elastic neutron scattering analysis of proton mobility in the solid electrolyte CaHPO4·2H2O (brushite). We have studied this hydrated phosphate, in powder state, from 190 to 520 K, using an incident wavelength of 5.12 Å. The time of flight spectra are converted inS(Q,ω) structure factor and inelastic frequency distributionP(Q,ω) in the energy range 0–200 meV (0–1600 cm)−1. A quasi-elastic contribution is clearly evidenced above room temperature; it is fitted with a jump model, involving hydrogen bonds. The quasi-elastic and inelastic scattering data are compared with FTIR results. Two kinds of motions are determined: jumps of acidic protons on hydrogen bonds and vibrations of lattice water molecules associated with the motion of their hydrogen atom on hydrogen bonds (Ea≈0.145 eV). Above 450 K the dehydration of the compound is accompanied by the appearance of a long-range diffusive motion and by the disappearance of some low-frequency inelastic bands.
There have been a significant advances made in the field of bioceramics, particularly hydroxyapatite (HA) during the past 10years. Emphasis has now shifted towards designing HA with enhanced bioactivity for bone tissue repair. The aim of this study was to assess whether surface wettability can be correlated with cellular interactions with silicon-substituted hydroxyapatite (SiHA)-coated titanium (Ti) substrates. SiHA thin coatings of varying Si compositions were deposited on Ti substrates via a magnetron co-sputtering technique. These coatings were then subjected to an in vitro study using primary human ostoeblast (HOB) cells, to evaluate their biological property. HOB cells showed initial poor adhesion and spreading on hydrophobic Ti surface. The application of HA or SiHA thin coatings on Ti substrates by magnetron co-sputtering technique renders the surface more hydrophilic, with water contact angles between 30 and 40°. HOB cells attached, spread and proliferated well on these coatings. Enhanced calcification (formation of calcium phosphate nodules across the collagenous matrices) was observed on SiHA coatings with increasing Si content. This interdisciplinary paper highlighted that enhanced bioactivity was associated with surface wettability. Producing a nanostructured HA coating on a Ti substrate by magnetron sputtering resulted in the promotion of cell proliferation and calcification, and the latter was further enhanced with Si substitution. Hence, SiHA thin coating holds great potential as an alternative dental material.
An amorphous calcium phosphate (ACP) is easily prepared by precipitation from alkaline solution but at acid pH, crystalline phases normally form directly. This investigation shows that ACPs can also be prepared at acid pH provided a stabiliser is used. Magnesium ions or citrate stabilised ACPs prepared at pH 6.5 but at pH 6.0 only citrate was effective. The new ACPs differed in chemical composition and infrared spectrum from the conventional ACP but the short-range environment about calcium ions, as measured by EXAFS spectroscopy, was very similar in all the ACPs. We suggest that ACPs can form from any highly supersaturated solution provided the nucleation and growth of all crystalline phases is inhibited.
Since many orthopedic implants fail as a result of loosening, wear, and inflammation caused by repeated loading on the joints, coatings such as hydroxyapatite (HAp) on titanium with a unique topography have been shown to improve the interface between the implant and the natural tissue. Another serious problem with long-term or ideally permanent implants is infection. It is important to prevent initial bacterial colonization as existing colonies have the potential to become encased in an extracellular matrix polymer (biofilm) that is resistant to antibacterial agents. In this study, plasma-based ion implantation was used to examine the effects of pre-etching on plain titanium. Topographical changes to the titanium samples were examined and compared via scanning electron microscopy. Hydroxyapatite and silver-doped hydroxyapatite thin films were then sputter deposited on titanium substrates etched at − 700 eV. For silver-doped films, two concentrations of silver (~ 0.5 wt.% and ~ 1.5 wt.%) were used. Silver concentrations in the film were determined using energy dispersive X-ray spectroscopy. Hydroxyapatite film thicknesses were determined by measuring the surface profile using contact profilometry. Staphylococcus epidermidis and Pseudomonas aeruginosa adhesion studies were performed on plain titanium, titanium coated with hydroxyapatite, titanium coated with ~ 0.5 wt.% silver-doped hydroxyapatite, and titanium coated with ~ 1.5 wt.% silver-doped hydroxyapatite. Results indicate that less bacteria adhered to surfaces containing hydroxyapatite and silver; further, as the hydroxyapatite films delaminated, silver ions were released which killed bacteria in suspension.
Fluorapatite (FAP) and hydroxyapatite (HAP) were prepared and doped with potassium fluoride. KF/FAP and KF/HAP were prepared by usual impregnating method. The doped materials were characterised by X-ray diffraction, BET surface area, BJH total pore volume and scanning electron microscopy (SEM). All this data were compared to that of unimpregnated apatites. Some modifications in the particles morphology were observed by doping apatites with KF. The comparison of the catalytic activity of KF, FAP, HAP, KF/FAP and KF/HAP indicate clearly the positive effect of the doping apatites by KF in the Knoevenagel condensation used as model reaction. In this work, KF/FAP and KF/HAP were prepared and used for the first time as new and efficient catalysts in heterogeneous solid–liquid synthesis.
