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Comparative study of structure and properties of thermal spray coatings using conventional and nanostructured hydroxyapatite powder, for applications in medical implants
Abstract
The objective of this paper is to study and compare the structure and properties of thermal spray coatings prepared with conventional and nanostructured hydroxyapatite powder, in order to assess their suitability for future use in medical implants. Four coatings were prepared via Atmospheric Plasma Spray process (APS). Two kinds of feedstock material were employed for the spray process, namely, commercial XPT-D-703 hydroxyapatite powder for half the samples and novel nanostructured PYRO 4 hydroxyapatite powder, which had previously been mechanically treated, for the remaining samples. The substrate of all the samples was stainless steel 304. Finally, the plasma spray parameters were altered for two out of the four coatings, each produced with a different type of powder, in order for a sufficient amount of porosity to be achieved for future incorporation of biomolecules. The coatings were also examined in terms of bioactivity in vitro. It was concluded that the coating produced with the nanostructured powder, under lower plasma energy and at greater spraying distance presented the best results regarding its roughness, bioactive response, crystallinity, adherence and porosity content.
... For orthopaedic implants to survive over the long term, it is crucial to enhance their qualities by reducing the drawbacks. Applying a bioactive material coating to implants is one way to enhance their characteristics and lifespan [3]. ...
Metallic biomaterials have been used to repair and replace human body parts because of their excellent biocompatibility, strong corrosion resistance, and high mechanical properties. A ceramic biomaterial that is highly suitable for coating on metallic biomaterials is hydroxyapatite. This is because it is biocompatible with synthetic and natural bone tissue. There has been a growing interest in HAp-based coatings using thermal spray techniques to enhance the crystallinity and adhesion quality and produce a dense coating of metallic biomaterials. Thermally sprayed coating material has been studied and reviewed in detail in the bioactivity analysis and electro-corrosion analysis. Furthermore, the bioactivity of HAp coatings is determined by their ability to promote bone formation and osseointegration and a valuable understanding of the mechanisms and current advancements in bioactivity. Additionally, the corrosion behaviour of thermally sprayed HAp coatings under simulated conditions has been reviewed.
... Besides, the researchers investigated the behavior of plasma spray coating produced with different-sized HA particles. One of them, conducted by Gkomoza et al. [19], reported that nanostructured HA causes an increase in the crystallinity of the coatings as well as an increase in the thickness of the coatings, which coated 304SS surfaces with both conventional (XPT-D-703) and nanoparticle (PYRO 4) HA by atmospheric plasma spray, as well as dissolve ability of coatings reduced with nanostructures. ...
Nowadays, emphasis on metallic materials, coating materials, and coating technology to improve osseointegration and increase the lifespan of biological fixation prostheses has become a topic of great interest in the field of prosthetic research. Many published studies showed that the bioactivity-coated surfaces increase the implant–tissue compatibility with their similarities to the bone structure. Therefore several coatings are widely used to increase osteoconductivity on implant material surfaces in the biomedical industry. In this section, synthesis techniques, mechanical and corrosion behavior, osseointegration, and esthetic responses of implantable ceramic coatings, especially considering the last published reports, are reviewed in detail. Besides, an answer to the “are the coatings suitable for in vivo conditions?” is investigated.
... As a solution to prevent ions release, a chemically stable and biocompatible coating on NiTi is thought to be effective. Hydroxyapatite is well-known as the most popular biocompatible coating that reduces or eliminates the release of ions (Koumya et al. 2021;Gkomozaa et al. 2019;Chen et al. 2019;Vilardella et al. 2020). Hydroxyapatite coating is applied on the titanium alloys using various techniques including: hydrothermal method, solid-state reaction, coprecipitation, sol-gel, sputtering, mechanochemical, mechanochemical-hydrothermal, microemulsion, and others. ...
The investigated cast Ni50-Ti50 shape memory alloy was prepared using a vacuum arc furnace. The cast samples were subjected to in-vitro biocompatibility studies according to ISO 10993-12:2004, and compared to other samples Ni-Ti orthodontic wires commercially available at the dental market. The cast samples were hydroxyapatite-coated using the electrodeposition technique. The effect of surface treatment on the coating quality was addressed. The hydroxyapatite-coated samples were investigated using electrochemical impedance (EIS) and potentiodynamic techniques. Coated samples were also examined using a scanning electron microscope to inspect the coating morphology. Cytotoxicity tests on MG63 and H9C2 cell lines showed the safety and biocompatibility of the cast NiTi alloy, with a direct relationship between the incubation period of the tested samples and cell viability. Well-adhered hydroxyapatite coating was obtained on the surface-treated NiTi samples using the electrodeposition technique. EDS analysis showed a hydroxyapatite coating having a calcium to phosphorus ratio close to that of the natural bone. Electrochemical tests indicated that the highest corrosion resistance was obtained for the uncoated samples followed by the anodized sample and finally the hydroxyapatite-coated samples due to their high porosity.
... No spherical particles were seen. Gkomoza et al. reported similar structures achieved by plasma spraying of the same HA powder (XPT-D-703), but with a higher degree of melting [38]. Primary grain nanostructures were seen to be partially melted. ...
Air plasma spraying (APS) is a common method of producing hydroxyapatite (HA) coatings for alloprosthetic implants. Modification of HA spraying potentially may diminish the risk of in-flammation and local infection during bone implantation. Titanium implants were HA coated with different deposition process parameters. HA powder was deposited using APS with axial powder injection at three different distances (100, 120, and 140 mm). Surface morphology were examined and direct contact cytotoxicity of HA coatings was evaluated according to norm ISO 10993 5:2009. The response of monocytes to HA was assessed via the activation of transcription nuclear factor. All coatings had a lamellar structure. HA sprayed at a distance of 120 mm showed the highest roughness and little phase change. The analysis of the results of the conducted research showed that plasma-spraying distance during the HA coating process had a negligible impact on their bio-compatibility. The results obtained for a distance of 120 mm showed a slight increase in the bio-logical properties tested. Moreover, HA coatings sprayed with different distances were not cy-totoxic and did not stimulate the NF-kB. Bare titanium was less susceptible to colonization by Staphylococcus aureus than HA coated surfaces. HA constitutes a potentially good, low-cost, non-cytotoxic material for joint prostheses
... Some parameters, such as adhesive strength between substrate and coating, elements of precursors, porosity and composition of the coatings could potentially affect corrosion behavior [24]. Compared to different coating methods, plasma spray was a simple technique and contains a wide deposition rate, widespread particle size range and exhibits high -quality coatings [25,26]. ...
