Development of microfibers for bone regeneration based on alkali-free bioactive glasses doped with boron oxide

In this paper, we present a new series of alkali-free bioactive glasses (BG) based on FastOs^® composition (38.49 SiO₂ – 36.07 CaO – 19.24 MgO – 5.61 P₂O₅ – 0.59 CaF₂, expressed in mol %), which was modified by partially replacing silicon dioxide network-former with boron trioxide network-former, utilizing calcium oxide as a charge compensator. The main objective of this study was to obtain a new family of bioactive glasses suitable for the fabrication of glass fibers. The BGs were prepared by melt quenching technique and their structural and thermal properties were determined. Glass rods were used to obtain fibers by the classic drawing technique. The bioactivity of the fibers was subsequently assessed through immersion tests in simulated body fluid (SBF) to establish their ability to form hydroxyl carbonated (HCA) apatite onto their surfaces. Glasses with moderate substitution of SiO₂ with B₂O₃ exhibited enhanced thermal properties, allowing to significantly suppress the crystallization trend, and favoring to draw the fibers. The structure of the studied glasses was obtained by NMR spectroscopy. The structure-property correlations were established by their relationship to the configurational entropy. Smaller amounts of substitution resulted in larger entropy of the glasses. Moreover the SBF tests revealed an extensive formation of HCA, comparable to the parent FastOs^®BG composition, which assures fast bonding to the bone. Thus, presented glass fibers may be considered as promising materials for wool-like bone implants or as reinforcing constituent of biopolymer matrix composites.     

Calcium and Zinc Containing Bactericidal Glass Coatings for Biomedical Metallic Substrates

The present work presents new bactericidal coatings, based on two families of non-toxic, antimicrobial glasses belonging to B₂O₃–SiO₂–Na₂O–ZnO and SiO₂–Na₂O–Al₂O₃–CaO–B₂O₃ systems. Free of cracking, single layer direct coatings on different biomedical metallic substrates (titanium alloy, Nb, Ta, and stainless steel) have been developed. Thermal expansion mismatch was adjusted by changing glass composition of the glass type, as well as the firing atmosphere (air or Ar) according to the biomedical metallic substrates. Formation of bubbles in some of the glassy coatings has been rationalized considering the reactions that take place at the different metal/coating interfaces. All the obtained coatings were proven to be strongly antibacterial versus Escherichia coli (>4 log).     

Studies on novel bioactive glasses and bioactive glass-nano-HAp composites suitable for coating on metallic implants

A series of novel zinc oxide (ZnO) containing bioactive glass compositions in SiO₂-Na₂O-CaO-P₂O₅ system and composite with hydroxyapatite (HAp) nano-particles were developed and applied as coating on Ti-6Al-4V substrates. The bioactive glasses and their composites were also processed to yield dense scaffolds, porous scaffolds and porous bone filler materials. The coating materials and the coatings were characterized and evaluated by different in vitro techniques to establish their superior mechanical properties. The cytotoxicity test of the coating material, porous and dense scaffolds and coated specimens showed non-cytotoxicity, biocompatibility and promising in vitro bioactivity for all tested samples. The dissolution behaviour studies of the bioactive glasses and the composites in simulated body fluid showed promising in vitro release pattern and bioactivity for all tested samples. Addition of nanosized HAp improves mechanical properties of the bioactive glass coating without affecting the in vitro bioactivity.     

Stress–corrosion cracking by indentation techniques of a glass coating on Ti6Al4V for biomedical applications