To achieve a good bioactivity, magnetron-sputtered (MS) hydroxyapatite (HA) coatings have to be stoichiometric and crystalline. It has also been suggested that doping HA with metallic elements improves its bioactivity but frequently reduces its Young's modulus. Therefore, efforts are still necessary to identify adequate growth conditions, good doping elements and finally to grow doped HA films. In a first attempt, HA films have been synthesized by MS. Our conditions enabled us to grow at 10 nm min-1 stoichiometric and crystallized HA coatings that presented a strong texture. The latter is discussed in view of the competitive growth of the material under the strong electron and ion bombardments used here. Based on ab initio calculations identifying Ta as a promising doping element, we then investigated the growth of Ta-doped hydroxyapatite (HA:Ta) by magnetron co-sputtering. The HA:Ta films were in situ crystallized. Our data reveals that for Ta contents 4.5 at.%, Ta could substitute Ca in the HA cell. For higher doping contents, a deviation from the stoichiometric compound is observed and CaO appears. By nanoindentation, we have measured an elastic modulus of 120 9 GPa for a Ta content of 3 at.%. This value is very close to the value of 110 GPa calculated by ab initio calculations, supporting the substitution scenario. The elasticity drop may be understood by screening of the ionic interaction between constituents in HA upon Ta incorporation. 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Investigations of the electronic structures of substituted strontium apatites were carried out by using X-ray photo electron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction technique (XRD) has been used to determine the structural parameters. Electron microprobe microanalysis technique was used to estimate the elemental concentrations in each substituted apatite material. The present work aims at studying the changes in the electronic structure of Sr5(PO4)3OH (Sr-HAP) upon isomorphic substitution by F and Cl at the OH site of apatite and Sr by Na at trans Sr-HAP. The ion exchange between Na+ in sodium alginate and aqueous Ca2+ was important for the preparation of calcium hydroxyapatite. In contrast, the reaction of sodium alginate with the mixture of Na4P2O7 and aqueous Sr2+ afforded strontium hydroxyapatite at the specific ratio. The structure of calcium and strontium phosphates prepared from the sol–gel process evidently depended on the amount of sodium alginate introduced into the mixture of Na4P2O7 and the corresponding divalent cations. The findings have ensured that substitution of Sr-HAP by Na enhances the binding energy of O and Sr core levels. It was also noticed that the same substitution decreases the binding energy of P 2s-level. These observations point out to a decrease in the electron density at P and an increase in the electron density at O in Sr atoms.
The initial behaviour and ultimately the long-term performance of calcium phosphate (Ca–P) coatings for hard tissue implant applications are influenced by their dissolution properties. For this study, Ca–P coatings were deposited onto Ti-6Al-4V substrates using RF magnetron sputtering. The physico-chemical nature of these deposited layers was then determined both before and after annealing at 400 °C using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Furthermore, their dissolution behaviour in phosphate buffered saline (PBS) solution was also examined using similar techniques. The data shows clearly that the as-deposited coatings are amorphous when compared with the more crystalline coatings produced after annealing at 400 °C. These as-deposited coatings completely dissolve after exposure to the PBS for only 24 h; however, the dissolution rate of the annealed coatings is more restrained. Whereas the XPS and FTIR data show no change in the chemical nature of the annealed coatings after 30 days, the AFM results reveal subtle changes in the surface topography of the coatings after only 1 h of immersion. These data clearly show the utility of surface analytical techniques, such as AFM in combination with more established techniques for examining the surface properties of Ca–P coatings. Furthermore, the study also shows that calcium phosphate coatings deposited at low power using RF magnetron sputtering can undergo a decreased dissolution rate under physiological conditions they when subjected to post deposition annealing.