There are several attempts to improve surface characteristics of biomaterials with thick film coatings. In this research, a class of protective coating layers of bi-layered Hydroxyapatite (HA)/Al2O3-SiO2 (with 10, 20, 30 %wt SiO2) were deposited on titanium (Ti) surfaces by plasma spray technique. The surface features of the applied coating layers were evaluated in detail to confirm the effectiveness of the technique for further biomedical applications. The results demonstrated that uniform and bi-layered plasma sprayed coatings can be successfully prepared through the optimization of engineering parameters. Also, it was found that the roughness of the bi-layered coatings increases with increasing the number of coating layers. The corrosion behavior of the coated and uncoated samples was comparatively investigated using electrochemical tests. The current density (icorr) was measured 0.27μA/cm2, 0.28 μA/cm2, 0.23 μA/cm2, 0.79 μA/cm2 for HA, (HA)/Al2O3-SiO2 (with 10, 20, 30 %wt SiO2), respectively. According to the results, corrosion resistance of samples with 20% SiO2 is significantly improved compared to the single-layer HA and bare Ti. The outcomes of FESEM results revealed that porosity and cavities related to evaporation of adhesive PVA and it is confirmed by increasing the percentage of silica to more than 20%, porosity has increased. In conclusion, the proposed coating system showed promising abilities for future biomedical applications. It could be optimized and improved by changing the structural characteristics of the substrate, chemical composition and porosity of the coating layers.
... It can additionally help to determine the morphological changes of coatings at different time intervals in SBF after in vitro drug release tests [108]. In addition to the morphology and microstructure analysis of the coating surface [88,92,109] or cross sections [67, 83,91], the thickness of the coatings and the adhesion of osteoblasts on coated implants can be investigated [67, 110,111]. For example, Eawsakul et al. [110] used SEM to measure the thickness of PLGA/BMP-2 coating on Ti and to study osteoblast adhesion. ...
The development of bioactive coatings for orthopedic implants has been of great interest in recent years in order to achieve both early- and long-term osseointegration. Numerous bioactive materials have been investigated for this purpose, along with loading coatings with therapeutic agents (active compounds) that are released into the surrounding media in a controlled manner after surgery. This review initially focuses on the importance and usefulness of characterization techniques for bioactive coatings, allowing the detailed evaluation of coating properties and further improvements. Various advanced analytical techniques that have been used to characterize the structure, interactions, and morphology of the designed bioactive coatings are comprehensively described by means of time-of-flight secondary ion mass spectrometry (ToF-SIMS), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), 3D tomography, quartz crystal microbalance (QCM), coating adhesion, and contact angle (CA) measurements. Secondly, the design of controlled-release systems, the determination of drug release kinetics, and recent advances in drug release from bioactive coatings are addressed as the evaluation thereof is crucial for improving the synthesis parameters in designing optimal bioactive coatings.
... [20][21][22][23] Researchers have investigated adhesion strength, microhardness, bacterial adhesion and bioactivity of the HAp coatings prepared by varying processing parameters and powder particle size. [20][21][22][23][24][25][26][27][28] They have observed that thermal spray HAp coatings, especially plasma spray, generates phases such as amorphous calcium phosphate (ACP), Tri-calcium phosphate (TCP) and tetra-calcium phosphates (TTCP). [15][16][17] These phases contribute to enhancing the coating healing action. ...
Artificial material such as stainless steel (SS) is widely used for orthopaedic applications owing to its superior properties, ease of fabrication and lower cost. However, in the body environment, stainless steel can leach toxic elements such as nickel and chromium. To prevent this, a hydroxyapatite (HAp) coating having chemical characteristics very similar to the human bone was deposited on a medical-grade UNS S31254 austenitic stainless steel by a Low-velocity oxy-fuel spray gun (LVOF). The coating was characterised by using a field emission scanning electron microscope (FESEM), X-ray diffractometer (XRD) and Fourier transform infrared spectroscope (FTIR). The adhesion strength, microhardness and corrosion behaviour were studied using the Tensometre, Vickers microhardness tester and potentiodynamic polarisation with electrochemical impedance spectroscope. The bacterial adhesion and bioactivity of the coating were also evaluated. The LVOF sprayed HAp coating has shown better corrosion resistance, higher bioactivity and higher hardness than the uncoated steel. The presence of tricalcium phosphate, octa-calcium phosphate (OCP) and tetra-calcium phosphate (TTCP) was found in the coating. LVOF sprayed HAp coating is also found suitable in lowering the bacterial adhesion on the steel substrate.
... These coatings promote the growth of bone cells and advance the contact among body tissue and coated substrates ( Ref 17,18). Different methods were used to deposit coatings on the substrates, such as sol-gel coatings, RF magnetron sputtering, electrochemical depositions, and thermal spray, respectively (Ref [19][20][21]. Among all these coating methods, plasma spraying is a simple process that has a superior deposition efficiency, including a broad variety of particle sizes. ...
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.
... Various methods have been developed for HAp coatings including thermal spraying [plasma spraying (Levingstone et al., 2015;Heimann, 2016;Xu et al., 2016;Harun et al., 2018;Gkomoza et al., 2019), flame spraying Mardali et al., 2019), high velocity oxy-fuel spraying (Bolelli et al., 2007a(Bolelli et al., , 2007bMardali et al., 2019), detonation gun spraying (Gledhill et al., 1999(Gledhill et al., , 2001Sapra et al., 2008) and so on], sputter deposition (Mediaswanti et al., 2014;Vladescu et al., 2016;Ozeki et al., 2017;Surmenev et al., 2017;Qadir et al., 2019), pulsed laser deposition (Koch et al., 2007;Pereiro et al., 2012;Duta et al., 2013;Rajesh et al., 2013;Popescu-Pelin et al., 2017;Hidalgo-Robatto et al., 2018;Rau et al., 2018), ion-beam assisted deposition (Choi et al., 2000;Hamdi and Ide-Ektessabi, 2003;Cotrut et al., 2018) dip coating (Khalid et al., 2013;Javadi et al., 2019), sol-gel coating (Asri et al., 2016;Javadi et al., 2019), electrophoretic deposition (Manoj Kumar et al., 2016;Farrokhi-Rad, 2017, 2018Farrokhi-Rad et al., 2017;Göncü et al., 2017;Baştan et al., 2018;Patel et al., 2019;Pawlik et al., 2019) and hot isostatic pressing (Onoki and Hashida, 2006;Harun et al., 2018). Among them, atmospheric plasma spraying (APS) has been the most frequently used and commercially accepted method of HAp coatings on orthopaedic implants (Surmenev, 2012;Levingstone et al., 2015;Heimann, 2016Heimann, , 2017. ...
