Article

Design, selection and characterization of novel glasses and glass-ceramics for use in prosthetic applications

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Abstract

The objective of this work is to design and characterize crystallizable silicate and borosilicate compositions for use in the production of smart, unconventional coatings on bioceramic implants. The concept behind this research is the development of a three-layer implantable system (joint prosthesis) comprising a ceramic substrate, a glass-derived trabecular coating and a glass-ceramic interlayer that joins the other two elements together. The outer porous coating should exhibit bone-like architecture, high mechanical strength and good bioactivity to bond to bone, whereas the interlayer should be chemically stable in biological fluids to avoid detachment between the joined parts. Glasses in the SiO2-Na2O-K2O-CaO-P2O5-B2O3-Al2O3 system have been synthesized by a melting route and thermally treated to obtain glass-ceramic products. A selection of potentially suitable materials for the trabecular coating and interlayer was carried out on the basis of thermal properties and tendency to dissolve in simulated body fluids (SBF) so that the integrity of the final device might be maintained upon implantation. The glass selected for the trabecular coating was processed by sponge replica method to produce glass-ceramic scaffolds, in order to evaluate the material properties and performance in an embodiment plausibly close to the final application. The mechanical properties of the porous glass-ceramic, which mimicked the 3-D pore architecture of cancellous bone, were adequate for load-bearing applications such as joint prostheses. Formation of a surface apatite layer on scaffold struts upon soaking in SBF confirmed the excellent bioactivity of the material, which is a key precondition for in vivo osteointegration. © 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

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... The glass bioactivity and the width of the processing window present opposite dependence on the silica network connectivity; therefore, the selected glass chemistry must provide a compromise between bioactivity and processing window. The Hruby Hr parameter has been proposed to quantify the processing window, this parameter relates the glass vitreous state stability with the crystallization tendency [34,35]. Table 14.2 collects different BG compositions applied in LC and LDGD. ...
... Thus, the glass-ceramic coating would be subjected to compressive stresses after cooling. This situation is difficult to attain due to the relatively high coefficient of thermal expansion of most of the BGs, several BG alternative compositions with lower coefficient of thermal expansion have been proposed [35,40]. The S50B2 is a BG with a slightly narrower working window in comparison to S520 BG, but with a lower coefficient of thermal expansion due to the Na 2 O and K 2 O content and B 2 O 3 addition [40]. ...
... The coatings show sound interface bonding and the behavior in vitro. Moreover, the coatings present intact BG apatite formation ability, and it is reported excellent biocompatibility in contact to mesenchymal stem and osteoblast-like cells [22,23,35]. ...
Chapter
This chapter covers the production of bioactive glass‐ceramic coatings by laser cladding and the additive fabrication of bioactive glass‐ceramics by laser direct glass deposition. The laser cladding technique and the laser direct glass deposition techniques are introduced and their applications in the ceramic biomaterials field are presented. Fundamentals of laser‐material interaction and current technology for coating production and additive manufacturing are reviewed. A deep analysis of the requirements of the bioactive glasses and their properties as precursor materials for laser assisted processing is provided, in addition to the explanation of the reported structural and bioactivity changes. Finally, the impact of processing conditions on the mechanical and bioactive properties of the laser additive manufacturing are described.
... A fundamental presupposition for a successful hard tissue implantation is a continuation at the interface between the implant and the living part. The HA layer formed onto the surface of bioactive glasses or ceramics serves a dual aim, where the optimum combination of these two functions [6,10,17,18] and dental implant materials of zirconia and Ti-alloys [9,10,12,30]. Dentine 230-305 15-30 <0. ...
... A fundamental presupposition for a successful hard tissue implantation is a continuation at the interface between the implant and the living part. The HA layer formed onto the surface of bioactive glasses or ceramics serves a dual aim, where the optimum combination of these two functions [6,10,17,18] and dental implant materials of zirconia and Ti-alloys [9,10,12,30]. Dentine 230-305 15-30 <0. 6 3 [6] Cortical bone 50-150 7-30 0.06-0.075 ...
... 6 3 [6] Cortical bone 50-150 7-30 0.06-0.075 2-12 [6,10,17,18] Trabecular bone 10-20 0.05-0.5 0.5-1 0.7-1.1 [17,18] Zirconia >500 210 12 6-10 [9, 10, 12, 30] Ti alloys >1200 105-110 2.2-4 - [9,10] In dental implant applications, the most popular materials used, such as titanium (Ti) or zirconia, are non-bioactive or bioinert. Like any other dental material, Ti has some minor drawbacks. ...
Chapter
This chapter reports on novel glass‐ceramics (GCs) in the CaO–MgO–SiO 2 ternary system with additives of Na 2 O/K 2 O, P 2 O 5 , and CaF 2 , which aim at dental implant applications. The design of the composition of the glasses was based on two well‐established – by our research team – parent compositions, which, in glass state, exhibit excellent bioactivity performance, in vitro , in vivo , as well as in clinical trials. In order to approach the mechanical properties of natural tissues, complete substitution of K 2 O for Na 2 O and partial substitution of MgO for CaO in the parent compositions took place. The GCs were produced by sintering and controlled crystallization of glass‐powder compacts in the temperature interval of 800–900 °C, according to the results of thermal analysis. The properties of the produced GCs discussed in this chapter are the sintering behavior and the crystallization mechanism, along with their mechanical properties, aesthetics, and bioactivity, which allows evaluating their suitability for dental implant applications. Good matching of the properties of these GCs with those of the natural dental tissues was achieved. Most importantly, the substitutions effectively allowed the tuning of the mechanical properties of these bioactive GCs in order to approach the properties of the natural hard tissues, such as jaw bone and dentine.
... EDS analyses, performed on the reaction layers upon 14-day exposure to SBF in mild shaking ( Figure 5) and static ( Figure 6) conditions, confirmed the formation of a reaction bilayer (silica gel + calcium phosphate) with a Ca/P ratio of 1.48 in the silica-rich region and 1.55 on the top surface. The latter value is quite close to the Ca-to-P ratio of stoichiometric HA (1.67) and suggests the formation of Ca-deficient HA, as reported in other previous studies on other silicate BG compositions [36][37][38]. A 30 µm-thick silica gel layer, which typically forms on the surface of BGs upon immersion in SBF [33], was observed on the inner surface of the scaffold pores (white arrow in Figure 4b-e), thus indicating the progressive conversion of the material to a calcium phosphate layer (yellow arrows in Figure 4b-e), as also confirmed by the compositional analysis through EDS (Figures 5 and 6). ...
... EDS analyses, performed on the reaction layers upon 14-day exposure to SBF in mild shaking ( Figure 5) and static ( Figure 6) conditions, confirmed the formation of a reaction bilayer (silica gel + calcium phosphate) with a Ca/P ratio of 1.48 in the silica-rich region and 1.55 on the top surface. The latter value is quite close to the Ca-to-P ratio of stoichiometric HA (1.67) and suggests the formation of Ca-deficient HA, as reported in other previous studies on other silicate BG compositions [36][37][38]. ...
... EDS analyses, performed on the reaction layers upon 14-day exposure to SBF in mild shaking ( Figure 5) and static ( Figure 6) conditions, confirmed the formation of a reaction bilayer (silica gel + calcium phosphate) with a Ca/P ratio of 1.48 in the silica-rich region and 1.55 on the top surface. The latter value is quite close to the Ca-to-P ratio of stoichiometric HA (1.67) and suggests the formation of Ca-deficient HA, as reported in other previous studies on other silicate BG compositions [36][37][38]. It is universally recognized that the formation of HA in a simulated physiological environment represents a valuable and affordable criterion to preliminarily evaluate the bioactive potential of biomaterials; although, being aware that in vitro conditions can only roughly match those in the human body. ...
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Article
Bioactive glasses are often designed as porous implantable templates in which newly-formed bone can grow in three dimensions (3D). This research work aims to investigate the bone regenerative capability of silicate bioactive glass scaffolds produced by robocasting in comparison with powder and granule-like materials (oxide system: 47.5SiO2-10Na2O-10K2O-10MgO-20CaO-2.5P2O5, mol.%). Morphological and compositional analyses performed by scanning electron microscopy (SEM), combined with energy dispersive spectroscopy (EDS) after the bioactivity studies in a simulated body fluid (SBF) confirmed the apatite-forming ability of the scaffolds, which is key to allowing bone-bonding in vivo. The scaffolds exhibited a clear osteogenic effect upon implantation in rabbit femur and underwent gradual resorption followed by ossification. Full resorption in favor of new bone growth was achieved within 6 months. Osseous defect healing was accompanied by the formation of mature bone with abundant osteocytes and bone marrow cells. These in vivo results support the scaffold’s suitability for application in bone tissue engineering and show promise for potential translation to clinical assessment.
... Another important issue about bioactive glass coatings concerns their thermal properties: When a coating is applied, the thermal expansion coefficient (CTE) of the glass should match that of the substrate to prevent the glass pulling away from the base implant upon processing [17]. The CTE of the wellknown 45S5 Bioglass Ò (15 9 10 -6°C-1 ; SiO 2 -CaO-Na 2 O-P 2 O 5 system) is significantly higher than that of titanium alloys (9 9 10 -6°C-1 ) and alumina (8 9 10 -6°C-1 ) which are commonly used to fabricate orthopedic and dental implants: therefore, the need has emerged to develop new glass formulations with a more suitable CTE for use as coating materials [18]. ...
... Partial replacement of Na 2 O and CaO with K 2 O and MgO, respectively, was the most common strategy to tailor the CTE of the glass [19]. B 2 O 3 can be also incorporated in the glass formulation to decrease the CTE, although bioactive borosilicate glasses show an increased tendency toward dissolution in aqueous media (including biological fluids) [18]. Gomez-Vega et al. [19] suggested that multiple glass layers of different compositions may be helpful in achieving a good compromise among thermal behavior, optimal dissolution rate, and bone integration. ...
... Criteria of design and selection of these glasses are described elsewhere in detail [18]. S57A7 and S50B2 glasses were manufactured by melting mixes of high-purity raw materials (oxides and carbonates) in platinum crucibles. ...
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Article
Deposition of bioceramic coatings on medical implants is a valuable strategy to impart key added values, such as bioactivity. While flat coatings can be easily produced by enameling and similar techniques, applying a bioactive glass layer on surfaces with curved geometry is a great challenge from a technological viewpoint. In this work, for the first time we demonstrated the feasibility of bioactive glass coatings produced by laser cladding on alumina/zirconia ceramic acetabular cups for hip joint prosthesis. Laser-cladded glass coatings can be fabricated in a dense (pore-free) or porous form. Morphological analyses by scanning electron microscopy and micro-computed tomography revealed the good quality of joining at the coating/substrate interface and the good interconnectivity of the pores (size within 200–400 µm) in the outer porous layer. Indentation tests at the interface confirmed the excellent joining between glass and ceramic substrate. These coatings also exhibited a good bioactive behavior in vitro, as demonstrated by the formation of a surface apatite layer upon immersion studies in simulated body fluid.
... It is also successfully implemented in areas of skin and muscle regeneration. Interestingly, different studies have highlighted variety of innovative applications coming up in bioactive glass and glass ceramics that could enhance bone and tissue engineering of wound healing and soft tissue engineering (Pachecco et al. 2015;Baino et al. 2016). This review highlights the current types of scaffolds, their uses, advantages and limitations in stem cells tissue engineering applications and in regenerative medicine. ...
... This new emerging approach has put forward the use of glass-derived scaffolds as osteointegrative trabecular coatings on ceramic acetabular cup of hip joint prosthesis. The coating will activate and induce biological fixation of the prosthesis and at the same time removes the need for invasive screws, or threading to fix implants in place (Vitale-Brovarone et al. 2012;Baino et al. 2015Baino et al. , 2016. ...
... A part from the traditional use for osseous defect repair, a variety of innovative applications are proliferating. Currently, studies have highlighted the significant of bioactive glasses and glass-ceramics for wound healing applications and soft-tissue engineering (Baino et al. 2016;. ...