The clinical use of plasma-sprayed hydroxyapatite (HA) coatings on metal implants has aroused as many controversies as interests over the last decade. Although faster and stronger fixation and more bone growth have been revealed, the performance of HA-coated implants has been doubted. This article will initially address the fundamentals of the material selection, design, and processing of the HA coating and show how the coating microstructure and properties can be a good predictor of the expected behavior in the body. Further discussion will clarify the major concerns with the clinical use of HA coatings and introduce a comprehensive review concerning the outcomes experienced with respect to clinical practice over the past 5 years. A reflection on the results indicates that HA coatings can promote earlier and stronger fixation but exhibit a durability that can be related to the coating quality. Specific relationships between coating quality and clinical performance are being established as characterization methods disclose more information about the coating. © 2001 John Wiley & Sons, Inc. J Biomed Mater Res (Appl Biomater) 58: 570–592, 2001
There is growing evidence that strontium ranelate (SR; S12911-2, PROTELOS; Institut de Recherches Internationales Servier, Courbevoie, France), a compound containing 2 atoms of stable strontium (Sr), influences bone cells and bone metabolism in vitro and in vivo. We previously reported that SR increases bone mass in rats and mice by stimulating bone formation and inhibiting bone resorption. We also showed that short-term treatment with SR enhances osteoblastic cell recruitment and function in short-term rat calvaria cultures. Because Sr incorporates into the bone matrix, it was of interest to determine whether SR may affect matrix mineralization in long-term culture. To this goal, osteogenic mouse calvaria-derived MC3T3-E1 osteoblastic cells were cultured for up to 14 days in the presence of ascorbic acid and phosphate to induce matrix formation and mineralization. Matrix formation was determined by incorporation of tritiated proline during collagen synthesis. Matrix mineralization was quantified by me
Hydroxyapatite powders characterized by ionic substitutions both in anionic and cationic sites were successfully prepared by synthesis in aqueous medium. The process parameters were set up to allow the simultaneous substitution of the foreign ions, namely carbonate, magnesium and silicon in the crystallographic site of calcium and phosphorus, keeping in count the competition which arises between atoms destined to occupy the same crystallographic site.The chemico-physical properties of the powders were investigated through several analytical techniques, i.e. X-ray diffraction, infrared spectroscopy, atomic emission spectroscopy and thermo-gravimetric analysis. The results show that the utilization of sodium hydrogen-carbonate as a reactant allows the entering of carbonate into the HA structure, mainly in phosphate position, while sodium is eliminated during the process of the powder washing. The entering of silicon in the HA structure progressively reduces its crystallinity, as also carbonate ions do. Silicate and carbonate ions can enter simultaneously into the HA structure, in biological-like amounts, although they compete for the occupation of the phosphate site; the powder crystallinity is strongly reduced as the content of the two substituting ions increases, so that a limit molar concentration exists where the apatite structure collapses and an amorphous phase forms with the simultaneous formation of crystalline calcium carbonate. Solubility tests, carried out at physiological conditions, reveal an increased calcium release in the HA powders containing silicon compared to the silicon-free HA; the solubility behaviour of the multi-substituted HA powders at physiological conditions makes these materials promising as bioactive bone scaffold, as they are able to continuously supply ions which are essential for the process of bone reconstruction.
Antimicrobial materials based on hydroxyapatite are potentially attractive in a wide variety of medical applications. The synthesis of copper and zinc-doped hydroxyapatite was done by neutralization method. This method consists of dissolving CuO or ZnO in solution of H3PO4, and the slow addition to suspension of Ca(OH)2 for obtaining monophasic product. Characterization studies from XRD, SEM, TEM and FTIR spectra showed that particles of all samples are of nano size and they do not contain any discernible crystalline impurity. The quantitative elemental analysis showed that the copper and zinc ions fully incorporated into the hydroxyapatite. The antimicrobial effects of doped hydroxyapatite powders against pathogen bacterial strains Escherichia coli, Staphylococcus aureus and pathogen yeast Candida albicans were tested in solid and liquid media. Quantitative test in liquid media clearly showed that copper and zinc-doped samples had viable cells reduction ability for all tested strains.
A crystalline solid that is a special form of the mineral apatite dominates the composite material bone. A mineral represents the intimate linkage of a three-dimensional atomic structure with a chemical composition, each of which can vary slightly, but not independently. The specific compositional–structural linkage of a mineral influences its chemical and physical properties, such as solubility, density, hardness, and growth morphology. In this paper, we show how a mineralogic approach to bone can provide insights into the resorption–precipitation processes of bone development, the exceedingly small size of bone crystallites, and the body's ability to (bio)chemically control the properties of bone. We also discuss why the apatite phase in bone should not be called hydroxylapatite, as well as the limitations to the use of the stoichiometric mineral hydroxylapatite as a mineral model for the inorganic phase in bone. This mineralogic approach can aid in the development of functionally specific biomaterials.
Calcium phosphate (hydroxyapatite and tri-calcium phosphate) bioceramics closely resembling, in chemical composition, those found in vivo in human bones have been synthesized by using novel synthetic body fluid solutions via the self-propagating combustion synthesis (SPCS) method. Powder characterization was performed by XRD, ICP-AES, FTIR and SEM.
Calcium phosphates such as hydroxyapatite have a wide range of applications both in bone grafts and for the coating of metallic implants, largely as a result of their chemical similarity to the mineral component of bone. However, to more accurately mirror the chemistry, various substitutions, both cationic (substituting for the calcium) and anionic (substituting for the phosphate or hydroxyl groups) have been produced. Significant research has been carried out in the field of substituted apatites and this paper aims to summarise some of the key effect of substitutions including magnesium, zinc, strontium, silicon and carbonate on physical and biological characteristics. Even small substitutions have been shown to have very significant effects on thermal stability, solubility, osteoclastic and osteoblastic response in vitro and degradation and bone regeneration in vivo.