Polyetheretherketone (PEEK) is a biocompatible polymer with good mechanical strength, thermal and chemical stability and is suitable for magnetic resonance and X-ray imaging. Moreover, density and elasticity of PEEK is closer to bones compared to metals. Nevertheless, the hydrophobicity of the PEEK surface causes a soft tissue formation at the bone/implant interface that prevents direct bone apposition. Although numerous methods have been developed for improving PEEK's bioactivity, the most widely used and accepted method have been coating the surface with a thin layer of osseointegrative material by thermal spraying. Most widely used coating materials in the manufacture of orthopaedic implants have been hydroxyapatite (HAp) and titanium. Thus, this review focuses on the recent progress on HAp and Ti coatings deposited by plasma spraying methods on PEEK implants.
... Various methods have been developed for HAp coatings including thermal spraying [plasma spraying (Levingstone et al., 2015;Heimann, 2016;Xu et al., 2016;Harun et al., 2018;Gkomoza et al., 2019), flame spraying Mardali et al., 2019), high velocity oxy-fuel spraying (Bolelli et al., 2007a(Bolelli et al., , 2007bMardali et al., 2019), detonation gun spraying (Gledhill et al., 1999(Gledhill et al., , 2001Sapra et al., 2008) and so on], sputter deposition (Mediaswanti et al., 2014;Vladescu et al., 2016;Ozeki et al., 2017;Surmenev et al., 2017;Qadir et al., 2019), pulsed laser deposition (Koch et al., 2007;Pereiro et al., 2012;Duta et al., 2013;Rajesh et al., 2013;Popescu-Pelin et al., 2017;Hidalgo-Robatto et al., 2018;Rau et al., 2018), ion-beam assisted deposition (Choi et al., 2000;Hamdi and Ide-Ektessabi, 2003;Cotrut et al., 2018) dip coating (Khalid et al., 2013;Javadi et al., 2019), sol-gel coating (Asri et al., 2016;Javadi et al., 2019), electrophoretic deposition (Manoj Kumar et al., 2016;Farrokhi-Rad, 2017, 2018Farrokhi-Rad et al., 2017;Göncü et al., 2017;Baştan et al., 2018;Patel et al., 2019;Pawlik et al., 2019) and hot isostatic pressing (Onoki and Hashida, 2006;Harun et al., 2018). Among them, atmospheric plasma spraying (APS) has been the most frequently used and commercially accepted method of HAp coatings on orthopaedic implants (Surmenev, 2012;Levingstone et al., 2015;Heimann, 2016Heimann, , 2017. ...
Polyetheretherketone (PEEK) is a biocompatible polymer with good mechanical strength, thermal and chemical stability and is suitable for magnetic resonance and X-ray imaging. Moreover, density and elasticity of PEEK is closer to bones compared to metals. Nevertheless, the hydrophobicity of the PEEK surface causes a soft tissue formation at the bone/implant interface that prevents direct bone apposition. Although numerous methods have been developed for improving PEEK’s bioactivity, the most widely used and accepted method have been coating the surface with a thin layer of osseointegrative material by thermal spraying. Most widely used coating materials in the manufacture of orthopaedic implants have been hydroxyapatite (HAp) and titanium. Thus, this review focuses on the recent progress on HAp and Ti coatings deposited by plasma spraying methods on PEEK implants.
... Different surface modification techniques i.e. GTAW cladding [7,8], physical vapor deposition (PVD) [9,10], thermal spraying [11,12], electroplating [13,14], lithography [15,16], etc. have been actively used to modify the surface properties like corrosion resistance, hardness and wear properties of titanium alloy. However, most of these techniques require complex apparatus and cannot be used for localized coating process [17]. ...
In the present study, hard, wear, and corrosion resistance coating is deposited on titanium alloy with hexagonal boron nitride powder (avg. size 70 nm) suspended in deionized water by micro-electro discharge coating process. The influence of input process parameters on surface integrity, wear properties, and corrosion resistance is studied. XRD analysis of coating surface shows the presence of phases such as BN, Al2O3, TiN, TiAlN, TiO, and CuO. Micro-hardness of the coating surface increases by five times as compared to titanium alloy (parent material). At the parameter settings of 60 V, 0.7 duty factor, and 12 g/l, the maximum deposition rate of 5.65 ± 0.1 × 10−4 g/min and recast layer thickness of 13.1 μm is obtained. Pin on disk wear test results reveal the reduction of wear rate of the coated surface to one-fourth of that of the base material. The average coefficient of friction (COF) for the deposited BN surfaces reduces to 0.26 from 0.4 (substrate material). Corrosion resistance of the coated surface is found to be 1.24 μm/year in flowing water conditions and 1.07 μm/year in stagnant water whereas for the parent material it is 5.92 μm/year in flowing water condition and 4.89 μm/year for stagnant water condition.
The use of biogenic waste for multipurpose materials has started to be encouraged in the current decade to support the world’s environmental sustainability campaign. Biogenic calcium phosphate-derived materials are potential biomaterials because of their similar properties to human bone. This paper used hydroxyapatite (HAp) powder derived from green mussel shells (Perna viridis) to coat the AISI 316L metallic implant material using the electrophoretic deposition coating method. In this study, the post-deposition withdrawal speeds of 5mm/s, 3mm/s, and 1mm/s were varied to find their effect on the quality of the HAp coating layer. Crystallography, micrography, and image processing were used to characterize the coating and calculate the percentage of HAp layer and cracks. The crystallographic data shows the HAp peaks, which conclude that the green mussel shells HAp successfully coat the substrate and can be used to coat the AISI 316L implant material. However, the appearance of the substrate crystal peaks and color difference on high withdrawal speed specimens conclude that the coating layer has cracks. In conclusion, the emergence of cracks can be minimized using 1mm/s post-deposition withdrawal speed and eventually produce high-quality HAp coating.