The fixation of bone replacement implants to the hosting tissue can be improved if the implants have a bioactive surface that can precipitate hydroxyapatite in vivo. Titanium alloys, despite their desirable mechanical and nontoxic properties, are not bioactive and do not bond directly to the bone. One of the ways to change a bioinert metallic surface such as a titanium alloy is to coat it with a bioactive material. This work presents the microstructural and stress–corrosion cracking characterization of two glass coatings on Ti6Al4V with different SiO₂ contents (61% and 64%). These coatings belong to the SiO₂–CaO–MgO–Na₂O–K₂O–P₂O₅ system and they were obtained by a simple enamelling technique. They will be used as the first layer of a bioactive multilayer system which will have an outer layer with a lower SiO₂ content in order to ensure the surface bioactivity. Microstructural characterization performed by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) shows that the coating porosity is clearly influenced by the firing time because of the longer extension of the reaction between Ti and SiO₂. The X-ray diffraction (XRD) integration method shows that the amount of crystalline phase (2.4CaO 0.6Na₂O P₂O₅) percentage is between 3 vol.% and 16 vol.%. After acid etching, a microstructure with clear boundaries is observed which is the result of the sintered glass particles separation. Stress–corrosion cracking was evaluated using Vickers and Hertzian (spherical) indentation, showing that both coatings are sensitive to subcritical crack growth, and that the coating with the lower silica content is more sensitive to stress–corrosion cracking. These two results are related with the larger residual stresses due to the thermal expansion mismatch. Finally, the stress–corrosion ring cracking behavior by Hertzian indentation is rationalized from the linear-elastic fracture mechanics framework.     

Sodium is not essential for high bioactivity of glasses

This study aims to demonstrate that excellent bioactivity of glass can be achieved without the presence of an alkali metal component in glass composition. In vitro bioactivity of two sodium-free glasses based on the quaternary system SiO₂-P₂O₅-CaO-CaF₂ with 0 and 4.5 mol% CaF₂ content was investigated and compared with the sodium-containing glasses with equivalent amount of CaF₂. The formation of apatite after immersion in Tris buffer was followed by Fourier-transform infrared spectroscopy, X-ray diffraction, ³¹P and ¹⁹F solid-state MAS-NMR. The dissolution study was completed by ion release measurements in Tris buffer. The results show that sodium-free bioactive glasses formed apatite at 3 h of immersion in Tris buffer, which is as fast as the corresponding sodium-containing composition. This signifies that sodium is not an essential component in bioactive glasses and it is possible to make equally degradable bioactive glasses with or without sodium. The results presented here also emphasize the central role of the glass compositions design which is based on understanding of structural role of components and/or predicting the network connectivity of glasses.     

The Fluxing Effect of Mineral Material – Cullet Compositions on Enamel Glass

Enamel glasses are synthesized based on the Na₂O – B₂O₃ – Co₂O₃ – SiO₂ system, including perlite, nepheline concentrate, and cullet. The physicochemical and technological properties of the resulting glasses and one-layer coatings based on these glasses are considered. A comparative analysis of the fluxing effect of the nepheline - cullet and perlite-cullet compositions on glasses is carried out. The reference composition areas are shown to be suitable for the development of one-coat powdered glass enamels.     

Certain Physical Properties of Binary Glasses Depending on Their Structural Specifics

The concept of structural elements, whose interaction determines glass properties, is used to interpret the regularities of the dependence of the refractive index in binary glass on glass composition, certain results of the mass-spectrometric analysis of the glasses vapor in the Rb₂O - B₂O₃ system, and the data on small angle x-ray scattering for glasses in the Na₂O - SiO₂ and Li₂O - SiO₂ system. Methods for estimating the refractive index of binary glasses depending on their composition and structure are proposed and examples of such calculations for alkali-silicate glasses are given.__________Translated from Steklo i Keramika, No. 1, pp. 8 – 11, January, 2005.     

Studies on a novel bioactive glass and composite coating with hydroxyapatite on titanium based alloys: Effect of γ-sterilization on coating

A novel silicate based bioactive glass coating composition containing B₂O₃ and TiO₂ having matching thermal properties with that of Ti₆Al₄ V implants was developed and characterized. A conventional vitreous enamelling technique was used for coating small flat surface and curved surface of small rods. Hydroxyapatite (HAp) micro and nano-crystalline particles were used to prepare bioactive glass-HAp composite coating. Scratch testing was used to study the coating adhesion and its fracture behaviour under simulated conditions. As observed from scratch testing results, adhesion strength of the coating improved from 21 N normal load to 27 N and 32 N on addition of micro-HAp and nano HAp powder, respectively, to bioactive glass matrix. Further, sterilization of the coated samples with 25 kGy gamma irradiation substantially enhanced the adhesion of glass coating and HAp-composite coating.     