Octacalcium phosphate (OCP) is a promising alternative to hydroxyapatite as biomaterial for hard tissue repair. In this study we successfully applied Matrix Assisted Pulsed Laser Evaporation (MAPLE) to deposit Mg and Sr doped OCP (MgOCP and SrOCP), as well as OCP, thin films on titanium substrates. OCP, Mg-substituted and Sr-substituted OCP were synthesized in aqueous medium, then were suspended in deionised water, frozen at liquid nitrogen temperature and used as targets for MAPLE experiments. The depositions were carried out using a KrF* excimer laser source (λ=248 nm, τ(FWHM)=25 ns) in mild conditions of temperature and pressure. The results of X-ray diffraction, infrared spectroscopy, scanning electron microscopy and energy dispersive spectroscopy investigations revealed that the OCP thin films are deposited in the form of cauliflower-like aggregates and droplets, as well as crystal fragments, with a homogeneous distribution of magnesium and strontium on the surface of the coatings. Human osteoblast-like MG-63 cells were cultured on the different biomaterials up to 14days. MgOCP and SrOCP coatings promote osteoblast proliferation and differentiation with respect to OCP. Under these experimental conditions, the production of procollagen-type I, transforming growth factor-β1, alkaline phosphatase and osteocalcin indicated that the level of differentiation of the cells grown on the different coatings increased in the order OCP<MgOCP<SrOCP.
This study attempts to enhance the osseointegration of titanium implants by adopting a micro-arc treatment (MAT) capable of replacing calcium (Ca) with different percentages of strontium (Sr) in order to fabricate strontium-containing hydroxyapatite (Sr-HAp) coatings. Sr, regarded as a significant therapy promoting bone mass and bone strength, has a dual mechanism, enhancing osteoblast differentiation and inhibiting osteoclast differentiation. This study also investigates how Sr content affects the microstructure of and osteoblast/osteoclast growth on the coatings. Experimental results indicate that an increase in the Sr content in the electrolyte bath results in a greater degree of Sr substitution at Ca sites within the HAp phase, facilitating the formation of Sr-HAp coatings with Sr fully solid soluble in the HAp phase. Irrespective of the Sr content, most coatings are similar in porous morphology and pore size. Additionally, the Sr-HAp coating shows higher osteoblast compatibility than raw titanium metal and the HAp coating. Moreover, cell adhesion and proliferation after 48 h was greater than that after 4 h, indicating that Sr can stimulate osteoblast adhesion and proliferation. Further, Sr significantly inhibits osteoclast differentiation when the Sr-HAp coatings exceed 38.9 at.% Sr.
Strontium (Sr) plays a special role in bone remodelling, being associated with both the stimulation of bone formation and a reduction in bone resorption. Thus, the modification of biomaterials by partial or full substitution by Sr is expected to increase both bioactivity and biocompatibility. However, such effects have to be studied individually. Although no phase transition was found in Sr-substituted hydroxyapatite (Sr-HA), Sr-containing calcium silicate (Sr-CS) or Sr-containing borosilicate (Sr-BS), their biological performance was substantially affected by changes in the physico-chemical properties and Sr content of the materials. Three distinct outcomes were found for the presence of Sr: (1) increased HA solubility; (2) no significant effect on the degradation rate of CS; (3) apparent inhibition of the otherwise rapid degradation of BS. In each case the released Sr affected osteoblast proliferation and alkaline phosphatase activity, with clear evidence that an optimum Sr dose exists. Such chemical and biological variations must be disentangled for the behaviour to be properly understood and materials design to be advanced.
This study was designed to investigate the effects of strontium-substituted hydroxyapatite coatings with 10 mol% Ca(2+) replaced by Sr(2+) (10% SrHA) on implant fixation in ovariectomized (OVX) rats. Coatings of HA and 10% SrHA were prepared on the surface of titanium implant using sol-gel dip methods, and then characterized by Scanning Electron Microscope, Atomic Force Microscope, X-ray diffraction, X-ray Photoemission Spectroscopy, and an automatic scratch tester. Twelve weeks after bilateral ovariectomy, twenty OVX rats accepted implant insertion in the proximal tibiae, half with HA-coated implants and the other half with 10% SrHA coated implants. After 12-week healing period, 10% SrHA coated implants revealed improved osseointegration compared to HA, with the bone area ratio and bone-to-implant contact increased by 70.9% and 49.9% in histomorphometry, the bone volume ratio and percent osseointegration by 73.7% and 45.2% in micro-CT evaluation, and the maximal push-out force and ultimate shear strength by 107.2% and 132.9% in push out test. These results demonstrated that 10% SrHA coatings could enhance implant osseointegration in OVX rats, and suggested the feasibility of using SrHA coatings to improve implant fixation in osteoporotic bone.