The delayed tissue–implant interactions in metallic implants coated with hydroxyapatite (HA) paved the way for the development of alternative bioactive coatings. In this study, bi-layered functional gradient (HA-CS) coating was formulated by the atmospheric plasma spray (APS) process on Ti6Al4V alloy. The HA layer was applied at the metal interface to ensure long-term stability, while the calcium silicate (CS) outer layer was applied to achieve fast tissue–implant interactions. Moreover, single-layered HA and CS coating were also formulated for comparative analysis. The phase compositions, coating microstructure, chemical properties, microhardness, porosity, surface roughness, and in-vitro bioactivity were investigated. The CS top layer showed high porosity and surface roughness with respect to the inner HA layer, which constitutes an optimum microstructure to promote bioactivity. The microhardness of the outer CS layer of HA-CS was 520.3 ± 80.8 HV, while the corresponding value for the inner HA layer was 291.7 ± 45.7 HV. HA-CS and CS coatings demonstrated higher in-vitro bioactivity compared to HA coating. On the contrary, HA coating (3.76 mpy) displayed better corrosion resistance than the HA-CS (4.17 mpy) and CS coatings (4.34 mpy). The in-vitro results indicated that the HA-CS coating could promote the healthy development of osteoblast-like MG-63.
Metallic implants have the disadvantage of being insufficiently biologically active despite their good mechanical properties and general affordability. Therefore, their bone growth at the implant site in an osteoinductive and osteoconductive manner could be improved by using bioactive coatings with incorporated active ingredients (antibiotics, anti-inflammatory drugs, growth factors, osteoclast inhibitors, anticoagulants, etc.) that are released locally at the implant site in a controlled manner. In addition, the long-term exposure of metallic implant materials to a corrosive environment (human body fluids) can lead to toxic corrosion-induced ion release. To ensure the biological, non-corrosive, and appropriate mechanical properties of the implant-coating system, the choice of the coating method is crucial. This review describes recent developments in the application of bioactive coatings on metal implant materials, such as 3D printing, electrospinning, electrophoretic deposition, dip coating, drop casting, sol-gel deposition, biomimetic deposition, plasma spraying, layer-by-layer deposition, physical vapour deposition, and the formation of titanium oxide nanotubes by anodization. In addition, this work addresses promising ways to incorporate active ingredients into coatings through various entrapment methods of nano- and micro-encapsulation to achieve the desired controlled release.
In this study, conventional and nanostructured Al2O3 and Al2O3-Y2O3 coatings were produced by atmospheric plasma spraying. Phase composition, microstructure and chemical composition studies were performed on the coatings. Microhardness, crack propagation resistance and bonding strength of the coatings were evaluated. Wear testing was also carried out by a pin-on-disc machine at loads of 2, 10 and 20 N. The results showed that the coatings obtained from nano-agglomerated powders had a Bi-modal microstructure. The addition of Y2O3 resulted in stabilizing desired α-Al2O3 phase. Nanostructured coatings displayed more increase in I α/Iγ than conventional types. Composite coatings showed higher bonding strength than individual Al2O3 coatings, due to the better adhesion of the splats, chemical bonding of Y2O3 and Al2O3, and the better melting and wetting of Y2O3 in the composite coatings. Nanostructured alumina coating had about twice crack propagation resistance more than conventional type. Despite the lower crack propagation resistance, conventional coatings showed higher wear resistance than nanostructured coatings due to their higher adhesion strength and hardness and denser microstructure.
Deep transfer learning can make full use of pre-trained neural networks and has been used in many cases with limited sample data. In this work, parameter-transfer learning was implemented to model the relationship between process control parameters and in-flight particle behavior. Six different parameter-transfer learning models were designed to fine-tune the variables of the convolutional neural network (CNN) model pre-trained with a dataset of yttria-stabilized zirconia (YSZ) particles. Then transfer learning models were trained with the new dataset obtained from simulation results of NiCrAlY particles and the losses of different models in the training set and test set were compared. Results indicate that the method in which the entire pre-trained CNN model was fine-tuned, combined with a decreasing learning rate, exhibited the lowest loss in the training dataset and the highest testing accuracy. Particle status distributions obtained from the control parameters predicted by the transfer learning model were found to be in good agreement with the corresponding designed target values.
Biomineralization approaches have been increasingly adopted to synthesizing advanced materials with superior properties. Nevertheless, the potential influence of inorganic trace elements on the mineralization process of collagen has been rarely reported, despite of the significant progress achieved on exploiting the critical roles of organic polymers in regulating the collagen mineralization. To this aim, the potential roles of Si, Zn and Sr in regulating the mineralization of gelatin-hydroxyapatite (HA) composite fibers have been examined in this study. The results indicated that the incorporation of trace elements not only promoted the biomineralization of gelatin, but also led to drastic change in the mineralization behavior. In particular, the gelatin-SiHA sample showed uniform mineralization predominantly inside the fibers, with nucleation and growth directions along the c-axis of the gelatin fibers. On the contrary, the gelatin-HA sample showed nucleation outside the fibers and spherical mineral crystals on top of fibers, typical structure for heterogeneous nucleation. As the mineralization process proceeded, the gelatin-ZnHA and gelatin-SrHA samples evolved into having similar structure as the gelatin-SiHA sample, despite of showing totally different mineralization behaviors at early time. Overall, the incorporation of trace elements seemed to lower the nucleation barriers, led to a more homogeneous mineralization mode within the fiber region and formation of mineralized structures closer to those in natural bone. Moreover, mineralized samples with trace elements demonstrated improved adhesion and cytoskeleton organization of osteoblastic cells. Such finding would provide important insight for understanding the mineralization process and the optimal design of advanced biological materials.
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.
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 Zinc Oxide (ZnO) 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 ZnO 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/ZnO reinforced coatings are a promising approach to improve surface properties and corrosion behavior of Mg alloys for future bone implant applications.
Ionic substituted calcium phosphates have received much attention for their use as implant materials because of their ability to mimic natural hard tissues. In this work, the properties of hydroxyapatite ceramic doped with small amounts of zinc ions (5, 10, and 15 mol%) by using a wet chemical precipitation route were studied. XRD spectra revealed that adding zinc led to the development of a biphasic mixture composed of hydroxyapatite (HA) and β-TCP phases, which affected the morphology, crystallinity, and crystallite size of the precipitates. With increasing zinc ion substitution in the HA lattices, the degree of crystallinity of the powders reduces due to the additional formation of β-TCP phase. Slender, elongated, and highly agglomerated particles were observed for all synthesized powders. However, calcination at 700 °C caused the particles to become more spherical, having diameters ranging from 30 to 37 nm. An increase in the concentration of zinc ions promoted the β-TCP phase, which ultimately altered the lattice parameters of the HA structure and suppressed the growth of particles.