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Article
Nowadays, there has been immense progress in developing materials to support transplanted cells. Nevertheless, the complexity of tissues is far beyond what is found in the most advanced scaffolds. This article reviews the types of biomaterials and their resulting scaffolds in the bio-engineering of bone and tissues by presenting an overview of the characteristics of ideal scaffold in tissue engineering along with types of scaffolds and examples of previous studies where these scaffolds have been applied. The advantages of scaffolds, and the three-dimensional culture system and its used commercially available scaffold is presented. Challenges encountered in the application of these scaffolds in bone and tissue engineering is also highlighted. Used method was by acquisition of materials through Google scholar, Science direct, PubMed and University library archives. Proper knowledge of the above highlighted facts will go a long way in re-addressing the production of scaffolds for bone and tissue engineering. With the proliferation of innovative applications in bioactive glasses and glass ceramics, the greater need for specific understanding of cell biology with emphasis on cellular differentiation, cell to cell interaction and extracellular matrix formation in engineering of bone and tissues becomes inevitable. This will enhance scaffold production, bone regeneration and transplantation outcome.
... Two glass compositions were adopted to manufacture the dense coating (S57A7, 57SiO 2 -30CaO-6Na 2 O-7Al 2 O 3 mol%) and the trabecular layer (S50B2, 50SiO 2 -35CaO-7Na 2 O-6P 2 O 5 -2B 2 O 3 mol%), respectively. Criteria of design and selection as well as the characterization of these glasses are reported elsewhere [32]. S57A7 and S50B2 were individually manufactured and the mixed high-purity raw materials (oxides and carbonates) added to platinum crucibles for subsequent melting. ...
... Sponge replication allows the fabrication of porous ceramic products by using a polymeric sponge as a sacrificial template that is soaked in the slurry, squeezed to remove the excess suspension from the pores and eventually burnt-out to obtain an inorganic replica of the 3-D foam structure [33,34]. This technique is generally recognized as a highly effective and versatile method to process bioactive glasses in the form of bone-like porous scaffolds [32], and early results attained in previous studies by our research team demonstrated the suitability of this method to fabricate trabecular coatings on flat prosthetic implants [26,27]. In order to effectively apply the trabecular coating to a "real" bioceramic cup that is to be used in hip joint surgery, there were two key questions to answer: (i) how to impart a shell-like shape to the porous polymeric template?, and (ii) how to remove the excess slurry from the pores of the polymeric foam in this particular configuration? ...
... Full characterization of S57A7 and S50B2 glasses, including the glass-ceramic products obtained from them after sintering, has been reported elsewhere [32]. ...
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Article
Over the last 25 years, the philosophy behind an optimal fixation of orthopaedic implants to hard tissues progressively evolved towards “bone-conservative” solutions in order to minimize bone resection/loss and maximize tissue-implant integration. Hence, the researchers’ attention moved from “traditional” fixation of the prosthesis to host bone by using screws or acrylic cement to new strategies based on physico-chemical bonding and surface modification of the implant. This research work explores the feasibility of a novel bioceramic monoblock acetabular cup for hip joint prosthesis that can be fixed to the patient’s bone by means of a bone-like trabecular coating able to promote implant osteointegration. Sponge replica method was properly adapted and optimized to produce hemispherical foam-like bioactive glass-ceramic coatings that were joined to Al2O3/ZrO2 composite cups by the interposition of a glass-ceramic interlayer. Morphological analyses by scanning electron microscopy (SEM) and micro-computed tomography revealed the good quality of joining at the different interfaces. Preliminary investigation of the mechanical properties was carried out to evaluate the suitability of the device for biomedical use. In vitro bioactive behaviour was assessed by immersion studies in simulated body fluid and evaluating the apatite formation on the struts of the trabecular coating. The concepts and findings reported in the present work can have a significant impact in the field of implantable devices, suggesting a valuable alternative to currently-applied but often suboptimal techniques for bone-prosthesis fixation.
... Other studies have also addressed the impact of B 2 O 3 addition on TEC, demonstrating that, although borosilicate glasses are characterized by a higher dissolution rate than silicate glasses in an aqueous environment, they exhibit lower TEC values [209]. The adhesion between the BG coating and the metallic implant can be evaluated through scratch tests, usually followed by morphological analysis by optical microscopy or SEM, tensile (pull-out) tests or nanoindentation tests [210]. ...
... The use of glass/glass-ceramic coatings on metallic implants has not achieved yet a full translation into clinical practice mainly due to some issues, including TEC-related interfacial delamination and coating stability in the long term (BGs tend to undergo progressive dissolution over time, thus leading to implant failure); however, many efforts have been made by several research groups to develop glass/glass-ceramic materials for this application [202,209]. ...
Article
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.
... Several different BSMs were developed and artificially produced for bone grafting, i.e., biocompatible polymers, metals, ceramics/glasses, and composites [3]. Bioactive glasses (BGs) exhibit very attractive properties as materials for bone tissue engineering (BTE) thanks to their bonding ability at the implant/bone interface through precipitation of a hydroxyapatite (HA) layer [4]. Man-made materials for BTE are often produced as porous scaffolds, which should fulfill specific requirements in terms of biological features, porosity, and mechanical properties to achieve a good implant outcome [5]. ...
... In 2014, Eqtesadi et al. sintered vitreous scaffolds using a carboxymethyl cellulose-based ink. They obtained scaffolds that exhibited compressive strength (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13) and porosity (60-80 vol.%) comparable to those of the trabecular bone [20]. The same group investigated the effect of devitrification on scaffold bioactivity in 2017 by comparing amorphous scaffolds, sintered at 550 °C, and mostly crystalline structures processed at 1000 °C. ...
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Article
: Additive manufacturing of bioactive glasses has recently attracted high interest in the field of regenerative medicine as a versatile class of fabrication methods to process bone substitute materials. In this study, melt-derived glass particles from the SiO2-P2O5-CaO-MgO-Na2O-K2O system were used to fabricate bioactive scaffolds with graded porosity by robocasting. A printable ink made of glass powder and Pluronic F-127 (binder) was extruded into a grid-like three-dimensional structure with bimodal porosity, i.e., the inner part of the scaffold had macropores with smaller size compared to the periphery. The crystallization behavior of the glass powder was studied by hot-stage microscopy, differential thermal analysis, and X-ray diffraction; the scaffolds were sintered at a temperature below the onset of crystallization so that amorphous structures could be obtained. Scaffold architecture was investigated by scanning electron microscopy and microtomographic analysis that allowed quantifying the microstructural parameters. In vitro tests in Kokubo’s simulated body fluid (SBF) confirmed the apatite-forming ability (i.e., bioactivity) of the scaffolds. The compressive strength was found to slightly decrease during immersion in SBF up to 4 weeks but still remained comparable to that of human cancellous bone. The pH and concentration of released ions in SBF were also measured at each time point. Taken together, these results (favorable porosity, mechanical strength, and in vitro bioactivity) show great promise for the potential application of these robocast scaffolds in bone defect repair.
... The mechanical suitability of these materials for potential use in prosthetic and bone implant applications was evaluated in previous studies [16,32]. Tensile (pull-out) tests allowed the authors to determine that the adhesion strength of S57A7 coatings on alumina was about 27 MPa [16]. ...
... Two glass formulations (Table 1) were selected to produce multi-layered coatings on the alumina/zirconia composite substrates. The rationale behind the design of these glass compositions and the relevant characterization results are described elsewhere [32]. Both glasses were produced by using a standard melting method in a platinum crucible. ...
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Article
Achieving the stable osteointegration of prosthetic implants is one of the great challenges of modern orthopedic surgery. The fixation of ceramic acetabular cups of hip joint prostheses is usually achieved using a metal shell provided with screws or pegs that penetrate into the host pelvic bone. The deposition of bioactive coatings on the implant surface to be put in contact with bone could be a valuable strategy to promote a more “physiological” osteointegration. In this work, bioactive glass porous coatings were manufactured on the top of alumina/zirconia composite implants by two different methods, i.e., sponge replication and laser cladding. The coated samples underwent immersion studies in Kokubo’s simulated body fluid (SBF) to assess in vitro bioactivity and were found to exhibit an excellent hydroxyapatite-forming ability, which is key to allow bonding to bone. Biological tests using mesenchymal stem and osteoblast-like cells revealed the good biocompatibility of both types of materials. Furthermore, a higher level of mineralization was induced by the sponge-replicated coatings at 10 days. Overall, these results are highly promising and encourage further research on these materials.
... Thermal-sprayed HA coatings on metal joint prostheses are also used in the clinical practice by surgeons (Sun et al., 2001). Bioactive glass-ceramic porous coatings on alumina acetabular cups have been recently proposed to improve osteointegration of prosthetic devices (Vitale-Brovarone et al., 2012b;Baino et al., 2015Baino et al., , 2016a. All the applications of bioactive ceramics take the advantage of bioactivity and minimize mechanical-property requirements, which may be an issue in the case of highly porous implants. ...
... In this regard, a fascinating approach that has been put forward is the use of glass-derived scaffolds as osteointegrative trabecular coatings on ceramic acetabular cup of hip joint prosthesis. These coatings are expected to induce biological fixation of the prosthesis while eliminating the need for invasive screws, cements, or threading to fix implants in place (Vitale-Brovarone et al., 2012b;Baino and Vitale-Brovarone, 2015b;Baino et al., 2015Baino et al., , 2016a. ...
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Article
In the last few decades, we have assisted to a general increase of elder population worldwide associated with age-related pathologies. Therefore, there is the need for new biomaterials that can substitute damaged tissues, stimulate the body’s own regenerative mechanisms, and promote tissue healing. Porous templates referred to as “scaffolds” are thought to be required for three-dimensional tissue growth. Bioceramics, a special set of fully, partially, or non-crystalline ceramics (e.g., calcium phosphates, bioactive glasses, and glass–ceramics) that are designed for the repair and reconstruction of diseased parts of the body, have high potential as scaffold materials. Traditionally, bioceramics have been used to fill and restore bone and dental defects (repair of hard tissues). More recently, this category of biomaterials has also revealed promising applications in the field of soft-tissue engineering. Starting with an overview of the fundamental requirements for tissue engineering scaffolds, this article provides a detailed picture on recent developments of porous bioceramics and composites, including a summary of common fabrication technologies and a critical analysis of structure–property and structure–function relationships. Areas of future research are highlighted at the end of this review, with special attention to the development of multifunctional scaffolds exploiting therapeutic ion/drug release and emerging applications beyond hard tissue repair.
... Several authors have reported that borate and borosilicate bioactive glasses show higher dissolution nature [11,12]. To improve the properties of the glass system, some of the transition elements are the best candidates which can be incorporated during the synthesis process. ...
Article
The main purpose of the present investigation is to examine in detail in vitro studies like bioactivity and cytocompatibility of a novel bioactive glass system i.e., B2O3–SiO2–Na2O–CaO–ZnO glass composition. Glasses are prepared by the traditional melt quenching method. In vitro studies are performed with ISO standards. Bioactivity has been studied using standard Kokubo’s method. Highly sophisticated analytical techniques were utilized for the assessment of apatite forming ability. Scanning electron microscopy micrographs have shown visible evidence of apatite forming ability through cauliflower type of precipitation on the surface of the glass. Cytocompatibility was performed using human osteoblast cells (MG-63). Cytocompatibility of zinc-containing soda lime borosilicate glasses has shown significant results for bone tissue engineering applications.
... The observed Raman bands in the low-frequency region of 550-750 cm − 1 further support these assignments. More specifically, the Si-O-Si bending motions in Q 2 units result in the band at ~630 cm − 1 [43][44][45]. Additionally, the asymmetry of this band towards high frequencies is ascribed to bend vibrations of S-O − bonds of various Q n units bearing NBOs [46]. ...
Article
Novel glasses in CaO-MgO-SiO2 system with Na2O, P2O5, and CaF2 additives were produced by melting/quenching technique. The influence of K2O and MgO on glass structure, the thermal properties (of major importance for evaluating the crystallization mechanism), and properties related to their potential in biomedicine (bioactivity, machinability), was investigated. According to Raman spectra, K2O for Na2O substitution favors the formation of Q⁰ and Q¹ silicate units at the expense of Q² and Q³ ones, whereas substitution of MgO for CaO increases the Q² and Q³ units at the expense of Q¹ ones. The presence of K2O caused the increase of Tg and of the crystallization temperature as well as of the Ea of crystallization. A weaker influence on the above magnitudes was recorded in glasses with MgO substitution. The produced glasses are generally prone to 3-dimensional crystallization, display bioactivity in SBF testing, and manifest positive value of the machinability parameter n.