A series of doped apatites have been deposited onto titanium (V) substrates using a novel ambient temperature blasting process. The potential of these deposited doped apatites as non-colonizing osteoconductive coatings has been evaluated in vitro. XPS, EDX, and gravimetric analysis demonstrated that a high degree of coating incorporation was observed for each material. The modified surfaces were found to produce osteoblast proliferation comparable to, or better than, a hydroxyapatite finish. Promising levels of initial microbial inhibition were observed from the Sr- and Ag-doped surfaces, with the strontium showing prolonged ability to reduce bacteria numbers over a 30-day period. Ion elution profiles have been characterized and linked to the microbial response and based on the results obtained, mechanisms of kill have been suggested. In this study, the direct contact of coated substrate surfaces with microbes was observed to be a significant contributing factor to the antimicrobial performance and the anticolonizing activity. The silver substituted apatite was observed to out-perform both the SrA and ZnA in terms of biofilm inhibition.
Owing to its resemblance to the major inorganic constituent of bone and tooth, hydroxyapatite is recognized as one of the most biocompatible materials and is widely used in systems for bone replacement and regeneration. In this study the pulsed laser deposition technique was chosen to produce hydroxyapatite with different crystallographic orientations in order to investigate some of the material properties, including its in vitro dissolution behavior, as well as mechanical properties. The crystallographic orientations of hydroxyapatite coatings can be carefully controlled, mainly by varying the energy density of the KrF excimer laser (248 nm) used for deposition. Nanoindentation results showed that highly c-axis oriented hydroxyapatite coatings have higher hardness and Young's modulus values compared with the values of randomly oriented coatings. After 24h immersion in simulated physiological solution the overall surface morphology of the highly oriented coatings was dramatically altered. The porosity was drastically increased and sub-micron pores were formed throughout the coatings, whereas the average size of the grains in the coatings was not significantly changed. The composition of the textured hydroxyapatite coatings remained essentially unchanged. Their c-axis texture, on the other hand, was rather enhanced with an increase in immersion time. The c-axis oriented hydroxyapatite surfaces are likely to promote preferentially oriented growth through a cyclic process of dissolution and reprecipitation, followed by homoepitaxial growth. The remarkable morphological and microstructural changes after dissolution suggest a capability of highly textured hydroxyapatite as a tissue engineering scaffold with an interconnecting porous network that may be beneficial for cellular activity.
Bone mineral is a multi-substituted calcium phosphate. One of these ion substitutions, strontium, has been proven to increase bone strength and decrease bone resorption. Biomimetics is a potential way to prepare surfaces that provide a favorable bone tissue response, thus enhancing the fixation between bone and implants. Here we prepared double-layered strontium-substituted apatite and titanium dioxide coatings on titanium substrates via mimicking bone mineralization. Morphology, crystallinity, surface chemistry and composition of Sr-substituted coatings formed via biomimetic coating deposition on crystalline titanium oxide substrates were studied as functions of soaking temperature and time in phosphate buffer solutions with different Sr ion concentration. The morphology of the biomimetic apatite changed from plate-like for the pure HA to sphere-like for the Sr ion substituted. Surface analysis results showed that 10-33% of Ca ions in the apatite have been substituted by Sr ions, and that the Sr ions were chemically bonded with apatite and successfully incorporated into the structure of apatite.
The substitution of Zn in hydroxyapatite (HA) crystals was examined via comprehensive characterization techniques. Nanosized HA crystals were synthesized by the wet chemical method in aqueous solutions including various amounts of Zn ions. X-ray fluorescent spectroscopy was used to examine the amount of Zn in the HA precipitates. Scanning electron microscopy and high-resolution transmission electron microscopy were employed to examine the effects of Zn on the morphology and crystal size of the precipitates. Conventional powder X-ray diffraction and the Rietveld refinement method revealed the apatite lattice parameters and phase changes with the inclusion of Zn. The results indicated that Zn ions partially substituted for Ca ions in the apatite structure. They were not simply adsorbed on the apatite surface or in the amorphous phase. The precipitates maintained the apatite phase up to a Zn:(Zn+Ca) ratio of 15-20 mol.% in the solution. Pure HA was well crystallized and the crystals had regular shapes, whereas the Zn-substituted apatite crystals became irregular and formed agglomerates. The lattice parameters, a and c, decreased at a Zn:(Zn+Ca) ratio of 10 mol.%.
A novel Sr-containing calcium phosphate cement (CPC) with excellent compressive strength, good radiopacity and suitable setting time was developed in this work. The two-step hydration reaction resulted in a high compressive strength, with a maximum of up to 74.9MPa. Sr was doped into the calcium-deficient hydroxyapatite as a hydrated product during the hydration reaction of the CPC. Because of the existence of Sr element and the compact microstructure after hydration, the Sr-containing CPC shows good radiopacity. It is expected to be used in orthopedic and maxillofacial surgery for bone defects repairing.