New hydroxyapatite (HAp) ceramics substituted with 10, 30 and 50 at.% of bismuth were synthesized by conventional solid state reaction at high temperature T = 1300 °C, and characterized via X-ray diffraction, scanning electron microscopy, Fourier transform infrared and Raman spectroscopies; dielectric properties were also investigated. The hydroxyl groups observed in infrared spectra confirmed the HAp phase in the studied samples. The crystallite size was estimated by Scherrer's formula and the Williamson–Hall plot, while lattice parameters and the unit cell volume of the samples were measured according to Bi content.Scanning electron microscope images revealed the presence of grains with irregular sizes developed within larger aggregations. Measured relative dielectric permittivity and dielectric loss are slightly affected by Bi content, while the alternating current conductivity increases with a rise frequency, and decreases at increasing of Bi content. The HApBi50% sample presents the optimal dielectric properties.
Objectives. To analyse the chemistry and bioactivity of NeoMTA Plus in comparison with the conventional root repair materials. Method and Materials. Unhydrated and hydrated (initial and final sets) materials were analysed by Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD). For bioactivity study, small holes of dentin discs were filled with either materials, immersed in PBS for 15 days, and analysed with FTIR and scanning electron microscope with energy dispersive X-ray (SEM/EDX). The calculation of crystallinity and carbonate/phosphate (CO 3 /PO 4) ratio of surface precipitates (from FTIR) and calcium/phosphate (Ca/P) ratio (from EDX) was statistically analysed using t-test or ANOVA, respectively, at 0.05 significance. Results. Both materials are tricalcium silicate-based that finally react to be calcium silicate hydrate. NeoMTA Plus has relatively high aluminium and sulfur content, with tantalum oxide as an opacifier instead of zirconium oxide in MTA Angelus. NeoMTA Plus showed better apatite formation, higher crystallinity and Ca/P but lower CO 3 /PO 4 ratio than MTA Angelus. SEM showed globular structure with a small particle size in NeoMTA Plus while spherical structure with large particle size in MTA Angelus. Conclusion. Due to fast setting, higher crystallinity, and better bioactivity of NeoMTA Plus, it can be used as a pulp and root repair material.
The possibility of producing nano-sized coatings by thermal spray processes seems to be very interesting for many industrial applications. Due to the small size of the grains, it is possible to achieve the properties which are not observed in the micrometric scale on the same kind of material. The aim of the current work is to present the alternative methods for conventional powder plasma spraying (APS) which is well known technology for deposition of micron-sized coatings using powder feedstock. Two plasma spraying processes with liquid feedstock were used suspension plasma spraying (SPS) and solution precursor plasma spraying (SPPS) using aqueous solution directly from wet chemical pre- cipitation process. All experiments were performed based on hydroxyapatite, which is a very important material for biomedical applications. Coatings were produced by three mentioned methods but the deposition process was realized using only one spray set-up equipped with SG-100 plasma torch. Short background of the three different processes performed followed by a short description of liquid feedstock preparation is presented. Microstructure investigation and phase composition analysis of the prepared coatings were carefully characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD) respectively. Finally, the analysis and comparison of coatings deposited by different plasma spray processes were discussed. Natryskiwanie plazmowe powłok hydroksyapatytu z wykorzystaniem proszku, zawiesiny oraz roztworu AbstraktMożliwość wytwarzania powłok o budowie nanometrycznej wydaje się być bardzo interesująca pod kątem ich zastosowania w wielu gałęziach przemysłu. Dzięki bardzo drobnoziarnistej strukturze możliwe jest osią- gnięcie właściwości powłok, które nie są możliwe do zaobserwowania w tych samych materiałach lecz w skali mikro. Celem niniejszej pracy jest przedstawienie alternatywnych metod dla konwencjonalnego natryskiwania plazmowego (APS), które jest dobrze poznanym procesem wytwarzania powłok charakteryzująch się budową mikrometryczną. Zaprezentowano dwa nowe procesy natryskiwania plazmowego z fazy ciekłej natryskiwanie plazmowe zawieisn (SPS) oraz natryskiwanie plazmowe roztworów (SPPS). Wszystkie eksperymenty przeprowadzono z wykorzystaniem hydroksyapatytu, który jest bardzo istotnym materiałem dla zastosowań biomedycznych. Powłoki zostały wytworzone z użyciem trzech wymienionych technologii, jednak proces natryskiwania realizowany był za pomocą jednego stanowiska wyposażonego w palnik plazmowy SG-100. W pracy przedstawiono zarys teoretyczny wykorzystanych metod natryskiwania wraz z opisem procedury przygotowania materiału wejściowego (proszku, zawiesiny oraz roztworu). Następnie przedstawiono badania mikrostruktury i analizę składu fazowego przygotowanych powłok, które zostały wykonane z wykorzystaniem skaningowej mikroskopii elektronowej (SEM) i dyfrakcji promieni rentgenowskich (XRD). Przeprowadzono również analizę i porównanie powłok wykonanych z użyciem różnych procesów natryskiwania plazmowego.
The possibility of producing nano-sized coatings by thermal spray processes seems to be very interesting for many industrial applications. Due to the small size of the grains, it is possible to achieve the properties which are not observed in the micrometric scale on the same kind of material. The aim of the current work is to present the alternative methods for conventional powder plasma spraying (APS) which is well known technology for deposition of micron-sized coatings using powder feedstock. Two plasma spraying processes with liquid feedstock were used – suspension plasma spraying (SPS) and solution precursor plasma spraying (SPPS) using aqueous solution directly from wet chemical precipitation process. All experiments were performed based on hydroxyapatite, which is a very important material for biomedical applications. Coatings were produced by three mentioned methods but the deposition process was realized using only one spray setup equipped with SG-100 plasma torch. Short background of the three different processes performed followed by a short description of liquid feedstock preparation is presented. Microstructure investigation and phase composition analysis of the prepared coatings were carefully characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD) respectively. Finally, the analysis and comparison of coatings deposited by different plasma spray processes were discussed.