... The demand for glass-ceramic (GC) components obtained by prototyping techniques, such as Computer-Aided Design/Computer-Aided Machining (CAD/CAM) milling, has considerably increased in recent years, especially for bio-related applications that require reliable design, such as dental crowns, non-metallic dental implants, intraocular substitutes, and middle ear ossicles (Abd El-Ghany and Sherief, 2016; Baino et al., 2016;Crovace et al., 2016;Kaur et al., 2019;Montazerian and Zanotto, 2017). Lithium silicate GCs have been established for some decades in the manufacture of dental prostheses because of their biocompatibility, mechanical strength, chemical durability, reliability, and excellent machinability (Soares et al., 2015;Zhang et al., 2014). ...
Article
Objectives This study aimed to optimize the crystallization process and the microstructure of a new bioactive glass-ceramic (GC) previously developed by our research group to obtain machinable glass-ceramics. Methods Differential scanning calorimetry (DSC) analyses were conducted to explore the characteristic temperatures and construct a semi-quantitative nucleation curve. The GC specimens were characterized by X-ray diffraction (XRD) and Rietveld refinement. Their brittleness index (B) and machinability were characterized and compared with IPS e.max-CAD®. Their Young's modulus, fracture toughness, and hardness were assessed. Results We found that the maximum crystal nucleation rate temperature of this GC is ∼470 °C. Treatments were designed based on the 1st DSC peak onset (570 °C), 1st peak offset (650 °C), and 2nd peak offset (705 °C) crystallization temperatures of lithium metasilicate (LS, LiSi2O3) and lithium disilicate (LS2, Li2Si2O5). Rietveld refinement indicated an increase in LS2 and a reduction in LS and amorphous phase for increased temperatures and longer treatment times. Their B values indicate good machinability compared with that of the control group based on statistical analyses. As expected, lower levels of LS2 increase the machinability regardless of the rotation speed adopted, leading to a greater depth of cut and reduced Edge Chipping Damage Depth (ECDD). Conclusion This bioactive GC with optimized microstructure presents high machinability. For treatment temperatures above 570 °C, the number of elongated LS2 crystals increases and decreases the amorphous phase content, which reduce the machinability of the GC, and should therefore be avoided. The best results were obtained using heat treatment at 570 °C, which produces LS crystals embedded in a glassy matrix (67%) with small contents of secondary phases.
... They are being used broadly for biomedical requests as orthopedic implant and bone filler materials, as a result of their biocompatibility and tight bonding with bone [2 , 3]. The bioactive glass-ceramics have a significant place in the biomedical application, due to their higher mechanical strength compared to the derived glass thanks to their unique microstructure [4][5][6]. Moreover, they are capable to bond with the living bone directly by the growth of healthy tissue onto their surface through a biologically active hydroxycarbonate apatite (HCA) layer without aformation of surrounding fibrous tissue. ...
Article
The effect of introducing Na-Ca-phosphate (NCP) and/or fluorapatite in the bioactive wollastonite-diopside (WD) was investigated in this study. The prepared materials were characterized by DTA, XRD, and SEM/EDX. Moreover, the density and Vicker's microhardness were measured. The in vitro bioactivity test was carried out in SBF, and the cell viability test was evaluated using the Vero cells. The results showed that NCP-containing WD glass-ceramic was showed the lowest density value due to its low densification, and accordingly, it showed the lowest Vicker`s microhardness value. Furthermore, combining Na-Ca-phosphate in WD was increased the cell viability better than that included fluorapatite, whereas, the combination of both crystalline phases led to increase the cytotoxicity to the highest value. In conclusion, different properties of wollastonite-diopside glass-ceramics can be tailored. Hence, these glass-ceramics are expected to be useful materials in promising biomedical applications, such as orthopedics and dentistry.
... The bioactive glass-ceramics have a signi cant place in the biomedical application, due to their higher mechanical strength compared to the derived glass thanks to their unique microstructure [4][5][6] . Moreover, they are capable to bond with the living bone directly by the growth of healthy tissue onto their surface through a biologically active hydroxycarbonate apatite (HCA) layer without the formation of surrounding brous tissue. ...
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In this study, we investigated the effect of introducing sodium calcium phosphate (NCP), fluorapatite (FA), or the combination of both phases in the wollastonite-diopside (WD) bioactive glass-ceramic system on the crystalline phases formed, microstructure, degradation, and biocompatibility of those materials. The prepared materials were characterized by DTA, XRD, and SEM/EDX. Moreover, the density was measured via Archimede’s method, and the mechanical properties were measured by Vicker’s microhardness indenter. The in vitro bioactivity test was carried out in the simulated body fluid (SBF), and the cell viability test was evaluated using the Vero cells. The results showed that the formed crystalline phases were close to the starting proposed phases. Moreover, NCP-containing WD glass-ceramic was showed the lowest density value due to its low densification, and accordingly, it showed the lowest Vicker`s microhardness value due to the same reason. Furthermore, combining sodium calcium phosphate in WD glass-ceramic was increased cell viability better than that included fluorapatite, whereas, the combination of both crystalline phases in WD glass-ceramic led to an increase in the cytotoxicity to the highest value. In conclusion, different properties of wollastonite-diopside glass-ceramics can be tailored by the combination of NCP or FA, and hence, these glass-ceramic materials can be modified effectively according to the purpose for which it is intended to be applied. The obtained results indicated that different properties of WD glass-ceramic materials can be tailored by the combination of NCP and/or FA. Hence, these glass-ceramics are expected to be useful materials in promising biomedical applications, such as orthopedics and dentistry.
... The discovery of the bioactive glass 45S5, by Prof. Hench 50 years ago, inaugurated the field of modern bioactive glasses and ceramics [1]. These materials are able to spontaneously transform their surface into a hydroxyapatite (HA) layer, when they are in a biological environment, either natural (i.e. in the body) or artificial (e.g. in simulated body fluid, SBF) [2][3][4][5][6]. Assuming that a successful hard tissue implantation produces the result of a continuation at the interface between the implant and the living part, the HA layer formed onto the surface of the bioactive glasses or ceramics serves a dual purpose, where the optimum combination of these two functions is the key to the success of an implantation. ...
Article
This paper reports on the development of novel bioactive glass-ceramics (GCs) in the Na2O/K2O-CaO-MgO-SiO2-P2O5-CaF2 system for dental implant applications. The influence of partial substitution of Mg for Ca and of complete substitution of K for Na on bioactivity performance, mechanical properties, and aesthetics, was thoroughly investigated. Dense and well-crystallized GCs were produced, where the K-free GCs were comprised of diopside, wollastonite, and fluorapatite, and the K-containing ones consisted of diopside, fluorapatite, and alpha-potassium magnesium silicate (α-PMS). The experimental results suggest that wollastonite and α-PMS favored the bioactivity performance, reflected in the ability of the GCs to spontaneously form hydroxyapatite on their surface. It was also demonstrated that the above substitutions in the produced GCs enable suitable tuning of their mechanical properties in order to approach the physical properties of natural jaw bones (i.e. reduction of modulus of elasticity, increase of fracture toughness) better than the commercial zirconia and titanium implants.
... The Ca/P atomic ratio after 1-week immersion in SBF was around 0.5 ± 0.24 (measurements performed on three points), which is remarkably lower than the stoichiometric value of HA (1.67). Calcium-deficient HA was already observed on the surface of bioactive glasses with several compositions [52][53][54]. It is believed that a further increase of the Ca/P ratio is likely to be observed by extending the duration of the test up to 14-21 days, as already done in our previous work on 3D-printed glass scaffold with the same composition [55]. ...
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In recent years, bioactive glasses gained increasing scientific interest in bone tissue engineering due to their capability to chemically bond with the host tissue and to induce osteogenesis. As a result, several efforts have been addressed to use bioactive glasses in the production of three-dimensional (3D) porous scaffolds for bone regeneration. In this work, we creatively combine typical concepts of porous glass processing with those of waste management and propose, for the first time, the use of bread as a new sacrificial template for the fabrication of bioactive scaffolds. Preliminary SEM investigations performed on stale bread from industrial wastes revealed a suitable morphology characterized by an open-cell 3D architecture, which is potentially able to allow tissue ingrowth and vascularization. Morphological features, mechanical performances and in vitro bioactivity tests were performed in order to evaluate the properties of these new “sustainable” scaffolds for bone replacement and regeneration. Scaffolds with total porosity ranging from 70 to 85 vol% and mechanical strength comparable to cancellous bone were obtained. Globular hydroxyapatite was observed to form on the surface of the scaffolds after just 48-h immersion in simulated body fluid. The results show great promise and suggest the possibility to use bread as an innovative and inexpensive template for the development of highly-sustainable bone tissue engineering approaches.
... Conventional bioglasses are soda lime silicophosphate based amorphous materials, compatible with living tissues, bond to bone. But, recent days borate [1] and borosilicate [9,10] based glass materials have increased because of the encouraging clinical results in human healthcare. ...
... The scaffolds could act as templates in developing the new tissues. The bioactive glass and glass ceramics could also improve the wound amendment [13,14]. ...
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Article
The fabrication of novel scaffolds was represented on the basis of conductive and biodegradable copolymers. The star-like polycaprolactone (S-PCL) was synthesized from dipentaerythritol as a core by a catalyst of Sn(oct)8 through ring-opening technique. After functionalization of S-PCL by thiophene, thiophene monomer was polymerized from polycaprolactone ends via chemical oxidation polymerization to reach star-like polycaprolactone–polythiophene (S-PCL–PTh). The scaffolds demonstrated a porous configuration (160–190 nm) having the great surface area as well as conductivity of 0.011 S cm−1. The cytocompatibility measurements exhibited that the nanofibers were not toxic to the MG63 cells.
... e Ca-to-P atomic ratio increases with soaking time from 0.46 at 24 h to 1.47 at 2 weeks. e Ca-to-P ratio at the end of the experiments is still lower that the value of stoichiometric HA (Ca/P � 1.67), revealing the presence of Ca-deficient HA as already observed previously for other bioactive glass compositions [46][47][48]. However, as Mg 2+ ions are released from the glass surface during immersion in SBF, a small amount of Ca in HA has been substituted by Mg, as confirmed by compositional analysis. ...
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Article
Bioactive silicate glass scaffolds were fabricated by a robocasting process in which all the movements of the printing head were programmed by compiling a script (text file). A printable ink made of glass powder and Pluronic F-127, acting as a binder, was extruded to obtain macroporous scaffolds with a grid-like three-dimensional structure. The scaffold architecture was investigated by scanning electron microscopy and microtomographic analysis, which allowed quantifying the microstructural parameters (pore size 150–180 μ m and strut diameter 300 μ m). In vitro tests in simulated body fluid (SBF) confirmed the apatite-forming ability (i.e., bioactivity) of the scaffolds. The compressive strength (around 10 MPa for as-produced scaffolds) progressively decreased during immersion in SBF (3.3 MPa after 4 weeks) but remains acceptable for bone repair applications. Taken together, these results (adequate porosity and mechanical strength as well as bioactivity) support the potential suitability of the prepared scaffolds for bone substitution.
... For instance, it was widely shown that the addition of monovalent and bivalent modifiers (e.g. K 2 O, Na 2 O, CaO and MgO) is useful to adjust the rate of the bioactivity process in silicate glasses [88] and/or the resorption of phosphate glasses [42], and small amounts of Al 2 O 3 (< 3 mol%) are helpful to increase the mechanical properties of the glasses [147]. Furthermore, small amounts of trace elements can be embedded in the glass composition so that, once released, can elicit an appropriate therapeutic effect in situ. ...
Article
Over the millennia, men have continuously potentiated their abilities through developing and applying new materials and technologies. A number of metallic, ceramic and polymeric implants have been experimented as “spare parts” to restore lost functions or organs in the body. Till the 1960s, the selection of potentially suitable prosthetic materials was based on the criterion of maximum biological and biochemical inertness in contact with body fluids. Fifty years ago, the invention of the first bioactive glass, which was able to create a strong bond with living bone, radically changed this concept and paved the way for the advent of the modern era of biomaterials science. Since then, a number of bioactive glass-based products, such as small solid blocks, fine particles, granules, porous scaffolds and injectable putties, have been implanted in millions of patients primarily to repair bone and dental defects. Over the last decade, bioactive glasses have also shown promise in highly fascinating, emerging applications that involve angiogenesis (e.g. wound healing), interfacial hard-soft tissue engineering and controlled drug delivery. This review offers the reader a “guided tour” in the field of bioactive glass science and technology, also highlighting the future challenges to be met by materials scientists, bioengineers and clinicians to further exploit the benefits associated to these ever-surprising materials, which were unthinkable when research began.