B-type carbonated hydroxyapatites, prepared in aqueous media free of alkali ions, fix ammonium ions present in the reaction medium. A small portion of the carbonate ions introduced into the apatite structure enter by the substitution mechanism (CO
32−, NH
4+)→(PO
43−, Ca2+). With these results for the structural incorporation of ammonium ions, differences in lattice parameters observed among specimens with the same degree of carbonation were attributed to some substitution of NH
4+ for Ca2+. The fixed ammonium ions were shown to be the source of the cyanamide and cyanate ions that develop on heating. Above 500°C these apatites lost both the carbonate and the cyanate and cyanamide ions.
The clinical use of plasma-sprayed hydroxyapatite (HA) coatings on metal implants has aroused as many controversies as interests over the last decade. Although faster and stronger fixation and more bone growth have been revealed, the performance of HA-coated implants has been doubted. This article will initially address the fundamentals of the material selection, design, and processing of the HA coating and show how the coating microstructure and properties can be a good predictor of the expected behavior in the body. Further discussion will clarify the major concerns with the clinical use of HA coatings and introduce a comprehensive review concerning the outcomes experienced with respect to clinical practice over the past 5 years. A reflection on the results indicates that HA coatings can promote earlier and stronger fixation but exhibit a durability that can be related to the coating quality. Specific relationships between coating quality and clinical performance are being established as characterization methods disclose more information about the coating.
A novel synthesis route has been developed to produce a high-purity mixed AB-type carbonate-substituted hydroxyapatite (CHA) with a carbonate content that is comparable to the type and level observed in bone mineral. This method involves the aqueous precipitation in the presence of carbonate ions in solution of a calcium phosphate apatite with a Ca/P molar ratio greater than the stoichiometric value of 1.67 for hydroxyapatite (HA). The resulting calcium-rich carbonate-apatite is sintered/heat-treated in a carbon dioxide atmosphere to produce a single-phase, crystalline carbonate-substituted hydroxyapatite. In contrast to previous methods for producing B- or AB-type carbonate-substituted hydroxyapatites, no sodium or ammonium ions, which would be present in the reaction mixture from the sodium or ammonium carbonates commonly used as a source of carbonate ions, were present in the final product. The chemical and phase compositions of the carbonate-substituted hydroxyapatite was characterized by X-ray fluorescence and X-ray diffraction, respectively, and the level and nature of the carbonate substitution were studied using C-H-N analysis and Fourier transform infrared spectroscopy, respectively. The carbonate substitution improves the densification of hydroxyapatite and reduces the sintering temperature required to achieve near-full density by approximately 200 degrees C compared to stoichiometric HA. Initial studies have shown that these carbonate-substituted hydroxyapatites have improved mechanical and biologic properties compared to stoichiometric hydroxyapatite.
In order to determine whether 5-[bis(carboxymethyl) amino]-2-carboxy4-cyano-3-thiopheneacetic acid distrontium salt (S12911-2) inhibits bone resorption by acting on the differentiation and/or function of osteoclasts, its effects were assessed on the 1,25-dihydroxyvitamin D(3)-induced expression of carbonic anhydrase II and vitronectin receptor in chicken bone marrow cells, and on the resorbing activity of authentic rat osteoclasts cultured on bone slices. S12911-2 dose-dependently inhibited, after a 6-day exposure, the expression of carbonic anhydrase II and vitronectin receptor in stimulated osteoclasts (46% and 40%, respectively, at 10(-3) M Sr(2+), P<0.05). A pre-incubation of bone slices with S12911-2 induced a dose-dependent inhibition of bone resorbing activity from 32% at 10(-4) M Sr(2+) to 66% at 10(-3) M Sr(2+) (P<0.05 in each case). A continuous incubation (10(-3) M Sr(2+)) induced a greater inhibition of bone resorbing activity (73%, P<0.05). The inhibition of bone resorption obtained specifically with S12911-2 is related to an inhibition of the differentiation and resorbing activity of the osteoclasts.
For the synthesis of hydroxyapatite crystals from aqueous solutions three preparation methods were employed. From the experimental processes and the characterization of the crystals it was concluded that aging and precipitation kinetics are critical for the purity of the product and its crystallographic characteristics. The authentication details are presented along with the results from infrared spectroscopy, X-ray powder diffraction, Raman spectroscopy, transmission and scanning electron photographs, and chemical analysis. Analytical data for several calcium phosphates were collected from the literature, extensively reviewed, and the results were grouped and presented in tables to provide comparison with the data obtained here.