In order to increase the bone bioactivity of metallic implants, hydroxyapatite (HA: Ca 10 (PO 4) 2 (OH) 6) is often coated on their surface so that real bond with surrounding bone tissue can be formed. In present study, HA coatings were deposited on AISI 316L SS and titanium using shrouded plasma spray process. The coated specimens were subjected to X-ray diffraction (XRD) analysis, field emission scanning electron microscopy (FE-SEM/EDAX). The polarization studies in simulated body fluid (SBF) were conducted to evaluate the corrosion resistance of bare and coated specimens. It was found that the hydroxyapatite coating provided excellent corrosion resistance. The resistance to corrosion was found independent on substrates
Joint replacement is a major orthopaedic procedure used to treat joint osteoarthritis. Aseptic loosening and infection are the two most significant causes of prosthetic implant failure. The ideal implant should be able to promote osteointegration, deter bacterial adhesion and minimize prosthetic infection. Recent developments in material science and cell biology have seen the development of new orthopaedic implant coatings to address these issues. Coatings consisting of bioceramics, extracellular matrix proteins, biological peptides or growth factors impart bioactivity and biocompatibility to the metallic surface of conventional orthopaedic prosthesis that promote bone ingrowth and differentiation of stem cells into osteoblasts leading to enhanced osteointegration of the implant. Furthermore, coatings such as silver, nitric oxide, antibiotics, antiseptics and antimicrobial peptides with anti-microbial properties have also been developed, which show promise in reducing bacterial adhesion and prosthetic infections. This review summarizes some of the recent developments in coatings for orthopaedic implants.
In this paper we present a synthesis method for obtaining hydroxyapatite nanopowders by chemical precipitation. As the starting reagents, analytical grade Ca(OH)2, H3PO4 and NH4OH were used. The proposed method led to obtaining a hydroxyapatite with a high degree of crystallinity and purity. The synthesized samples were characterized by X-ray diffraction (XRD), Fourier transformed-infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) techniques.
Hydro xyapatite (HAP) is a biocompatib le ceramic that is widely used in a number of bio medical applications and devices. Due the close similarity between nanometer scale fo rms of HAP and the mineral phase found in the natural bone matrix, recent studies have focused on understanding the structure of HAP for its inclusion in a new generation of novel composites. In this study two commercially available software packages Materials Studio and Endeavour ® 1.7b were used to model the crystal structure of a nanometre scale HAP powder fro m X-ray powder diffraction data. The nanometre scale HAP used in this study was prepared via a wet precipitation technique under the influence of ultrasonic irrad iation. The ma in reactants in this process were[Ca(NO 3) 2 ] and[KH 2 PO 4 ], while[NH 4 OH] was used as the precipitator. During the process the calciu m phosphate ratio was set at 1.67 and the pH was maintained at 9. The resultant slurries were then thermally t reated in rad iant tube furnace to produce nanometre scale particles with a mean diameter o f 30 n m.
This paper reports on the response of hydroxyapatite (HA) coatings, fabricated using two deposition technologies, to immersion in simulated body fluid (SBF). The deposition methods used were: plasma spray, a commercial standard, and CoBlast, a novel low temperature microblast technique. In the case of the latter, HA coatings are deposited by simultaneous blasting HA and abrasive powders concentrically at a metallic substrate, resulting in a thin layer of HA (approx. 2.5 µm thick). Groups of the CoBlast and plasma spray HA coatings were immersed in 7 ml of SBF solution for 1, 2, 4, 7, 14 and 28 days, and were subsequently removed and examined for any alterations caused by the SBF solution. It was noted from this study that the CoBlast HA coatings appeared to undergo a two step calcium phosphate recrystallisation process; initial homogenous nucleation and subsequent heterogeneous nucleation. Conversely recrystallisation on the plasma spray coatings appeared to proceed largely through a heterogeneous nucleation process. Two factors that may influence the differences in HA recrystallisation is the presence of amorphous HA resulting in rapid dissolution, and/or the significantly lower surface area (roughness) offered to the SBF solution by the CoBlast coatings. The interpretation of recrystallisation mechanisms from this preliminary study is limited however by the differences in coating morphology and thickness (27 versus 2 µm) for the plasma spray and CoBlast HA coatings respectively.
Hydro xyapatite (HAP) is a biocompatib le ceramic that is widely used in a number of bio medical applications and devices. Due the close similarity between nanometer scale fo rms of HAP and the mineral phase found in the natural bone matrix, recent studies have focused on understanding the structure of HAP for its inclusion in a new generation of novel composites. In this study two commercially available software packages Materials Studio and Endeavour ® 1.7b were used to model the crystal structure of a nanometre scale HAP powder fro m X-ray powder diffraction data. The nanometre scale HAP used in this study was prepared via a wet precipitation technique under the influence of ultrasonic irrad iation. The ma in reactants in this process were[Ca(NO 3) 2 ] and[KH 2 PO 4 ], while[NH 4 OH] was used as the precipitator. During the process the calciu m phosphate ratio was set at 1.67 and the pH was maintained at 9. The resultant slurries were then thermally t reated in rad iant tube furnace to produce nanometre scale particles with a mean diameter o f 30 n m.
Hydroxyapatite (HAP) nanoparticles, typically 20 ± 5, 40 ± 10 and 80 ± 12 nm in diameter, were prepared and their effects on the proliferation of two bone-related cells, bone marrow mesenchymal stem cells (MSCs) and osteosarcoma cells (U2OS) were studied. The cell culture experiments showed improved cytophilicity of the nanophase mineral as compared with conventional HAP. Greater cell viability and proliferation of MSCs were measured on the nano HAP, remarkably for 20 nm sized particles. Interestingly, the growth of osteosarcoma cells was inhibited by the nano HAP and 20 nm sized particles were the best retardant. It is suggested that the HAP nanoparticles can exhibit favorable cell proliferation to optimize biological functionality, in which the particle size is believed to play a key role. These in vitro findings are of great significance for the understanding of cytophilicity and biological activity of nanoparticles during biomineralization.
The nano Hydroxyapatite (HA) powder was derived from a novel peroxide-based route (PBR) using calcium nitrate, phosphoric acid and hydrogen peroxide as peroxo-precursor. In present work, the effect of nano HA powder on the microstructure and properties of thermally sprayed HA coatings was investigated. The obtained powders were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD pattern of hydroxyapatite powder corresponded to that of hydroxyapatite and tricalcium phosphate. The nano HA powder was then deposited onto stainless steel substrates using High Velocity Oxy-Fuel (HVOF) method. The infuence of the crystallization was evaluated by XRD and SEM. Mechanical property in terms of hardness and bioactivity of the coatings were investigated by Vickers micro hardness testing and soaking in simulated body fluid (SBF), respectively. The results showed that the HA coatings were a mixture of amorphous and crystalline phase. The hardness value of 2.15 ± 0.08 GPa was obtained for the synthesized HA powder coating (SHAC). After soaking in SBF for 14 days, the layer formation of apatite could be observed.