... Worldwide many researchers have used the SiO 2 -Na 2 O-CaO-P 2 O 5 system as a template for developing new silica-based compositions [7]. Subsequently, many formulations in the phosphate and borate-based system have been also designed to overcome the Bioglass® and silicatebased glass limitations [8][9][10][11], and thus to meet the set of requirements that are both crucial and necessary for optimised tissue-engineered substitutes [12]. ...
Article
Eight novel silicate, phosphate and borate glass compositions (coded as NCLx, where x = 1 to 8), containing different oxides (i.e. MgO, MnO2, Al2O3, CaF2, Fe2O3, ZnO, CuO, Cr2O3) were designed and evaluated alongside apatite-wollastonite (used as comparison material), as potential biomaterials for bone tissue repair and regeneration. Glass frits of all the formulations were processed to have particle sizes under 53 μm, with their morphology and dimensions subsequently investigated by scanning electron microscopy (SEM). In order to establish the nature of the raw glass powders, X-ray diffraction (XRD) analysis was also performed. The sintering ability of the novel materials was determined by using hot stage microscopy (HSM). Ionic release potential was assessed by inductively coupled plasma optical emission spectroscopy (ICP-OES). Finally, the cytotoxic effect of the novel glass powders was evaluated for different glass concentrations via a colorimetric assay, on which basis three formulations are considered promising biomaterials.
... Worldwide many researchers have used the SiO 2 -Na 2 O-CaO-P 2 O 5 system as a template for developing new silica-based compositions [7]. Subsequently, many formulations in the phosphate and borate-based system have been also designed to overcome the Bioglass® and silicatebased glass limitations [8][9][10][11], and thus to meet the set of requirements that are both crucial and necessary for optimised tissue-engineered substitutes [12]. ...
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Article
Eight novel silicate, phosphate and borate glass compositions (coded as NCLx, where x = 1 to 8), containing different oxides (i.e. MgO, MnO2, Al2O3, CaF2, Fe2O3, ZnO, CuO, Cr2O3) were designed and evaluated alongside apatite-wollastonite (used as comparison material), as potential biomaterials for bone tissue repair and regeneration. Glass frits of all the formulations were processed to have particle sizes under 53 μm, with their morphology and dimensions subsequently investigated by scanning electron microscopy (SEM). In order to establish the nature of the raw glass powders, X-ray diffraction (XRD) analysis was also performed. The sintering ability of the novel materials was determined by using hot stage microscopy. Ionic release potential was assessed by inductively coupled plasma optical emission spectroscopy (ICP-OES). Finally, the cytotoxic effect of the novel glass powders was evaluated for different glass concentrations via a colorimetric assay, on which basis three formulations are considered promising biomaterials.
... Partial replacement of Na 2 O and CaO with K 2 O and MgO, respectively, was the most common strategy to design and adjust the TEC of the glass in a controlled way [14]. B 2 O 3 can be also added to the glass formulation to decrease the TEC, although borosilicate glasses show a higher tendency towards dissolution in aqueous media (including biological fluids) compared to silicate materials [17]. Using multiple glass layers of different compositions has been also proposed to achieve a good compromise among thermal behaviour, optimal dissolution rate and osteointegration [14]. ...
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Article
Bioactive glasses, invented by Prof. Larry L. Hench in the late 1960s, have revolutionized the field of biomaterials as they were shown to tightly bond to both hard and soft living tissues and to stimulate cells towards a path of regeneration and self-repair. However, due to their relatively poor mechanical properties (brittleness, low bending strength and fracture toughness), they are generally unsuitable for load-bearing applications. On the other hand, bioactive glasses have been successfully applied as coatings on the surface of stronger/tougher substrates to combine adequate mechanical properties with high bioactivity and, in some cases, additional extrafunctionalities (e.g. antibacterial properties, drug release). After giving a short overview of the main issues concerning the fabrication of glass coatings, this review provides a state-of-the-art picture in the field and specifically discusses the development of bioactive and hierarchical coatings on 3D porous scaffolds, joint prostheses, metallic substrates (e.g. wires or nails) for orthopedic fixation, polymeric meshes and sutures for wound healing, ocular implants and percutaneous devices.
... Bioactive glass ceramics have an important place in dental healthcare [1][2][3]. The glass-ceramics containing apatite [Ca 10 (PO 4 )6(O,F 2 )] and wollastonite [CaO·SiO 2 ] crystals as the predominant phases have been utilized either in powder form as bone filler or in bulk in prosthetic applications. ...
... Bioactive glass ceramics have an important place in dental healthcare [1][2][3]. The glass-ceramics containing apatite [Ca 10 (PO 4 )6(O,F 2 )] and wollastonite [CaO·SiO 2 ] crystals as the predominant phases have been utilized either in powder form as bone filler or in bulk in prosthetic applications. ...
Article
In this study, the contact area between the glass ceramic containing apatite [Ca10(PO4)6(O,F2)] and wollastonite [CaO·SiO2] crystals (A-W glass ceramic) and feldspathic dental porcelain was characterized using scanning electron microscope and energy dispersive spectroscopy. Alumina-added A–W glass ceramics were prepared by sintering glass compacts in the MgO-CaO-SiO2-P2O5-Al2O3 system at 1100 °C. Commercially available dental porcelains for alumina frameworks were applied on the A-W glass ceramic specimen by brushing and carving, and then fired at 960 °C using an electrically heated vacuum-furnace. Results revealed that veneering of feldspathic dental porcelain on alumina-added A-W glass ceramic is possible by an interaction betwen them, with which a diffusion process involving i) seperation of the phases forming the alumina-added A-W glass ceramic, ii) chemical diffusion of elements between alumina-added A-W glass ceramic and feldspathic dental porcelain, and iii) formation of an interface layer, is taking place. The system studied has interfacial characteristics similar to the commercially available dental materials currently used in restorative dentistry. Hence, it may be further processed for potential clinical applications.
... Kumar et al. [19] choose the mechano-chemical synthesis for the obtaining of leucite based glass-ceramic, which was further integrated in a bioactive dental veneering composite. Baino et al. [20] focused on the development of a three-layer system comprising a ceramic substrate, a glass derived trabecular coating and a glass-ceramic interlayer that joins the other two elements together for use in prosthetic applications. ...
Article
Starting from SiO2–CaO–P2O5–ZnO–CaF2 oxide system, vitroceramic materials were obtained by employing the sol-gel approach, followed by thermal treatment in order to provide, in a controlled manner, the nucleation and growth of crystalline phases in the parent glassy matrix. Thermal analysis, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, transmission electron microscopy, selected area electron diffraction and Fourier transformed infrared spectroscopy were employed for the characterization of the resulting samples. The sintered vitroceramics present calcium silicates as crystallized nano-domains and a porosity that decreases with the enhancement of the processing temperature. The assessment of the biological properties was carried out in vitro by simulated body fluid immersion for 14 days, associated with a detailed analysis of the apatitic layer formed on the surface.
Article
Thermal spraying of bioglasses offers the opportunity to produce coatings for different biomedical applications. The resorption of the coatings can be adjusted by tailoring the chemical composition of the glass and the coating microstructure. This thesis describes the production of novel bioactive and bioresorbable glass coatings for biomedical applications via an emerging suspension high velocity-oxy fuel (SHVOF) thermal spray. Bioglass® (45S5) was sprayed at the flame power of 90, 75, 50 and 25 kW by varying fuel (hydrogen) and oxygen flow rates. No coating was obtained at the flame power of 90 kW, and thin coating (< 10 µm) was obtained at 25 kW. Thick (25 ± 3 µm) and uniform coatings were obtained at the flame powers of 50 and 75 kW. The 50 kW coating was 16 ± 2 % porous, while the 75 kW coating was 10 ± 1 % porous. The bioactivity tests of the coatings showed that no hydroxyapatite (HA) was deposited on the surface of 25 kW coating even after seven days of immersion in simulated body fluid (SBF). Whilst, the coatings produced at 50 and 75 kW revealed HA deposition after three days. EDX analysis of the cross-section of the coated samples showed that the 50 kW initial coating thickness reduced from 25 µm to 6 µm after immersion in SBF for 7 days, which means that this microstructure was highly reactive towards SBF and hence behaved like a resorbable coating. Coatings from two bioactive glasses, namely ICIE16 (48.0 % SiO2, 33.0 % CaO, 6.6 % Na2O, 2.4 % P2O5 and 10.0 % K2O, in wt %.) and 13-93 (53.0 % SiO2, 6.0 % Na2O, 20.0 % CaO, 12.0 % K2O, 5.0 % MgO and 4.0 % P2O5, in wt %) were successfully produced at the flame powers of 50 and 75 kW. For both formulations, thick, porous and less hard coatings were obtained at 50 kW, whilst harder, dense and less thick coatings were obtained at 75 kW. ICIE16 coatings showed more dissolution in SBF than the 13-93 coatings. Moreover, in-vitro cell tests, using MG63 cells, showed good cell attachment and proliferation on the surfaces of the coating, revealing good cytocompatibility. Resorbable phosphate based glass (PBG), P-40 (40.0 % P2O5, 16.0 % CaO, 24.0 % MgO, 20.0 % Na2O in mol %) was sprayed at 50 and 75 kW flame power. The 75 kW coating was thinner and rougher than the 50 kW coating; both coatings presented globules on the surface. The Raman analysis of the P-40 coatings suggested that the structure of the glass had changed as the concentration of Q2 (2 bridging oxygen)species has been decreased. Whilst, Q1 (1 bridging oxygen) concentration has been increased and Q0 (0 bridging oxygen) species has been formed. Due to these structural alterations, these coatings showed less ion release and mass degradation than those reported in the literature for P-40 thin films and bulk glass. Ga2O3 doped Bioglass® was manufactured for antimicrobial applications and deposited at 50 kW. Moreover, Ga2O3 and Bioglass® suspensions were co-deposited via a hybrid nozzle at 50 kW to mix them in the flame. Both coatings showed bioactivity as HA was deposited on the surfaces of these coatings after immersion in SBF for 3 days. In summary, SHVOF thermal spraying has been proven to be an effective and versatile technique to deposit different bioglasses, maintaining their amorphous tetrahedral structure and composition.
Article
From long ago, orthopedists and physicians are trying to deal with bone diseases and disorders, while today, in the regenerative medicine field, bone scaffolds are being in attendance. Although there were common methods for fabricating bone scaffolds, such as foam casting and gas foaming, additive manufacturing (AM) techniques have been considered for producing bone scaffolds due to some appealing features such as creating a hierarchical structure, regular and controlled porosity, and designing of the complicated structures. AM techniques are divided into three categories, including extrusion-based, powder-based, and vat polymerization (light-based) techniques. Among the AM methods, the robocasting technique as an extrusion-based method is highly regarded for designing high-strength scaffolds for bone tissue regeneration owing to special features, for instance, a low-volume binder and the ability to print all types of ceramic materials as well as metals and polymers. This study discusses the robocasting method, as well as the essential parameters that are involved in 3D printing of the ideal scaffold with this method, such as the material, the structure of the robotic device, the printing parameters, the properties of the ideal paste or ink, the role of binder and its types in robocasting, and the rheological properties required in robocasting method. Also, future prospects and clinical applications of this technique were reviewed.
Chapter
Following the general increase of population and industrial development, the management of resources through use of secondary source of raw materials, recycling and energy recovery from waste products are growing in importance. There are many challenges associated with each approach in which waste treatment and handling its by-products are among the most environmentally concerned matters. This chapter is divided into two main parts for two types of waste management: municipal solid waste management, and wastewater management. In the first part, management of municipal solid waste, incineration as a tool for energy recovery and its hazardous by-products fly ash and bottom ash are introduced. It has shown that vitrification of these ashes could open lots of potential for their utilization in various products such as cement and clinker substitution, or preparation of foam glass–ceramics as construction materials. In this chapter, a guide to successfully vitrify fly ash is also introduced and discussed. The second part of this chapter is dedicated to wastewater management, focusing on the potential use of rice-husk, an agricultural by-product to be utilized as an adsorbent for removal of heavy metals from wastewater. The final heavy-metal containing rice husk introduces new environmental concerns prior to landfill, and we have shown that vitrification has the potential to safely encapsulate this material and even give the opportunity to prepare foam glass–ceramics after its vitrification.