Using laser Raman microprobe spectroscopy, we have characterized the degree of hydroxylation and the state of atomic order of several natural and synthetic calcium phosphate phases, including apatite of biological (human bone, heated human bone, mouse bone, human and boar dentin, and human and boar enamel), geological, and synthetic origin. Common belief holds that all the studied phases are hydroxylapatite, i.e., an OH-containing mineral with the composition Ca10(PO4)6(OH)2. We observe, however, that OH-incorporation into the apatite crystal lattice is reduced for nanocrystalline samples. Among the biological samples, no OH-band was detected in the Raman spectrum of bone (the most nanocrystalline biological apatite), whereas a weak OH-band occurs in dentin and a strong OH-band in tooth enamel. We agree with others, who used NMR, IR spectroscopy, and inelastic neutron scattering, that-contrary to the general medical nomenclature-bone apatite is not hydroxylated and therefore not hydroxylapatite. Crystallographically, this observation is unexpected; it therefore remains unclear what atom(s) occupy the OH-site and how charge balance is maintained within the crystal. For non-bone apatites that do show an OH-band in their Raman spectra, there is a strong correlation between the concentration of hydroxyl groups (based on the ratio of the areas of the 3572 deltacm(-1) OH-peak to the 960 deltacm(-1) P-O phosphate peak) and the crystallographic degree of atomic order (based on the relative width of the 960 deltacm(-1) P-O phosphate peak) of the samples. We hypothesize that the body biochemically imposes a specific state of atomic order and crystallinity (and, thus, concentration of hydroxyl) on its different apatite precipitates (bone, dentin, enamel) in order to enhance their ability to carry out tissue-specific functions.
The purpose of this study was to investigate the in vivo bone response to the strontium-containing hydroxyapatite (Sr-HA) bioactive bone cement injected into the cancellous bone. Sr-HA cement was injected into the iliac crest of rabbits for 1, 3, and 6 months. Active bone formation and remodeling were observed after 1 month. Newly formed bone was observed to grow onto the bone cement after 3 months. Thick osteoid layer with osteoblasts formed along the bone and guided over the bone cement surface reflected the stimulating effect of Sr-HA. From scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) analysis, high calcium and phosphorus levels were detected at the interface with a thick layer of 70 microm in width, and fusion of Sr-HA with the bone was observed. Blood vessels were found developing in remodeling sites. The affinity of bone on Sr-HA cement was increased from 73.55 +/- 3.50% after 3 months up to 85.15 +/- 2.74% after 6 months (p < 0.01). In contrast to Sr-HA cement, poly(methyl methacrylate) (PMMA) bone cement was neither osteoconductive nor bioresorbable. Results show that the Sr-HA cement is biocompatible and osteoconductive, which is suitable for use in treating osteoporotic vertebral fractures.
Rapid synthesis of calcium deficient hydroxyapatite (CDHA, Ca(10-x)(HPO4)x(PO4)(6-x)(OH)(2-x)) with Ca/P ratio 1.5 was done by precipitation using calcium nitrate tetra-hydrate and phosphoric acid and subsequently subjecting to microwave irradiation in a domestic microwave oven for 15 min. Transmission electron microscopy analysis shows needle like morphology of CDHA having length 16-39 nm and width 7-16 nm. The synthesized CDHA has the characteristic HPO4(2-) vibration band at 875 cm(-1) in Fourier transform infrared (FT-IR) spectra. The X-ray powder diffraction (XRD) analysis shows a pattern corresponding to stoichiometric hydroxyapatite (HA) with broad peaks suggesting that CDHA particles were nanosized. Fourier transform Raman spectroscopy (FT-Raman) do not indicate any fluorescence band that is characteristic of non-stoichiometric HA. The thermal decomposition of CDHA to beta tricalcium phosphate (beta-TCP) was also studied for the additional confirmation. The nanosized CDHA was found to be stable up to 600 degrees C.
The aim of this study was to explore the effect of cerium ions on the formation and structure of hydroxyapatite (HAP). All particles, prepared by hydrothermal method, were synthesized at varied X
Ce = Ce/(Ca + Ce) (from 0 to 10%) with the atomic ratio (Ce + Ca)/P fixed at 1.67. Their morphology, composition and crystal structure were characterized by TEM, EPMA, XRD and FTIR. The results showed that in this composition range the apatite structure is maintained, Ce3 + ions could enter the crystal lattice of apatite and substitute Ca2 + ions. The doping of Ce3 + ions resulted in the decrease of the crystallite size with increase in X
Ce. The HAP particles without doping were short rods having a diameter from 10 to 20 nm and a length from 30 to 50 nm. They grew into long needles upon increasing X
Ce.
A review of the laboratory and clinical data for a new strontium-containing hydroxyapatite bioactive bone cement.
To compare the properties of the strontium-containing bioactive bone cement with those of polymethyl methacrylate (PMMA) and hydroxyapatite (HA) bone cements.
Vertebroplasty and kyphoplasty using conventional PMMA bone cements have been effectively used to treat osteoporotic spine fractures with good short- and medium-term results. However, PMMA has some undesirable properties, including its high setting temperature, lack of osseointegration, and large stiffness mismatch with osteoporotic bone. These properties are responsible for some postoperative complications.
Strontium-containing hydroxyapatite (Sr-HA) bioactive bone cement consists of a filler blend of strontium-containing hydroxyapatite, fumed silica and benzoyl peroxide; and a resin blend of bisphenol A diglycidylether methacrylate, triethylene glycol dimethacrylate, poly(ethylene glycol) methacrylate, and N, N-dimethyl-p-toluidine. Its properties, including mechanical strength, setting temperature, biocompatibility, and osseoinduction, were compared with other cements in vitro and in vivo. Early clinical results are presented.