Advanced bioceramics have played integral roles in treatment modalities for damaged or diseased human joints and osseous defects. This paper reviews the uses and properties of ceramics and ceramic coatings variously employed as articulation devices in hip, knee, shoulder, and other joints, either as self-mated surfaces, or against polyethylene (both conventional and highly cross-linked versions), or for osseous- fixation as arthrodesis devices, bone scaffolds, and substitutes in the spine or extremities. The modern uses of oxide and non-oxide materials in these applications will be discussed, followed by an assessment and comparison of their mechanical and physicochemical properties. Recent developments in new bioceramic materials and composites along with advanced processing and testing methods are presented. Advanced bioceramics and coatings are expected to have increasing use in orthopaedics because of their unique combination and range of properties including strength and toughness, hardness and wear resistance, biocompatibility, bacteriostasis, and osseointegration.
A bioactive glass topcoatwas introduced to modify the surface morphology and in-vitro reactivity of hydroxyapatite
(HA) coatings for biomedical applications. With this aim, a CaO-rich bioactive glass, termed BG_Ca (wt.%: 4.7
Na2O, 42.3 CaO, 6.1 P2O5, and 46.9 SiO2),was selected due to its good bioactivity and lowtendency to crystallize at high temperature. The standardHA coatings were sprayed through atmospheric plasmaspray (APS) on steel substrates starting from commercial powders (“APS-HA” samples). The HA coatings, in turn, were subsequently coated with a thin layer of bioactive glass by suspension plasma spray (SPS), thus obtaining the duplex systems (“APS-HA/SPS-BG_Ca” samples). The samples with andwithout the BG_Ca layer were analysed by microstructural characterization and by in vitro tests in simulated body fluid (SBF). The analysis revealed an increased reactivity of the APS-HA/SPS-BG_Ca samples compared to the glass-free APS-HA coatings.
A study was conducted to develop and study the possibility of using magnesium as a degradable bio-compatible implants. A magnesium ingot was cut into 1-2 cm3 coupons which was used for corrosion tests and making electrodes. The Hank solution was used as a simulated body fluid (SBF) and its pH was adjusted with HCl to a slightly acidic level (pH~ 6) to avoid precipitation or formation of sediments in the solution. The coupons were polished with up to 1000 grit SiC paper and AC impedance spectra and polarization curves were analyzed. It was observed that magnesium is compatible with the human body and the direct corrosion product Mg2+ can be tolerated in the human body, while rapid accumulation of corrosion by-products such as hydrogen gas and hydroxides may exclude the possible application of magnesium vent in vascular system. Result shows that magnesium vents cannot be used vascular system due to hydrogen gas, but it can be used as implant for broken bones.
Thermal spray coatings produced from nanostructured ceramic agglomerated powders were tailored for different applications,
some of which required almost completely opposite performance characteristics (e.g., anti-wear and abradable coatings). The
influence of nanostructured materials on important areas, such as, thermal barrier coatings (TBCs) and biomedical coatings
was also investigated. It was determined that by controlling the distribution and character of the semi-molten nanostructured
agglomerated particles (i.e., nanozones) embedded in the coating microstructure, it was possible to engineer coatings that
exhibited high toughness for anti-wear applications or highly friable for use as abradables, exhibiting abradability levels
equivalent to those of metallic-based abradables. It is shown that nanozones, in addition to being very important for the
mechanical behavior, may also play a key role in enhancing and controlling the bioactivity levels of biomedical coatings via
biomimetism. This research demonstrates that these nanostructured coatings can be engineered to exhibit different properties
and microstructures by spraying nanostructured ceramic agglomerated powders via air plasma spray (APS) or high velocity oxy-fuel
(HVOF). Finally, in order to present readers with a broader view of the current achievements and future prospects in this
area of research, a general overview is presented based on the main papers published on this subject in the scientific literature.
Select functions of osteoblasts (bone-forming cells) on nanophase (materials with grain sizes less than 100 nm) alumina, titania, and hydroxyapatite (HA) were investigated using in vitro cellular models. Compared to conventional ceramics, surface occupancy of osteoblast colonies was significantly less on all nanophase ceramics tested in the present study after 4 and 6 days of culture. Osteoblast proliferation was significantly greater on nanophase alumina, titania, and HA than on conventional formulations of the same ceramic after 3 and 5 days. More importantly, compared to conventional ceramics, synthesis of alkaline phosphatase and deposition of calcium-containing mineral was significantly greater by osteoblasts cultured on nanophase than on conventional ceramics after 21 and 28 days. The results of the present study provided the first evidence of enhanced long-term (on the order of days to weeks) functions of osteoblasts cultured on nanophase ceramics; in this manner, nanophase ceramics clearly represent a unique and promising class of orthopaedic/dental implant formulations with improved osseointegrative properties.
The properties and performance of plasma sprayed hydroxyapatite (Ca10(PO4)6(OH)2, i.e. HA) coatings are closely related to their manufacturing process. The objective of the current study is to investigate the phase, structure and microstructure of the coatings and their formation mechanism due to different processing parameters. Hydroxyapatite powders were atmospherically plasma sprayed (APS) using various process parameters. The phase, structure and microstructure of the coatings were investigated and their microhardness measured. Both crystallinity and hydroxyl contents decreased with increasing spray power and stand-off distance (SOD), and increased from the coating interface to the surface. Crystallinity alone cannot reflect coating quality due to the existence of various forms of HA, i.e. unmelted, recrystallized and dehydroxylated, as well as the gradient structures consisting of these forms. Coating microstructure varied from a porous structure to a smooth glassy structure or a typical lamellar structure, and some newly formed nanocrystalline regions were revealed. These effects were associated with the temperature–time experiences of particles, their cooling rates and the heat and hydroxyl accumulation during coating buildup. The coating with highest recrystallization displayed the highest microhardness.