Chapter
The invention of bioactive glasses has undoubtedly represented an important watershed in the history of biomedicine, innovatively revolutionizing the key concept of biomaterials. Although 50 years have passed since the first bioactive glass (45S5 Bioglass®), these materials still continue to inspire numerous generations of researchers all over the world, attracted by the promise of numerous possible fields of investigations given by the versatility of glass manufacturing and processing strategies. This allows obtaining final clinical products that are incredibly diverse in terms of chemical characteristics, shape and texture and, therefore, adaptable to different therapeutic needs. The possibility to tune textural properties and degradation rates, perform high-temperature sintering processes without or minimally altering the original properties of the glass, as well as the facile introduction of therapeutically active ions within the composition and the easy surface functionalization led, over year, to the development of multiple pruducts to be used in various clinical fields, including the regeneration of both hard and soft tissues, bacterial/viral infection treatments and development of antitumoral strategies. This chapter opens a wide window on the world of bioactive glasses, starting with the description of their peculiar chemical properties, discussed in relation to the most commonly used manufacturing processes to obtain glass monoliths or particles. Then, an overview on the most common applications of BG-based products will be provided, paying particular attention to porous scaffolds for bone tissue engineering, bioactive coatings, antibacterial glasses and surface functionalization. In conclusion, a comprehensive overview on clinical applications updated to the state of the art will be provided.
Chapter
Ceramic is associated to clay because earliest ceramic articles were made from naturally occurring materials such as clay minerals. Clays and many of the same raw materials are still serve as the main constituents of traditional ceramics that in broad sense encompass heavy clay products, construction materials, whitewares, refractories, glasses, etc. The aim of this chapter is to provide the basic information about the key technological operations and advances in production of structural clay products, wall and floor tiles, vitreous china sanitaryware, stoneware, majolica pottery and porcelain that would be useful to understand the world of these materials.
Chapter
Glass has been a versatile and fascinating material since the early stages of civilization. The aesthetic and functional properties of glasses are mainly dictated by the composition, which in most cases is a mixture of inorganic oxides and can be properly designed according to the end use. Glass–ceramics are polycrystalline materials produced by the controlled crystallization of certain parent glasses and contain one or more crystalline phases embedded in a residual amorphous matrix. The distinct chemical nature and microstructural features of these phases have led to various combinations of properties and applications in many industrial, medical and high-tech fields. This chapter introduces the reader into the “mystery of glass”, providing a picture of the structural theories, formation criteria and main processing methods for glass and glass–ceramic products with focus on a selected set of silicate materials..
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Advancements in technology allow for longer lifespan, creating the need for improved medical devices, especially in orthopedics. Using technologies like additive manufacturing (AM), it is possible to achieve a high degree of personalization, namely patient-specific implants with complex shapes and controlled porous structures. This process not only foments the creativity, but it also promotes the research of new biomaterials, and the optimisation of existing processes and techniques. During my PhD studies, I aimed to exploit AM for the development of novel materials and devices within bone regenerative medicine. I have investigated the use of Apatite-Wollastonite (AW), a bioactive glass-ceramic, as feedstock for AM techniques. From doping of AW powders with alumina to the use of the AW precursor glass as a filler for polymer-ceramic biocomposites, the goal was always to obtain a device able to improve osseointegration. A material like AW can be easily tuned, allowing for a high degree of freedom composition-wise. Two AM techniques were applied, binder jetting and fused filament fabrication, to create a load bearing device and scaffolds for critical-size defects, respectively. The choice of the developed materials and techniques envisioned the fast translation into an industrial context, and their easy commercialization.
Article
In this work we investigated the sintering behaviour of apatite-wollastonite (AW) glass-ceramic powders with the presence of alumina, firstly detected as a potentially useful surface contaminant derived from the ball milling of the powder, and then as a dopant in the glass formulation. All powders were benchmarked against AW without alumina. A small percentage of contamination (0.14 wt%) showed to delay the melting of material, and lower densification derived from a lower ability to crystallize and higher stability in the glassy states. The doped AW revealed that an increase in alumina favoured the formation of a glassy phase, increasing the degree of necking and the development of crystals. In conclusion, the introduction of alumina improves the AW glass-ceramic processability when content and process parameters are optimized.
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This work evaluates the impact of boron incorporation into bioactive glasses on their biokinetic, mechanic and structural properties. B2O3 doped (0.5-15 mol%) ordered mesoporous bioactive glasses (MBG) with the composition 80% SiO2 - 15% CaO - 5% P2O5 were synthesized via a sol-gel based evaporation-induced self-assembly process using the block-copolymer P123 as structure directing agent and characterized by biokinetic, mechanical and structural investigations. Nitrogen physisorption isotherms and electron microscopy indicate no detrimental effect of B2O3 on the ordered hexagonal pore structure. Boron incorporation increases both bulk modulus and hardness of the glasses. In-vitro bioactivity tests reveal rapid initial release of Ca2+ and PO43- ions, followed by formation of hydroxyapatite carbonate within a few hours. Contrary to the tight incorporation of Al in Al-doped MBGs, the rapid release of borate species into simulated-body-fluid suggests loosely bound species localized at the internal surfaces of the mesopores. 29Si, 11B, 31P, and 1H solid state NMR spectroscopy reveal that the majority of the borate is present as anionic BO4/2- species. The need for charge compensation leads to an increase in average degree of polymerization of the phosphate species for high boron contents. 11B{31P} rotational echo double resonance NMR results reveal the absence of B-O-P linkages. This structural model explains the rapid release of borate and the enhanced dissolution kinetics of the Ca2+ and phosphate species.
Article
Nitrifying bacteria immobilized on Fe2O3‐CaO‐SiO2 porous glass‐ceramics have extensive application prospects for wastewater treatment. To study the effect of the pore structure on the immobilization, Fe2O3‐CaO‐SiO2 porous glass‐ceramics with different porosities and pore sizes were prepared by sintering and the addition of pore‐forming agent. The pore size and apparent porosity can be controlled by the pore‐forming agent content and their sizes. Appropriate amount of the pore‐forming agent can promote the apparent porosity and increase the amount of immobilized nitrifying bacteria. The excess of the pore‐forming agent can cause the formation of the new crystalline phases and reduce the amount of immobilized nitrifying bacteria. In this study, we demonstrate that Fe2O3‐CaO‐SiO2 porous glass‐ceramics with 30% pore‐forming agent exhibit a moderate apparent porosity and good immobilization. This combination has good application prospects in the field of ammonia treatment in wastewater. This article is protected by copyright. All rights reserved.
Article
Considering that the structure of scaffold determines its functionality, in this study biphasic calcium phosphate (BCP) scaffold with highly interconnected macroporous structure was firstly fabricated by a polymeric sponge replication method, in which a ethanol solution (25 vol.%) was use for preparation of the slurry and a varying slurry viscosity during multiple impregnations was adopted. Then, the surface coating consisting of nano-hydroxyapatite (nHA) particles was formed by a dip coating technology, i.e. immersing the porous scaffold into the nHA slurry (20 mg/mL) and sintering it at 650 °C. Preliminary in vitro experiments showed that compared to BCP one, nHA-coated BCP scaffold could increase protein adsorption, form more complex bone-like apatite, and promote cell adhesion and proliferation, indicating that nHA-coated BCP scaffold exhibited superior biocompatibility and bioactivity. It might be attributed to its surface nanostructure and abundant nano- to micro- scale pores (< 10 μm). This nHA-coated BCP scaffold with both trabecular framework and surface nanoscale topography holds great promise in serving as bone graft for the orthopedic application.
Article
A lithium substituted 58 S bioactive glass (BG) containing from 0 to 10 mol% Li2O was synthesized through the sol-gel technique and the effect of Lithium substitutions on in vitro hydroxycarbonate apatite formation, osteoblast-like cell responses and antibacterial efficiency was studied. Structural and morphological evaluation using X-ray diffraction analysis, Fourier transform infrared spectroscopy, scanning electron microscopy revealed that 58 S BG with 5 mol% Li2O (BG-5) had no significant effect on the formation rate of crystalline hydroxycarbonate apatite however 58 S BG with 10 mol% Li2O lowered the bioactivity of the BG. The lower bioactivity of BG-10 was associated with a lower rate of Si and Ca ion release into the simulated body fluid. The 3-(4,5dimethylthiazol-2-yl)−2,5-diphenyltetrazolium bromide (MTT) assay and alkaline phosphatase (ALP) assessment methods revealed that the presence of Li had a stimulating influence on increasing of both proliferation and differentiation of MC3T3-E1 cells. A qualitative assessment of cell viability with Live/Dead technique and visualization of the morphology of actin fibers and nuclei of MC3T3 cells treated with Li-BGs with DAPI/Actin staining techniques showed that addition of Li resulted in an increase in the mean number of DAPI-labeled nuclei which was in reasonable agreement with MTT test. The Li substituted BGs exhibited a potential antibacterial effect against methicillin-resistant Staphylococcus aureus bacteria (MRSA). Results suggest that sample BG-5 is a good candidate for bone tissue engineering with optimal cell proliferation and ALP activity, good bioactivity and significant high antibacterial potential against MRSA.
Article
Bioactive glasses and related bioactive glass-ceramics have been used for over three decades in biomedical applications such as bulk, particulate, or coatings materials. More recently, highly porous bioactive glass-ceramic scaffolds for bone-Tissue engineering have also been developed from selected compositions of bioactive glasses. Current bioactive glass-ceramic scaffolds are characterized by an open porous network, high bioactivity, and mechanical properties similar to those of trabecular bone. This article reviews the latest achievements in the development of porous bioactive glass-ceramics intended for bone-Tissue engineering applications, highlighting the fabrication technologies and scaffold properties. Improvements in the mechanical properties of bioactive glass-ceramic scaffolds exhibiting high bioactivity have been achieved by different approaches in the last 10 years. Relevant long-Term in vivo studies are required to confirm the suitability of such bioactive glass-ceramic scaffolds in clinical applications.
Article
To eliminate the negative effects of surface flaws and subsurface damage of glass–ceramics on clinical effectiveness, crack propagation and the material removal mechanism of glass–ceramics were studied by single and double scratch experiments conducted using an ultra-precision machine. A self-manufactured pyramid shaped single-grit tool with a small tip radius was used as the scratch tool. The surface and subsurface crack propagations and interactions, surface morphology and material removal mechanism were investigated. The experimental results showed that the propagation of lateral cracks to the surface and the interaction between the lateral cracks and radial cracks are the two main types of material peeling, and the increase of the scratch depth increases the propagation angle of the radial cracks and the interaction between the cracks. In the case of a double scratch, the propagation of lateral cracks and radial cracks between paired scratches results in material peeling. The interaction between adjacent scratches depends on the scratch depth and separation distance. There is a critical separation distance where the normalized material removal volume reaches its peak. These findings can help reduce surface flaws and subsurface damage induced by the grinding process and improve the clinical effectiveness of glass–ceramics used as biological substitute and repair materials.
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Article
Three novel borosilicate bioactive glasses (BBGs) of general formula of 0.05Na2O·0.35x·0.20B2O3·0.40SiO2 (molar ratio, where x = MgO or CaO or SrO) were prepared and used to investigate the effect of crystallization on their properties including cytotoxicity. The three postmelt compositions were determined using X-ray fluorescence spectroscopy, and crystallization events were studied using differential thermal analysis and X-ray diffraction. This information was used to determine heat treatments to prepare glass-ceramics by controlled crystallization. X-ray diffraction analysis and Fourier transform infrared spectroscopy showed that, after higher heat treatment temperatures (800-900 °C), borosilicate bioactive glass-ceramics (BBGCs) contained mainly borate and silicate crystalline phases. Specifically, BBG-Mg, BBG-Ca, and BBG-Sr glass-ceramics detected the presence of magnesium silicate-Mg2(SiO3)2 and magnesium borate-Mg2B2O5; wollastonite-2M-CaSiO3 and calcium borate-Ca(BO2)2; and strontium silicate-SrSiO3 and strontium borate-Sr2B2O5, respectively. In vitro cytotoxicity tests were performed using the mouse fibroblast cell line (L929). Glass and glass ceramic at concentrations lower than 50 mg/mL did not exhibit any level of cytotoxicity when compared with the control. However, quantitative evaluation indicated that greater cell growth occurred in the presence of materials with crystalline phases. Control of BBGs crystallization may therefore be used to influence the biocompatibility of these glass-ceramic systems.