Coupling sol-gel with electrospray deposition: Towards nanotextured bioactive glass coatings

For the first time, the sol-gel method was coupled with electrostatic spray deposition (ESD) to fabricate nanotextured bioactive glass (BG) coatings with a controlled microstructure in a one-pot-process. Three BG compositions belonging to the SiO₂-CaO-P₂O₅ system (S85, S75, and S58) were homogeneously deposited on metallic Ti6Al4V substrates starting from the atomization of precursor solutions. All coatings displayed an amorphous character, as confirmed by XRD. A wide variety of innovative BG morphologies were obtained, tuning the key parameters of ESD, leading from highly porous coral-like to compact reticular-type coatings. The bioactivity, in terms of apatite formation, of as-deposited coatings was tested by immersion in simulated body fluid solution. Textural properties were found to play an important impact in its biological performance. Highly porous ESD-coatings exhibited remarkable bioactivity for S75 and S58 compositions, compared with more compacted ones of equal formulations. S85 composition was found extremely reactive regardless of the coating microstructure.     

Effect of BaO substitution for CaO on the structural and thermal properties of SiO2–B2O3–Al2O3–CaO–Na2O–P2O5 bioactive glass system used for implant coating applications

The present study replaced 3.30 and 9.00 mol.% BaO for CaO in a SiO₂–B₂O₃–Al₂O₃–CaO–Na₂O–P₂O₅ bioactive glass system used for implant coating applications. Variations of the glass structure, thermal properties, cytotoxicity, and radiopacity of glasses were studied. As demonstrated by the results, upon adding barium oxide to the glass structure, the weight density increased significantly, while a slight decrease in oxygen density was determined. Introducing barium oxide into glass composition did not cause any considerable change in the spectra of FTIR and Raman. It was demonstrated that the amount of bridging oxygen in the glass structure remained quite unaffected. The hot stage microscopy evaluations revealed further shrinkage of barium-containing frits due to lower viscosity and hence, higher viscous flow of these glasses. By substituting barium oxide for calcium oxide and increasing its concentration, the glass transition temperature (T_g) and the dilatometric softening temperature (T_d) decreased, while the thermal expansion coefficient increased. Moreover, upon substituting 9 mol.% barium oxide for calcium oxide, a 30 °C reduction in maximum sintering temperature (T_ms) of the glass was obtained, whereas the shrinkage rate was increased 1.7 times. It was indicated that the sintering process of barium-incorporated glasses would easily proceed without any phase crystallization. The barium-incorporated glasses exhibited more radiopacity. Additionally, no cytotoxic effect was caused by the substitution, and the Ba-containing glasses could be used for biomedical applications and implant coating as well.     

Chitosan/gelatin-based bioactive and antibacterial coatings deposited via electrophoretic deposition

The fabrication of biocompatible and antibacterial coatings on metallic implants remains a significant challenge for load-bearing orthopedic implants. This study focuses on the electrophoretic deposition of chitosan/gelatin/Ag-Mn doped mesoporous bioactive glass nanoparticles (Ag-Mn MBGNs) composite on the PEEK/bioactive glass layer (called as multi-structured coatings), which had been deposited electrophoretically on 316L stainless steel. The EPD parameters for the deposition of the chitosan/gelatin/Ag-Mn MBGNs coatings were optimized via Taguchi design of experiment approach. Scanning electron microscopy images confirmed that the chitosan/gelatin/Ag-Mn MBGNS layer was deposited on the PEEK/BG layer. The addition of biologically active metallic ions (Mn and Ag) and molecules (chitosan) showed a strong effect on the growth of bacteria. Moreover, the inclusion of Mn and Ag showed a negligible toxic effect on the bioactivity (the ability of the coating to form a bond with the natural bone) of the coatings. Furthermore, the multi-structured coatings presented appropriate wettability and surface roughness for orthopedic applications. Overall, this study provides a direct solution to improve the bioactivity, antibacterial activity, and surface properties of deposited chitosan/gelatin coatings on orthopedic implants that are more manufacturable and translational from research to an industrial scale.     