Bone replacement using synthetic and degradable materials is desirable in various clinical conditions. Most applied commercial materials are based on hydroxyapatite, which is not chemically degradable under physiological conditions. Here we report the effect of a long-term intramuscular implantation regime on the dissolution of various low temperature calcium and magnesium phosphate ceramics in vivo. The specimens were analysed by consecutive radiographs, micro-computed tomography scans, compressive strength testing, scanning electron microscopy and X-ray diffractometry. After 15months in vivo, the investigated materials brushite (CaHPO(4)·2H(2)O), newberyite (MgHPO(4)·3H(2)O), struvite (MgNH(4)PO(4)·6H(2)O) and hydroxyapatite (Ca(9)(PO(4))(5)HPO(4)OH) showed significant differences regarding changes of their characteristics. Struvite presented the highest loss of mechanical performance (95%), followed by newberyite (67%) and brushite (41%). This was accompanied by both a distinct extent of cement dissolution as well as changes of the phase composition of the retrieved cement implants. While the secondary phosphate phases (brushite, newberyite, struvite) completely dissolved, re-precipitates of whitlockite and octacalcium phosphate were formed in either particulate or whisker-like morphology. Furthermore, for the first time the possibility of a macropore-free volume degradation mechanism of bioceramics was demonstrated.
Our objective in this study was to determine whether a threshold in sensitivity of human mesenchymal stem cells (hMSC) to isotropic roughness exists. Using electrical discharge machining a very wide range of roughnesses (1.2μm<R(a)<21μm) with a perfectly isotropic, fractal and self-affine topography can be produced on titanium, with a range of roughness overlapping the hMSC length dimensions. The curve of the number of adherent hMSC after 2days culture as a function of roughness showed a U-shape with a minimum number of attached cells for a roughness amplitude R(a)=4.5μm and a distance between surface features (width of peaks and valleys) S(m)=110μm. The maximum cell number was observed at the lowest and highest roughnesses. Due to this very wide range of roughness it was possible to demonstrate that the response of hMSC to roughness varies with the dimensions of the surface features relative to the cell size. Above or below their own size hMSC essentially adhere to the nano and submicron features. When the surface displays features about the same size as hMSC the curvature of these surface features will decrease the number of attached cells by a factor of two. A modelling approach is proposed to help the interpretation of these results. It is hypothesized that this minimal adhesion is a consequence of an unfavourable stress imposed on the cell cytoskeleton.
Bones from different portions of human skeleton are polished and cut to suitable sizes and then subjected to micro-indentation at various loads using Vicker's diamond pyramidal indenter. The Vicker's hardness number is found to differ slightly from portion to portion of the skeleton. Interferometric studies of the indentation reveal that the applied stress of indentation causes a 'pile-up' of material near the corners of the pyramidal indents.
Through the example of two HA ceramics prepared from two HA powders (HAD and HAL), we explored the relation between the physico-chemical qualities of the initial HA powder and the final HA ceramic and their influence on the protein adsorption and cell response to the final HA ceramics. The powders were characterized by XRD, FT-IR, zeta potential, and specific surface area (SSA). Their protein adsorption potential was tested after immersion in culture medium +15% of fetal calf serum. These results were correlated with the protein adsorption potential of the two ceramics (cHAD and cHAL) prepared from the HAD and HAL powders respectively and to the cell attachment after 4, 24 and 72 h on the ceramics. From our results, it appears that a relation can be established between the physico-chemical characteristics of the initial HA powders and the final biological response to the sintered ceramics prepared from these powders. An inverse relation exists between the SSA and the protein adsorption capacity of HA powders and the protein adsorption and cell attachment on HA ceramics. This inverse relation is related to phenomenon occurring during the sintering phase and the formation of inter-granular micro-porosity.
The bone-bonding ability of a material is often evaluated by examining the ability of apatite to form on its surface in a simulated body fluid (SBF) with ion concentrations nearly equal to those of human blood plasma. However, the validity of this method for evaluating bone-bonding ability has not been assessed systematically. Here, the history of SBF, correlation of the ability of apatite to form on various materials in SBF with their in vivo bone bioactivities, and some examples of the development of novel bioactive materials based on apatite formation in SBF are reviewed. It was concluded that examination of apatite formation on a material in SBF is useful for predicting the in vivo bone bioactivity of a material, and the number of animals used in and the duration of animal experiments can be reduced remarkably by using this method.
The Laser Engineered Net Shaping (LENS) method was used to fabricate porous Ti implants. Porous Ti structures with controlled porosity in the range of 17-58 vol.% and pore size up to 800 microm were produced by controlling LENS parameters, which showed a broad range of mechanical strength of 24-463 MPa and a low Young's modulus of 2.6-44GPa. The effects of porous structure on bone cell responses were evaluated in vitro with human osteoblast cells (OPC1). The results showed that cells spread well on the surface of porous Ti and formed strong local adhesion. MTT assay indicated LENS processed porous Ti provides a preferential surface for bone cell proliferation. Porous Ti samples also stimulated faster OPC1 cell differentiation compared with polished Ti sheet, which could be due to the change in cell morphology within the pores of Ti samples. More extracellular matrix and a higher level of alkaline phosphatase expression were found on the porous samples than on the Ti sheet. This can be beneficial for faster integration of porous implant with host bone tissue. The results obtained also indicated that a critical pore size of 200 microm or higher is needed for cell ingrowth into the pores, below which OPC1 cells bridged the pore surface without any growth in the pores.
Microstructure of thermal sprayed hydroxyapatite (HA) splats was characterized using transmission electron microscopy (TEM), and the formation mechanisms of micropores within the splats were investigated with the aid of simulated body fluids (SBF). High-velocity oxy-fuel and direct current (DC) plasma spray techniques were both utilized for the splats' deposition. The microstructure features of individual HA splats were revealed through TEM observation of as-sprayed, and ion-milled splats. Amorphous calcium phosphate and tricalcium phosphate phases were observed at the splats' fringes, which indicated that extensive decomposition of HA had occurred at these locations. The fringes of the HA splats are essentially nanostructured ( approximately 20-50 nm grains), while calcium phosphate grains up to 5 microm, depending on flattening state, are present at the center of the splats. Morphological observation classified the pores within the HA splats into three main categories according to distinctive features in their microstructure: open pores, sealed pores and through-thickness pores. It was found that particle velocity with which the particle impinged on the substrate surface, particle melt state, and structure of starting particle (mainly porosity) are the key variables in determining the formation and morphology of the micropores within the flattened splats. Influence of subsequent splats on the pores of prior deposited splat was also studied using an in vitro incubation test in SBF. Obvious pore-sealing action on the open pores was revealed, which was achieved through liquid filling of subsequent droplets. It was postulated that the overall porosity of a bulk coating could be attributed primarily to the sealed pores and flaws among the splats, and, it could be adequately governed through appropriate particle melt state and optimized velocity of the particles during coating formation.