Article
The main purpose of this study consists in investigating the effects of h-BN addition on the sinterability of β-CaSiO3 (β-CS) bioceramics. β-CS bioceramics with different contents of h-BN were prepared at the sintering temperature ranging from 800 °C to 1100 °C. The results showed that h-BN can be successfully used as sintering additive by being oxidized to form low melting point B2O3 related glassy phase and enhanced the flexural strength by the formation of rod-like β-CS grains. β-CS bioceramics with 1 wt.% h-BN sintered at 1000 °C revealed flexural strength and fracture toughness of 182.2 MPa and 2.4 MPa·m1/2 respectively, which were much higher than that of pure β-CS bioceramics (30.2 MPa, 0.53 MPa·m1/2) fabricated in the same processing condition.
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Over the last two decades, the philosophy behind an optimal fixation of orthopaedic implants progressively evolved towards "bone-conservative" solutions and, accordingly, the researchers' attention moved from simple mechanical fixation of the prosthesis to host bone by using screws or acrylic cement to new strategies based on a physico-chemical bond (surface modification) in order to minimize bone resection/loss and maximize tissue-implant integration. This research work explores the feasibility of a novel bioceramic single-piece acetabular cup for hip joint prosthesis that can be anchored to the patient's pelvic bone by means of a bone-like trabecular coating (scaffold) able to promote implant osteointegration.
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In this work, the coating of 3-D foam-like glass-ceramic scaffolds with a bioactive mesoporous glass (MBG) was investigated. The starting scaffolds, based on a non-commercial silicate glass, were fabricated by the polymer sponge replica technique followed by sintering; then, electrophoretic deposition (EPD) was applied to deposit a MBG layer on the scaffold struts. EPD was also compared with other techniques (dipping and direct in situ gelation) and it was shown to lead to the most promising results. The scaffold pore structure was maintained after the MBG coating by EPD, as assessed by SEM and micro-CT. In vitro bioactivity of the scaffolds was assessed by immersion in simulated body fluid and subsequent evaluation of hydroxyapatite (HA) formation. The deposition of a MBG coating can be a smart strategy to impart bioactive properties to the scaffold, allowing the formation of nano-structured HA agglomerates within 48 h from immersion, which does not occur on uncoated scaffold surfaces. The mechanical properties of the scaffold do not vary after the EPD (compressive strength ~19 MPa, fracture energy ~1.2 × 10(6) J m(-3)) and suggest the suitability of the prepared highly bioactive constructs as bone tissue engineering implants for load-bearing applications.
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This review focuses on recent advances in the development and use of bioactive glass for tissue engineering applications. Despite its inherent brittleness, bioactive glass has several appealing characteristics as a scaffold material for bone tissue engineering. New bioactive glasses based on borate and borosilicate compositions have shown the ability to enhance new bone formation when compared to silicate bioactive glass. Borate-based bioactive glasses also have controllable degradation rates, so the degradation of the bioactive glass implant can be more closely matched to the rate of new bone formation. Bioactive glasses can be doped with trace quantities of elements such as Cu, Zn and Sr, which are known to be beneficial for healthy bone growth. In addition to the new bioactive glasses, recent advances in biomaterials processing have resulted in the creation of scaffold architectures with a range of mechanical properties suitable for the substitution of loaded as well as non-loaded bone. While bioactive glass has been extensively investigated for bone repair, there has been relatively little research on the application of bioactive glass to the repair of soft tissues. However, recent work has shown the ability of bioactive glass to promote angiogenesis, which is critical to numerous applications in tissue regeneration, such as neovascularization for bone regeneration and the healing of soft tissue wounds. Bioactive glass has also been shown to enhance neocartilage formation during in vitro culture of chondrocyte-seeded hydrogels, and to serve as a subchondral substrate for tissue-engineered osteochondral constructs. Methods used to manipulate the structure and performance of bioactive glass in these tissue engineering applications are analyzed.
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Traditionally, bioactive glasses have been used to fill and restore bone defects. More recently, this category of biomaterials has become an emerging research field for bone tissue engineering applications. Here, we review and discuss current knowledge on porous bone tissue engineering scaffolds on the basis of melt-derived bioactive silicate glass compositions and relevant composite structures. Starting with an excerpt on the history of bioactive glasses, as well as on fundamental requirements for bone tissue engineering scaffolds, a detailed overview on recent developments of bioactive glass and glass-ceramic scaffolds will be given, including a summary of common fabrication methods and a discussion on the microstructural-mechanical properties of scaffolds in relation to human bone (structure-property and structure-function relationship). In addition, ion release effects of bioactive glasses concerning osteogenic and angiogenic responses are addressed. Finally, areas of future research are highlighted in this review.
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This work explores the feasibility of glass-derived coatings (SiO2-CaO-Na2O-Al2O3 system) on bioceramic devices of complex shape by a layer-wise slurry deposition using an airbrush spray gun. Specifically, glass-ceramic coatings with thickness in the 50-500 μm range were prepared on alumina curved substrates by airbrush spraying of glass-based aqueous suspensions followed by sintering. Investigations by scanning electron microscopy and micro-computed tomography revealed that, under appropriate optimization of slurry composition and spraying cycles, this technique is suitable to manufacture homogeneous and continuous coatings on model curved ceramic surfaces. It was observed that neither cracking nor delamination occurred at the interface between coating and substrate. Ad-hoc tensile tests were carried out by properly adapting the relevant ASTM standard to the specific case (curved geometry); the coating adhesion strength was found adequate (about 25 MPa) for biomedical applications. A simple model describing the relationship between coating thickness and number of spraying cycles was also developed and proposed as a useful tool to improve the design and manufacturing of bioceramic coatings. © 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Article
The tensile strength test of highly porous ceramic foams has been developed and first results have been obtained on bioactive glass foams. The tested material was a 45S5 Bioglass (R) derived foam-like scaffold intended for use in bone tissue engineering which was manufactured by Bioglass (R) slurry coating of polyurethane foam and subsequent sintering. The Bioglass (R) foam structure was investigated in two states: uncoated (as fabricated) and with a PDLLA polymer coating. The tensile testing procedure is based on fixation of the foam into aluminium pots by a suitable adhesive. Tensile test samples having cross-section of 10 x 10 mm(2) and a length of 30 mm were used for the experiments. Basic fractographic analysis was applied to get relevant information about specimens' behaviour during tensile loading. In Bioglass (R) based scaffolds, the presence of PDLLA coating led to a significant increase of the fracture strength, which is attributed to the interaction of the polymer phase with propagating cracks, e.g. enabling a crack bridging mechanism to take place.
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The development of reliable, synthetic scaffolds to repair large defects in load-bearing bones is one of the key challenges of regenerative medicine of hard tissues. This study addresses the mechanical properties of experimental glass–ceramic scaffolds fabricated by sponge replication and exhibiting a bone-like 3-D trabecular architecture, as assessed by micro-computed tomography investigations. The scaffolds have a strength of 18 MPa, an elastic modulus around 380 MPa, a Weibull modulus of 4 and a fracture energy of 544 kJ m−3 when tested in compression. Such results were compared with and found similar or even superior to those reported in the literature for bioceramic scaffolds and human cancellous bone. These key mechanical data, together with the peculiar foam-like porous architecture, indicate the great potential of this type of scaffolds for use in load-bearing bone tissue engineering applications.
Article
The sintering process of 45S5 Bioglass (R) powder (mean particle size < 5 mu m) was investigated by using different thermal analysis methods. Heating microscopy and conventional dilatometry techniques showed that bioactive glass sinters in two major steps: a short stage in the temperature range 500-600 degrees C and a longer stage in the range 850-1100 degrees C. The optimal sintering temperature and time were found to be 1050 degrees C and 140 min, respectively. Differential thermal analysis (DTA) showed that Bioglass (R) crystallises at temperatures between 600 and 750 degrees C. The characteristic crystalline phases were identified by Fourier Transformed Infrared Spectroscopy (FTIR), Transmission Electron Microscopy (TEM) and X-Ray Diffraction (XRD). The crystallisation kinetics was studied by DTA, using a non-isothermal method. The Kissinger plot for Bioglass (R) powder heated at different heating rates between 5 and 30 degrees C/min yielded an activation energy of 316 kJ/mol. The average value of Avrami parameter determined using the Augis-Bennett method was 0.95 +/- 0.10, confirming a surface crystallisation mechanism. After sintering at 1050 degrees C for 140 min, the main crystalline phase was found to be Na(2)Ca(2)Si(3)O(9). The results of this work are useful for the design of the sintering/crystallisation heat treatment of Bioglass (R) powder which is used for fabricating tissue engineering scaffolds with varying degree of bioactivity.
Article
A new approach based on the concepts of quantized fracture mechanics (QFM) is presented and discussed in this paper to estimate the bonding strength of trabecular-like coatings, i.e. glass-ceramic scaffolds mimicking the architecture of cancellous bone, to ceramic substrates. The innovative application of glass-derived scaffolds as trabecular-like coatings is proposed in order to enhance the osteointegration of prosthetic ceramic devices. The scaffolds, prepared by polymeric sponge replication, are joined to alumina substrates by a dense glass-ceramic coating (interlayer) and the so-obtained 3-layer constructs are investigated from micro-structural, morphological and mechanical viewpoints. In particular, the fracture strengths of three different crack propagation modes, i.e. glass-derived scaffold fracture, interface delamination or mixed fracture, are predicted in agreement with those of experimental mechanical tests. The approach proposed in this work could have interesting applications towards an ever more rational design of bone tissue engineering biomaterials and coatings, in view of the optimization of their mechanical properties for making them actually suitable for clinical applications.
Article
Ceramics used for the repair and re- construction of diseased or damaged parts of the musculo-skeletal sys- tem, termed bioceramics, may be bio- inert (alumina, zirconia), resorbable (tricalcium phosphate), bioactive (hy- droxyapatite, bioactive glasses, and glass-ceramics), or porous for tissue ingrowth (hydroxyapatite-coated met- als, alumina). Applications include re- placements for hips, knees, teeth, tendons, and ligaments and repair for periodontal disease, maxillofacial re- construction, augmentation and stabi- lization of the jaw bone, spinal fusion, and bone fillers after tumor surgery. Carbon coatings are thromboresistant and are used for prosthetic heart valves. The mechanisms of tissue bonding to bioactive ceramics are be- ginning to be understood, which can result in the molecular design of bio- ceramics for interfacial bonding with hard and soft tissues. Composites are being developed with high toughness and elastic modulus match with bone. Therapeutic treatment of cancer has been achieved by localized delivery of radioactive isotopes via glass beads. Development of standard test methods for prediction of long-term (20-year)
Article
There is a need to develop synthetic scaffolds to repair large defects in load-bearing bones. Bioactive glasses have attractive properties as a scaffold material for bone repair, but data on their mechanical properties are limited. The objective of the present study was to comprehensively evaluate the mechanical properties of strong porous scaffolds of silicate 13-93 bioactive glass fabricated by robocasting. As-fabricated scaffolds with a grid-like microstructure (porosity 47%, filament diameter 330μm, pore width 300) were tested in compressive and flexural loading to determine their strength, elastic modulus, Weibull modulus, fatigue resistance, and fracture toughness. Scaffolds were also tested in compression after they were immersed in simulated body fluid (SBF) in vitro or implanted in a rat subcutaneous model in vivo. As fabricated the scaffolds had a strength of 86±9MPa, elastic modulus of 13±2GPa, and a Weibull modulus of 12 when tested in compression. In flexural loading the strength, elastic modulus, and Weibull modulus were 11±3MPa, 13±2GPa, and 6, respectively. In compression the as-fabricated scaffolds had a mean fatigue life of ∼106 cycles when tested in air at room temperature or in phosphate-buffered saline at 37°C under cyclic stresses of 1-10 or 2-20MPa. The compressive strength of the scaffolds decreased markedly during the first 2weeks of immersion in SBF or implantation in vivo, but more slowly thereafter. The brittle mechanical response of the scaffolds in vitro changed to an elasto-plastic response after implantation for longer than 2-4weeks in vivo. In addition to providing critically needed data for designing bioactive glass scaffolds the results are promising for the application of these strong porous scaffolds in loaded bone repair.