Correlation between microstructure and properties of biocomposite coatings

A SiO₂–CaO–Na₂O (SCN) based bioactive glass was used to prepare glass–matrix/Ti particle composite coatings (SCNT). The coatings were obtained by vacuum plasma spray (VPS) on Ti–6Al–4V substrates. Two different deposition methods have been compared: (a) VPS of powders obtained by ball milling of sintered composites; (b) in situ plasma spray of mixed titanium and glass powders. For comparative purposes, pure SCN glass coatings were produced. The coating morphology and microstructure were observed by optical and scanning electron microscopy, compositional analyses by energy dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). Comparative mechanical tests were carried out by shear tests and by Vickers indentations at the interface between the substrate and the coatings. The bioactivity of glass- and composite coatings was investigated in vitro by soaking them in a simulated body fluid (SBF) with the same ion concentration of the human plasma. All the layers retain their starting composition. The composite coatings obtained by VPS of the powdered presintered composites showed a better mechanical behaviour with respect both to the composite coatings obtained by the in situ method and to the pure glass coatings. Both the glass- and the two kind of composite coatings revealed to be bioactive by the growth of a thick apatite layer after 30 days of soaking in SBF. The electrochemical behaviour of the SCNT coatings was evaluated by means of potentiodynamic anodic polarization curves and free corrosion potential measurements in Ringer solution at 25 °C. For comparative purposes the same analyses were performed on analogous bioactive glass-matrix/Ti particle composite coated samples, based on the system TiO₂–SiO₂–CaO–B₂O₃ (TSCB), and obtained both by the in situ and by presintering method as well. The results of the electrochemical tests showed a better corrosion behaviour of the samples coated by VPS of powdered sintered composites with respect to those coated by in situ VPS composites.     

Properties, Structure, and Application of Low-Melting Lead–Bismuth Glasses

Glass formation, crystallization, and physicochemical properties, as well as glass structure in the system PbO – ZnO – Bi₂O₃ – B₂O₃ – SiO₂, are investigated in the section with a constant molar content of glass-formers (B₂O₃ + SiO₂) equal to 20%. A nonlinear dependence of glass properties on their composition is established caused by the change of the coordination state of lead ion in glass structure. The developed glasses are recommended for joint and seals in the production of a new generation of physical parameter sensors.     

Direct ink writing of highly bioactive glasses

Direct ink writing (DIW), or Robocasting, is an additive manufacturing technique that offers the opportunity to create patient specific bioactive glass scaffolds and high strength scaffolds for bone repair. The original 45S5 Bioglass^® composition crystallises during sintering and until now, robocast glass scaffolds contained at least 51.9 mol% SiO₂ or B₂O₃ to maintain their amorphous structure. Here, ICIE16 and PSrBG compositions, containing <50 mol% SiO₂, giving silicate network connectivity close to that of 45S5, were robocast and compared to 13–93 composition. Results showed Pluronic F-127 can be used as a universal binder regardless of glass reactivity and that particle size distribution affected the ink “printability”. Scaffolds with interconnects of 150 μm (41–43% porosity) had compressive strengths of 32–48 MPa, depending on the glass composition. Robocast scaffolds from these highly reactive bioactive glasses promise greatly improved bone regeneration rates compared with existing bioactive glass scaffolds.     

Phosphate content affects structure and bioactivity of sol-gel silicate bioactive glasses

Bioactive glasses can heal bone defects and bond with bone through formation of hydroxyl carbonate apatite (HCA) surface layer. Sol-gel derived bioactive glasses are thought to have potential for improving bone regeneration rates over melt-derived compositions. The 58S sol-gel composition (60 mol% SiO₂, 36 mol% CaO, and 4 mol% P₂O₅) has appeared in commercial products. Here, hydroxyapatite (HA) was found to form within the 58S glass during sol-gel synthesis after thermal stabilization. The preformed HA may lead to rapid release of calcium orthophosphate, or nanocrystals of HA, on exposure to body fluid, rather than the release of separate the calcium and phosphate species. Increasing the P₂O₅ to CaO ratio in the glass composition reduced preformed HA formation, as observed by XRD and solid-state NMR. Instead, above 12 mol% phosphate, a phosphate glass network (polyphosphate) formed, creating co-networks of phosphate and silica. Nanopore diameter of the glass and rate of HCA layer formation in simulated body fluid (SBF) decreased when the phosphate content increased.     