The Sr-HA cement has a setting time of 15 to 18 minutes, a maximum setting temperature of 58 degrees C, a compressive strength of 40.9 MPa, bending strength of 31.3 MPa, and a bending modulus of 1,408 MPa. The bending strength and modulus are closer to human cancellous bone. Sr-HA cement promotes osteoblast attachment and mineralization in vitro and bone growth and osseointegration in vivo. In a pilot study, 23 cases of osteoporotic fractures treated with this cement with a mean follow-up of 18 months suggest that it is as effective as PMMA in relieving pain.
Oral strontium has been shown to induce new bone formation and is effective in reducing fracture risk in osteoporosis. Our data suggest that strontium delivered locally has the same effect; thus, the combination of strontium with HA in a cement with a low setting temperature, adequate stiffness, and low viscosity makes this a good bioactive cement for vertebroplasty and kyphoplasty.
The purpose of this study was to evaluate the strontium-containing hydroxyapatite (Sr-HA) cement in primary hip replacement, using a rabbit model, and to investigate the histological findings at the cement-implant and bone-cement interfaces under weight-bearing conditions. Unilateral hip replacement was performed with Sr-HA cement or polymethylmethacrylate (PMMA) cement in rabbits and observations were made after 6 months. Good fixation between the Sr-HA cement and implant was observed. Osseointegration of the Sr-HA cement with cancellous bone was widespread. Many multinucleus cells covered the surface of the cement, and resorbed the superficial layer of the cement. By scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) analysis, high calcium and phosphorus levels were detected at the interface with a thickness of about 10 microm. Intimate contact was also observed between the Sr-HA cement and cortical bone without fibrous layer intervening. The overall affinity index of bone on Sr-HA cement was (85.06 +/- 5.40)%, which is significantly higher than that on PMMA cement (2.77%+/- 0.49%). On the contrary, a fibrous layer was consistently observed between PMMA cement and bone, and PMMA cement evoked an inflammatory response and foreign body reaction in the surrounding bony tissues. Results suggested good bioactivity and bone-bonding ability of the Sr-HA cement under weight-bearing conditions.
Bacterial infection after implant placement is a significant rising complication. In order to reduce the incidence of implant-associated infections, several biomaterial surface treatments have been proposed. In this study, the effect of in vitro antibacterial activity and in vitro cytotoxicity of co-sputtered silver (Ag)-containing hydroxyapatite (HA) coating was evaluated. Deposition was achieved by a concurrent supply of 10 W to the Ag target and 300 W to the HA target. Heat treatment at 400 degrees C for 4 h was performed after 3 h deposition. X-ray diffraction, contact angles measurements, and surface roughness were used to characterize the coating surfaces. The RP12 strain of Staphylococcus epidermidis (ATCC 35984) and the Cowan I strain of Staphylococcus aureus were used to evaluate the antibacterial activity of the Ag-HA coatings, whereas human embryonic palatal mesenchyme cells, an osteoblast precursor cell line, were used to evaluate the in vitro cytotoxicity of the coatings. X-ray diffraction analysis performed in this study indicated peaks corresponding to Ag and HA on the co-sputtered Ag-HA surfaces. The contact angles for HA and Ag-HA surfaces were observed to be significantly lower when compared to Ti surfaces, whereas no significant difference in surface roughness was observed for all groups. In vitro bacterial adhesion study indicated a significantly reduced number of S. epidermidis and S. aureus on Ag-HA surface when compared to titanium (Ti) and HA surfaces. In addition, no significant difference in the in vitro cytotoxicty was observed between HA and Ag-HA surfaces. Overall, it was concluded that the creation of a multifunctional surface can be achieved by co-sputtering the osteoconductive HA with antibacterial Ag.
During the last few years Strontium has been shown to have beneficial effects when incorporated at certain doses in bone by stimulating bone formation. It is believed that its presence locally at the interface between an implant and bone will enhance osteointegration and therefore, ensure the longevity of a joint prosthesis. In this study we explore the possibility of incorporating Sr into nano-apatite coatings prepared by a solution-derived process according to an established biomimetic methodology for coating titanium based implants. The way this element is incorporated in the apatite structure and its effects on the stereochemistry and morphology of the resulting apatite layers was investigated, as well as its effect in the mineralization kinetics. By using the present methodology it was possible to incorporate increasing amounts of Sr in the apatite layers. Sr was found to incorporate in the apatite layer through a substitution mechanism by replacing Ca in the apatite lattice. The presence of Sr in solution induced an inhibitory effect on mineralization, leading to a decrease in the thickness of the mineral layers. The obtained Sr-substituted biomimetic coatings presented a bone-like structure similar to the one found in the human bone and therefore, are expected to enhance bone formation and osteointegration.