Article
Bioactive glasses, discovered by Hench and co-workers at the end of the 1960s, are among the most promising biomaterials for bone repair and reconstruction, mainly thanks to their high bioactivity index. Unfortunately, due to their brittleness and relatively poor mechanical properties, their clinical applications are limited to non-load bearing implants. However, bioactive glasses can be successfully employed as coatings on bioinert metallic substrates, in order to combine high bioactivity with mechanical strength. After a brief introduction to the main properties of biomaterials and bioactive glasses, the present paper provides an overview of the different approaches and available techniques to realise bioactive glass coatings, with a particular emphasis on thermal spray, which is nowadays one of the most popular coating procedures.
Article
Glass-ceramics in the systems RO–BaO–SiO2 (R = Mg, Zn) have good thermal properties for sealing materials on planar-type solid oxide fuel cells (SOFC) at high and intermediate temperatures. In this work, the glass forming regions in the two systems have been determined. Composition lines with different BaO/RO ratios have been defined varying the silica content. The dilatometric properties of the melted glasses (coefficient of thermal expansion, glass transition temperature and softening temperature) have been measured to identify the glasses that best fulfill the cell requirements, such as a thermal expansion coefficient in the range (8.5–12) × 10−6 K−1. Since the sealing process is carried out employing paste technology during the heating and working schedule of the cell, it is important to study the interaction between sintering and crystallization to make dense materials with an adequate microstructure. The sintering and crystallization kinetics have been characterized for some selected glass compositions by using hot-stage microscopy (HSM) and differential thermal analysis (DTA). A new parameter SC = TX − TMS which takes into account the onset crystallization temperature (TX), temperature of maximum shrinkage (TMS) is proposed as an empirical method to evaluate the ability of glass sintering of the studied compositions and indicate good materials for glass-ceramic SOFC products.
Article
Bioactive glasses are reported to be able to stimulate more bone regeneration than other bioactive ceramics but they lag behind other bioactive ceramics in terms of commercial success. Bioactive glass has not yet reached its potential but research activity is growing. This paper reviews the current state of the art, starting with current products and moving onto recent developments. Larry Hench's 45S5 Bioglass® was the first artificial material that was found to form a chemical bond with bone, launching the field of bioactive ceramics. In vivo studies have shown that bioactive glasses bond with bone more rapidly than other bioceramics, and in vitro studies indicate that their osteogenic properties are due to their dissolution products stimulating osteoprogenitor cells at the genetic level. However, calcium phosphates such as tricalcium phosphate and synthetic hydroxyapatite are more widely used in the clinic. Some of the reasons are commercial, but others are due to the scientific limitations of the original Bioglass 45S5. An example is that it is difficult to produce porous bioactive glass templates (scaffolds) for bone regeneration from Bioglass 45S5 because it crystallizes during sintering. Recently, this has been overcome by understanding how the glass composition can be tailored to prevent crystallization. The sintering problems can also be avoided by synthesizing sol-gel glass, where the silica network is assembled at room temperature. Process developments in foaming, solid freeform fabrication and nanofibre spinning have now allowed the production of porous bioactive glass scaffolds from both melt- and sol-gel-derived glasses. An ideal scaffold for bone regeneration would share load with bone. Bioceramics cannot do this when the bone defect is subjected to cyclic loads, as they are brittle. To overcome this, bioactive glass polymer hybrids are being synthesized that have the potential to be tough, with congruent degradation of the bioactive inorganic and the polymer components. Key to this is creating nanoscale interpenetrating networks, the organic and inorganic components of which have covalent coupling between them, which involves careful control of the chemistry of the sol-gel process. Bioactive nanoparticles can also now be synthesized and their fate tracked as they are internalized in cells. This paper reviews the main developments in the field of bioactive glass and its variants, covering the importance of control of hierarchical structure, synthesis, processing and cellular response in the quest for new regenerative synthetic bone grafts. The paper takes the reader from Hench's Bioglass 45S5 to new hybrid materials that have tailorable mechanical properties and degradation rates. Copyright © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Article
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
Article
Formation of a high-strength bioactive glass-ceramic in the system MgO-CaO-SiO2-P2O5 was investigated by observing the microstructure of the crystallized products. Crystallization of the parent glass in a bulk form led to the occurrence of large cracks in the crystallized product. This was attributed to the precipitation of fibrous-wollastonite crystals growing perpendicular to the outer surfaces of the glass after uniform precipitation of fine oxyapatite/fluoroapatite crystals. On the other hand, crystallization of the same glass in a powder compact led to the formation of a crack-free dense crystallized product due to uniform precipitation of both apatite and wollastonite fine crystals throughout the glass article. The uniform precipitation of the wollastonite crystals was attributed to the simultaneous formation of fine crystals in the individual glass particles.
Article
Sixteen glasses in the SiO2-Na2O-CaO-P2O5-Al2O3-B2O3 system were studied. The glasses were implanted in rabbit tibia. According to theirin vivo behaviour, they were divided into five groups. A phenomenological equation for thein vivo behaviour was developed. The solubility of the glasses was determinedin vitro as weight loss in Tris buffer solution. The tissue response is discussed in relation to the glass composition and the solubility. For bone-bonding glasses calcium phosphate formation takes place within a silica-gel at the glass surface. The gel must be sufficiently hydrated and flexible to allow calcium phosphate to build up. The results suggest that alumina can inhibit bone bonding by retarding the formation rate of a silica-rich layer, by stabilizing the silica structure enough to prevent calcium phosphate build-up within the layer, or by either disturbance of the bone mineralization or bone incompatibility of an alumina-containing calcium- and phosphorus-rich surface layer. The mechanism responsible for the lack of bone adherence is determined by the glass composition. Up to about 1.5 wt % Al2O3 can be included in the glass without destroying the bioactivity.
Article
A simple method is described that makes possible fast evaluation of glass-forming tendency on the basis of relative position of the recrystallization, transformation and melting temperatures. These temperatures are determined by means of DTA. One assumes that the glass-forming tendency is proportional to the thermal stability of glass. The glass-forming tendency is expressed numerically, thus enabling one to compare different kinds of glasses and the influence of various impurities. The validity of the model is experimentally verified on the CdAs2 and As2Te3 systems containing different admixtures.
Article
The aim of this work was the preparation and characterization of scaffolds with mechanical and functional properties able to regenerate bone. Porous scaffolds made of chitosan/gelatin (POL) blends containing different amounts of a bioactive glass (CEL2), as inorganic material stimulating biomineralization, were fabricated by freeze-drying. Foams with different compositions (CEL2/POL 0/100; 40/60; 70/30 wt %/wt) were prepared. Samples were crosslinked using genipin (GP) to improve mechanical strength and thermal stability. The scaffolds were characterized in terms of their stability in water, chemical structure, morphology, bioactivity, and mechanical behavior. Moreover, MG63 osteoblast-like cells and periosteal-derived stem cells were used to assess their biocompatibility. CEL2/POL samples showed interconnected pores having an average diameter ranging from 179 ± 5 μm for CEL2/POL 0/100 to 136 ± 5 μm for CEL2/POL 70/30. GP-crosslinking and the increase of CEL2 amount stabilized the composites to water solution (shown by swelling tests). In addition, the SBF soaking experiment showed a good bioactivity of the scaffold with 30 and 70 wt % CEL2. The compressive modulus increased by increasing CEL2 amount up to 2.1 ± 0.1 MPa for CEL2/POL 70/30. Dynamical mechanical analysis has evidenced that composite scaffolds at low frequencies showed an increase of storage and loss modulus with increasing frequency; furthermore, a drop of E' and E″ at 1 Hz was observed, and for higher frequencies both moduli increased again. Cells displayed a good ability to interact with the different tested scaffolds which did not modify cell metabolic activity at the analyzed points. MTT test proved only a slight difference between the two cytotypes analyzed.
Article
In this work, the use of foam-like glass-ceramic scaffolds as trabecular coatings on ceramic prosthetic devices to enhance implant osteointegration is proposed. The feasibility of this innovative device was explored in a simplified, flat geometry: glass-ceramic scaffolds, prepared by polymeric sponge replication and mimicking the trabecular architecture of cancellous bone, were joined to alumina square substrates by a dense glass coating (interlayer). The role played by different formulations of starting glasses was examined, with particular care to the effect on the mechanical properties and bioactivity of the final coating. Microindentations at the coating/substrate interface and tensile tests were performed to evaluate the bonding strength between the sample's components. In vitro bioactive behaviour was assessed by soaking in simulated body fluid and evaluating the apatite formation on the surface and inside the pores of the trabecular coating. The concepts disclosed in the present study can have a significant impact in the field of implantable devices, suggesting a valuable alternative to traditional, often invasive bone-prosthesis fixation.
Article
There have been a number of major advances made in the field of bioactive ceramics, glasses and glass ceramics during the past 30–40 years. From initial work on the development of materials that are tolerated in the physiological environment, emphasis has now shifted towards the use of ceramic materials that interact with bone tissue by forming a direct bond. It is now possible to choose, by compositional control, whether these materials are biologically stable once incorporated within the skeletal structure or whether they are resorbed over time. This paper reviews the ground-breaking work that was performed during the 1970s and 1980s in the field of bioceramics in the production and characterisation of bioactive and bioresorbable glasses, glass ceramics and calcium phosphates. The review then explores the influence of the original concepts and ideas on the more recent development of ceramic scaffolds, composites and coatings with enhanced bioactivity for bone tissue engineering.
Article
A fundamental issue for the restoration of bone defects according to a tissue engineering approach is the development of highly porous bioactive scaffolds. The polymer burning out method is widely employed to fabricate bioceramic scaffolds because of its versatility, simplicity and low cost. However, the resulting scaffolds may suffer low porosity and non-interconnected pores. In the present contribution a new fabrication method is presented. Thanks to a recently developed potassium-based bioactive glass, which has the peculiarity to be sintered at a relatively low temperature (i.e. ∼750 °C), it was possible to use sodium chloride particles as pore generating agents, which helped to maintain the shape of the struts during the entire sintering process. The salt particles can be easily removed by immersing the scaffold in water, giving place to a structure that combines high porosity (in the 70–80 vol.% range) with interconnected pores and an appreciable mechanical behaviour (Young's modulus in the 3.4–3.7 MPa range according to compression tests).
Article
As health care is improving, our life expectancy is increasing but as we get older we lose bone density due to osteoporosis. At present the treatment for severe cases of osteoporosis is the total hip replacement. This has been one of the most successful surgical procedures in the history of medicine, but it uses bio-inert materials to replace damaged bone. These materials cause further loss in bone density and eventually the replacement needs to be replaced. A patient that has a hip replacement at the age of 60 may need several revision operations by the time they reach ninety. For large done defects an alternative is transplantation, but there are limitations of a lack of donors and morbidity of the donor site. Both of these techniques are tissue replacement techniques. A shift in thinking is required from tissue replacement to the regeneration of tissues to their original state and function. One path to follow is the regeneration of bone using ceramic and glass scaffolds that mimic the structure of bone mineral, bond to bone and in some cases activate the genes within bone cells to stimulate new bone growth.
Article
Three bio-phosphate glass-specimens with and without Al2O3 addition were prepared in order to shed light on their bioactivity behavior towards the simulated body fluid biological solution (SBF). The results revealed that Al2O3 has significant effect on the ability of bio-glass to form the hydroxycarbonate apatite layer on its surface. That layer was detected by FTIR spectra, SEM micrographs and EDAX pattern. Also, the effect of Al2O3 on the mechanical properties was studied by measuring the hardness of the glass samples, which increased by Al2O3 addition. The thermal expansion coefficient was decreased by increasing the Al2O3 percent in the bio-glass samples.
Article
The objective of this work is to develop bioactive glass coatings for metallic orthopedic implants. A new family of glasses in the SiO2–Na2O–K2O–CaO–MgO–P2O5 system has been synthesized and characterized. The glass properties (thermal expansion, softening and transformation temperatures, density and hardness) are in line with the predictions of established empirical models. The optimized firing conditions to fabricate coatings on Ti-based and Co–Cr alloys have been determined and related to the glass properties and the interfacial reactions. Excellent adhesion to alloys has been achieved through the formation of 100–200 nm thick interfacial layers (Ti5Si3 on Ti-based alloys and CrOx on Co–Cr). Finally, glass coatings, approximately 100 μm thick, have been fabricated onto commercial Ti alloy-based dental implants.