Synthesis,Characterization, and In Vitro Bioactivity of Sol‐Gel‐Derived Zn,Mg, and Zn‐Mg Co‐Doped Bioactive Glasses

Bioactive glasses in the systems CaO‐SiO₂‐P₂O₅‐ZnO, CaO‐SiO₂‐P₂O₅‐MgO, and CaO‐SiO₂‐P₂O₅‐MgO‐ZnO were prepared and characterized. Bioactive glass powders were produced by the sol‐gel method. The prepared bioactive glass powders were immersed in a simulated body fluid (SBF) for periods of up to 28 days at 310 K to investigate the bioactivity of the produced samples. Inductively coupled plasma (ICP) and ultraviolet (UV) spectroscopic techniques were used to detect changes in the SBF composition. X‐Ray diffraction (XRD) was utilized to recognize and confirm the formation of a hydroxyapatite (HA) layer on the bioactive glass powders. Microstructural characterizations of the bioactive glass samples were investigated by scanning electron microscopy (SEM) techniques. Density, porosity, and surface area values of bioactive glass powders were also determined in order to characterize the textural properties of the samples. The results revealed the growth of an HA layer on the surface of the bioactive glass samples. MgO in the glass sample increases the rate of formation of an HA layer while ZnO in the glass slows it down.     

Surface finish of low-boron zirconium glazes

The present study was concerned with glasses and glazes in the system Na₂O?CaO?B₂O₃?Al₂O₃?SiO₂?ZrO₂ low in B₂O₃. The manner in which the composition, firing temperature, and holding period can influence the quality and finish of coatings was investigated. The properties of the coatings, such as gloss, whiteness, refractive index, and TCLE, were determined.     

Factors governing the sinterability,In vitro dissolution,apatite formation and antibacterial properties in B2O3 incorporated S53P4 based glass powders

In this report, we have systematically evaluated the role of boron in regulating the degradation, apatite formation and antibacterial properties of bioactive glasses by substituting SiO₂ with B₂O₃ in S53P4 based glass composition. The structural analysis of the glasses has been carried out using neutron diffraction and Raman spectroscopic techniques. The structural analysis of S53P4 base glass has revealed the presence of silicate and phosphate units in the form of Q²_Si, Q³_Si and isolated Q⁰_P units. With the increasing replacement of SiO₂ with B₂O₃, Raman spectroscopy revealed the formation of non-ring metaborate units and borate rings consisting of both BO₃ and BO₄ units at the expense of Q²_Si and Q³_Si units. Furthermore, DSC, HSM and dilatometry results confirmed that the sinterability parameter (S_c) and fragility index (m) values of borosilicate bioactive glasses help in achieving superior sintering and thermal processing without devitrification. Additionally, in vitro SBF immersion studies revealed an accelerated release of Si⁴⁺ and Ca²⁺ ions from the borosilicate glasses. In vitro antibacterial assays against E.coli bacterial inoculum illustrate the critical role of B₂O₃ in the bioactive glass composition.     

THE EFFECTS OF ADDITIONS OF ZINC OXIDE AND CADMIUM OXIDE ON SIMPLE GLASSES1

The glass consisted of the composition SiO₂ 58%, PbO 22%, and Na₂O 20%. Zinc oxide was introduced in increments of 5% up to a maximum of 20% as a substitute for equivalent parts of Na₂O. Similar substitutions were made with cadmium oxide. The following physical properties were studied: thermal expansions, solubilities in hydrochloric acid, indices of refraction, and annealing conduct. Analyses of the glasses were made. The suitability of these glasses as vitreous enamels is discussed. A vacuum electric furnace for melting and fining glass under reduced pressures is described.     

Effect of low temperature crystallization on 58S bioactive glass sintering and compressive strength

Mesoporous glass 58S (60SiO₂, 36CaO, 4P₂O₅ mol.%) has excellent bioactivity, biocompatibility, and forms strong bonds with bone making it attractive for implants. Mesoporous bioactive glass 58S powder is typically consolidated through sintering in order to produce an implant with sufficient strength to withstand the in vivo loads. However, heating the glass often leads to crystallinity, which is undesirable because it can reduce bioactivity. Hence, there is a trade-off between minimising crystallinity and maximising glass strength. Even at relatively low temperatures, it has been suggested that segregation of calcium and phosphate from silica within the glass can lead to crystallization. In this work, we confirm the occurrence of low temperature segregation in bioactive glass 58S using electron microscopy with elemental mapping. We probe how segregation affects the material properties of post-sintered glasses via comparison to a glass where phase separation is prevented via addition citric acid to the parent sol.