Article
Fabrication of 3-D highly porous, bioactive, and mechanically competent scaffolds represents a significant challenge of bone tissue engineering. In this work, Bioglass®-derived glass-ceramic scaffolds actually fulfilling this complex set of requirements were successfully produced through the sponge replication method. Scaffold processing parameters and sintering treatment were carefully designed in order to obtain final porous bodies with pore content (porosity above 70 %vol), trabecular architecture and mechanical properties (compressive strength up to 3 MPa) analogous to those of the cancellous bone. Influence of the Bioglass® particles size on the structural and mechanical features of the sintered scaffolds was considered and discussed. Relationship between porosity and mechanical strength was investigated and modeled. Three-dimensional architecture, porosity, mechanical strength and in vitro bioactivity of the optimized Bioglass®-derived scaffolds were also compared to those of CEL2-based glass-ceramic scaffolds (CEL2 is an experimental bioactive glass originally developed by the authors at Politecnico di Torino) fabricated by the same processing technique, in an attempt at understanding the role of different bioactive glass composition on the major features of scaffolds prepared by the same method.
Article
Biomaterials used in regenerative medicine are often designed to act as 3D porous templates (scaffolds) able to support and promote the growth and repair of natural tissues. Some types of glasses have a great potential for making bone tissue engineering scaffolds, as they can bond to host bone, stimulate bone cells toward osteogenesis, and resorb at the same time as the bone is repaired. This review article highlights the evolution of glass-based scaffolds for bone tissue engineering; specifically, the features, limitations, and advantages of the different types of glass-derived scaffolds proposed in the literature (macroporous glass-ceramic, sol-gel glass, composite, graded, hybrid, and hierarchical implants) are critically examined, discussed, and compared. Future directions for the research are also suggested, highlighting the promise of multifunctional systems able to combine bone regeneration and drug release abilities, the increasing role of nondestructive advanced imaging techniques, such as X-ray microtomography, for scaffolds investigation and the potential of stem cells incorporation into scaffolds.
Article
Several inorganic materials such as special compositions of silicate glasses, glass-ceramics and calcium phosphates have been shown to be bioactive and resorbable and to exhibit appropriate mechanical properties which make them suitable for bone tissue engineering applications. However, the exact mechanism of interaction between the ionic dissolution products of such inorganic materials and human cells are not fully understood, which has prompted considerable research work in the biomaterials community during the last decade. This review comprehensively covers literature reports which have investigated specifically the effect of dissolution products of silicate bioactive glasses and glass-ceramics in relation to osteogenesis and angiogenesis. Particularly, recent advances made in fabricating dense biomaterials and scaffolds doped with trace elements (e.g. Zn, Sr, Mg, and Cu) and investigations on the effect of these elements on the scaffold biological performance are summarized and discussed in detail. Clearly, the biological response to artificial materials depends on many parameters such as chemical composition, topography, porosity and grain size. This review, however, focuses only on the ion release kinetics of the materials and the specific effect of the released ionic dissolution products on human cell behaviour, providing also a scope for future investigations and identifying specific research needs to advance the field. The biological performance of pure and doped silicate glasses, phosphate based glasses with novel specific compositions as well as several other silicate based compounds are discussed in detail. Cells investigated in the reviewed articles include human osteoblastic and osteoclastic cells as well as endothelial cells and stem cells.
Article
Glass-ceramics in the diopside (CaMgSi2O6)-fluorapatite (Ca5(PO4)3F)-wollastonite (CaSiO3) system are potential candidates for restorative dental and bone implant materials. The present study describes the influence of varying SiO2/CaO and CaF2/P2O5 molar ratio on the structure and thermal behavior of glass compositions in the CaO-MgO-SiO2-P2O5-Na2O-CaF2 system. The structural features and properties of the glasses were investigated by nuclear magnetic resonance (NMR), infrared spectroscopy, density measurements and dilatometry. Sintering and crystallization behavior of the glass powders were studied by hot-stage microscopy and differential thermal analysis, respectively. The microstructure and crystalline phase assemblage in the sintered glass powder compacts were studied under non-isothermal heating conditions at 825 °C. X-ray diffraction studies combined with the Rietveld-reference intensity ratio (R.I.R) method were employed to quantify the amount of amorphous and crystalline phases in the glass-ceramics, while scanning electron microscopy was used to shed some light on the microstructure of resultant glass-ceramics. An increase in CaO/SiO2 ratio degraded the sinterability of the glass powder compacts, resulting in the formation of akermanite as the major crystalline phase. On the other hand, an increase in P2O5/CaF2 ratio improved the sintering behavior of the glass-ceramics, while varying the amount of crystalline phases, i.e. diopside, fluorapatite and wollastonite.
Article
Bioactive glass is currently regarded as the most biocompatible material in the bone regeneration field because of its bioactivity, osteoconductivity and even osteoinductivity. In the present work porous glass-ceramic scaffolds, which were prepared from the 45S5 Bioglass by foaming with rice husks and sintering at 1050 degrees C for 1 h, have been developed. The produced scaffolds were characterized for their morphology, properties and bioactivity. Micrographs taken using a scanning electron microscope (SEM) were used for analysis of macropores, mesopores and micropores, respectively. The bioactivity of the porous glass-ceramic scaffolds was investigated using simulated body fluid (SBF) and characterized by SEM, energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). A great potential scaffold that provides sufficient mechanical support temporarily while maintaining bioactivity, and that can biodegrade at later stages is achievable with the developed 45S5 Bioglass-derived scaffolds.
Article
Data on the tensile and compressive properties of trabecular bone are needed to define input parameters and failure criteria for modeling total joint replacements. To help resolve differences in reports comparing tensile and compressive properties of trabecular bone, we have developed new methods, based on porous foam technology, for tensile testing of fresh/frozen trabecular bone specimens. Using bovine trabecular bone from an isotropic region from the proximal humerus as a model material, we measured ultimate strengths in tension and compression for two groups of 24 specimens each. The average ultimate strength in tension was 7.6 +/- 2.2 (95% C.I.) MPa and in compression was 12.4 +/- 3.2 MPa. This difference was statistically significant (p = 0.013) and was not related to density differences between the test groups (p = 0.28). Strength was related by a power-law function of the local apparent density, but, even accounting for density influences, isotropic bovine trabecular bone exhibits significantly lower strengths in tension than in compression.
Article
Evidence for the lack of toxicity of various bioglass formulations has been deduced from studies carried out, both in vivo and in vitro, in several different centers. Recent studies of the authors, described here, include testing of solid bioglass implants in the soft tissues of rats and rabbits for time periods of up to eight weeks. Two new techniques are described for the toxicological testing of particulate biomaterials. These tests, which involve rat peritoneal macrophages in culture and a mouse pulmonary biomaterial embolus model, indicate the biocompatibility of bioglass powders. Thus, the surface activity so critical in bone adhesion is without toxic effect in non-osseous tissues in contact with solid bioglass implants. Should wear occur and produce particulate bioglass, the material should be eliminated without consequence.
Article
The purpose of this study was to review the University of Florida's long-term results with Bioglass middle ear prostheses. Between April 1984 and November 1987, 37 patients were implanted with Bioglass prostheses (25 total and 12 partial ossicular replacements). Twenty-one patients had postoperative data of at least 24 months (range, 24 to 126 months; mean, 86 months; median, 100 months), and five patients had > 10 years' follow-up. In three cases, portions of fractured prostheses extruded, leaving an intact tympanic membrane. One patient with a total ossicular prosthesis was reexplored at 38 months for conductive hearing loss and found to have a prosthesis fracture (n = 1). There were no extrusions of intact prostheses, even in patients in whom the prosthesis was placed directly under the tympanic membrane or graft (n = 12). After 24 months, the mean pure-tone average air-bone gap was 24 dB (24% had ABG < or = 10 dB; 53% had ABG < or = 20 dB). Air-bone gap closures were stable over time. Our results demonstrated that Bioglass middle ear prostheses have excellent long-term tissue compatibility. The four failures are attributed to fractures in early experimental prototypes.
Article
The deterioration of cancellous bone structure due to aging and disease is characterized by a conversion from plate elements to rod elements. Consequently the terms "rod-like" and "plate-like" are frequently used for a subjective classification of cancellous bone. In this work a new morphometric parameter called Structure Model Index (SMI) is introduced, which makes it possible to quantify the characteristic form of a three-dimensionally described structure in terms of the amount of plates and rod composing the structure. The SMI is calculated by means of three-dimensional image analysis based on a differential analysis of the triangulated bone surface. For an ideal plate and rod structure the SMI value is 0 and 3, respectively, independent of the physical dimensions. For a structure with both plates and rods of equal thickness the value lies between 0 and 3, depending on the volume ratio of rods and plates. The SMI parameter is evaluated by examining bone biopsies from different skeletal sites. The bone samples were measured three-dimensionally with a micro-CT system. Samples with the same volume density but varying trabecular architecture can uniquely be characterized with the SMI. Furthermore the SMI values were found to correspond well with the perceived structure type.
Article
Calcium hydroxyapatite ceramics (CHA) are nontoxic materials, provoke little reaction from tissues, and by virtue of these properties represent a good starting point for creating bone substitutes. Although several porous CHAs have been used clinically, there have been few reports that CHA is fully replaced by newly formed bone, which may be due to its structure and the limited connectivity between pores. We recently developed a fully interconnected porous CHA (IP-CHA) by adopting a "foam-gel" technique. Structural analysis by scanning electron microscopy revealed that IP-CHA had spherical pores of uniform size that were interconnected by window-like holes. The surface of the wall structure was smooth, and hydroxyapatite particles were bound tightly to one another. Most of the interpore connections of IP-CHA ranged from 10 to 80 microm in diameter (average, 40 microm). When the cylindrical IP-CHA (diameter, 6 mm; height, 15 mm) was implanted into a rabbit femoral condyle, bone, and bone marrow with abundant vessels formed deep in the pores through the interpore connections. Within a period of 6 weeks, new bone had formed and penetrated to a distance of 3 mm from the surface of the IP-CHA implant. Furthermore, a compression test at 9 weeks revealed that the implanted IP-CHA steadily increased in strength to more than double the value of the initial test. These results indicate that the IP-CHA may have clinical utility as a superior bone substitute.
Article
Porosity and pore size of biomaterial scaffolds play a critical role in bone formation in vitro and in vivo. This review explores the state of knowledge regarding the relationship between porosity and pore size of biomaterials used for bone regeneration. The effect of these morphological features on osteogenesis in vitro and in vivo, as well as relationships to mechanical properties of the scaffolds, are addressed. In vitro, lower porosity stimulates osteogenesis by suppressing cell proliferation and forcing cell aggregation. In contrast, in vivo, higher porosity and pore size result in greater bone ingrowth, a conclusion that is supported by the absence of reports that show enhanced osteogenic outcomes for scaffolds with low void volumes. However, this trend results in diminished mechanical properties, thereby setting an upper functional limit for pore size and porosity. Thus, a balance must be reached depending on the repair, rate of remodeling and rate of degradation of the scaffold material. Based on early studies, the minimum requirement for pore size is considered to be approximately 100 microm due to cell size, migration requirements and transport. However, pore sizes >300 microm are recommended, due to enhanced new bone formation and the formation of capillaries. Because of vascularization, pore size has been shown to affect the progression of osteogenesis. Small pores favored hypoxic conditions and induced osteochondral formation before osteogenesis, while large pores, that are well-vascularized, lead to direct osteogenesis (without preceding cartilage formation). Gradients in pore sizes are recommended for future studies focused on the formation of multiple tissues and tissue interfaces. New fabrication techniques, such as solid-free form fabrication, can potentially be used to generate scaffolds with morphological and mechanical properties more selectively designed to meet the specificity of bone-repair needs.
Article
Three-dimensional (3D), highly porous, mechanically competent, bioactive and biodegradable scaffolds have been fabricated for the first time by the replication technique using 45S5 Bioglass powder. Under an optimum sintering condition (1000 degrees C/1h), nearly full densification of the foam struts occurred and fine crystals of Na2Ca2Si3O9 formed, which conferred the scaffolds the highest possible compressive and flexural strength for this foam structure. Important findings are that the mechanically strong crystalline phase Na2Ca2Si3O9 can transform into an amorphous calcium phosphate phase after immersion in simulated body fluid for 28 days, and that the transformation kinetics can be tailored through controlling the crystallinity of the sintered 45S5 Bioglass. Therefore, the goal of an ideal scaffold that provides good mechanical support temporarily while maintaining bioactivity, and that can biodegrade at later stages at a tailorable rate is achievable with the developed Bioglass-based scaffolds.
Article
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.