Can the regenerative potential of an alkali-free bioactive glass composition be enhanced when mixed with resorbable β-TCP?

The addition of resorbable β-tricalcium phosphate (β-TCP) to other bone substitute materials such as hydroxyapatite (HA) has been pointed out as a suitable strategy to enhance the regenerative potential of bone grafts made thereof. To check the generalization of this hypothesis, a new synthetic composite bone graft material consisting of a mixture of 30 vol% of pure β-TCP and 70 vol% of FastOs^®BG (an alkali-free bioactive glass - BG) was prepared and tested in vivo. The in vivo performance of the new synthetic bone graft (30β-TCP-70FastOs^®BG) was compared with those of FastOs^®BG alone and of adbone^®BCP, a biphasic calcium phosphate, consisting of 75% of HA and 25% of β-TCP. Two defects with 4 mm diameter were performed in Wistar rats calvaria and filled with the bone graft materials. The animals were sacrificed after 9 weeks of implantation and the calvaria was excised. Empty bone defects were used as negative control. The percentages of new bone formed (von Kossa staining) were always higher in the treated groups (FastOs^®BG, 30β-TCP-70FastOs^®BG and adbone^®BCP) than in empty group. There were differences with statistical significance between empty and FastOs^®BG groups and between empty and adbone^®BCP groups. But the differences observed between empty and 30β-TCP-70FastOs^®BG groups were less remarkable. The results demonstrated the superior bone regeneration ability of FastOs^®BG alone, which was not further enhanced by adding β-TCP in the composition, confirming its already proven regenerative potential.     

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.     

Bioactivity behaviour of biodegradable material comprising bioactive glass

Biocomposite of bioactive glass (BG) with chitosan polymer (CH) is prepared by freeze-drying technique. Obtained material is investigated by using several physico-chemical methods. The XRD and FTIR show the interface bonding interactions between glass and polymer. The specific surface and porosity of biocomposite were determined. In vitro assays were employed to evaluate the effect of chitosan addition on the glass by studying the chemical reactivity and bioactivity of the BG and BG/CH biocomposite after soaking in a simulated body fluid (SBF). The obtained results show the formation of a bioactive hydroxycarbonate apatite (HCA) layer and highlight the bioactivity and the kinetics of chemical reactivity of bioactive glass, particularly after association with chitosan. The BG/CH biocomposite has excellent ability to form an apatite layer. Inductively coupled plasma-optical emission spectrometry (ICP-OES) highlights the negative effect of chitosan on the silicon release toward the SBF of bioactive glass when in vitro assays.     

Magnetic and bioactive properties of MnO2/Fe2O3 modified Na2O-CaO-P2O5-SiO2 glasses and nanocrystalline glass-ceramics

Glass and in-situ nanocrystalline glass-ceramics of compositions 45SiO₂-25CaO-10Na₂O-5P₂O₅-xFe₂O₃-(15-x) MnO₂ are investigated for their magnetic and in-vitro bioactive properties. The ferrimagnetic character is observed in the high Fe₂O₃ containing in-situ nanocrystalline glass-ceramics. Saturation magnetization and coercivity increases with Fe₂O₃. After soaking in the simulated body fluid (SBF), the powdered as well as the bulk glasses and glass-ceramics are investigated using various characterization techniques. The presence of MnO₂ increases the leaching of Na⁺ ions from the glasses and also attracts the Ca²⁺ cations from the SBF as compared to Fe₂O₃ containing nano-crystalline glass-ceramics. It also increases the tendency to form hydroxyl apatite (HAp) layer. Microwave Plasma Atomic Emission Spectroscopy (MP-AES), Fourier Transform Infrared (FTIR) spectra, X-ray diffraction and Scanning electron micrographs (SEM) after soaking in the SBF confirm the HAp formation on the surface of all the glasses and glass-ceramics. Urbach energy also indicates the structural modifications on the surfaces of the glass and glass-ceramics after soaking in the SBF.     

Effects of Sr and Mg dopants on biological and mechanical properties of SiO2–CaO–P2O5 bioactive glass

In the present study, the effects of Sr and Mg were investigated on mechanical and biological properties of 58S bioactive glass (BG). SiO₂-P₂O₅-CaO BG with different contents of Sr and Mg were synthesized via the sol-gel method and immersed in simulated body fluid (SBF) for several days to explore their biocompatibility. Precise analyses of the BG using X-ray powder diffraction, scanning electron microscopy, and transmission electron microscopy showed that the Mg-doped BG containing 8 wt % MgO possessed better biocompatibility. It was also found that mechanical properties of the BG could be improved by increasing the amounts of MgO and SrO. Both 5Sr-BG and 8Mg-BG samples did not exhibit any cytotoxicity while showing high alkaline phosphatase activity in comparison with control specimens. However, the Sr-doped BG sample including 5 wt % SrO demonstrated enhanced bioactivity and biocompatibility.     

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.     

Gel-derived SiO2–CaO–P2O5 bioactive glasses and glass-ceramics modified by SrO addition

The effect of SrO substitution for CaO in two sol–gel glasses with different chemical compositions (mol%) A2Sr: (54−x)CaO–xSrO–6P₂O₅–40SiO₂ and S2Sr: (16−x)CaO–xSrO–4P₂O₅–80SiO₂ (x=0, 1, 3 and 5) stabilized at 700 °C on their structure (XRD, FTIR) and bioactive properties (SBF test) was investigated. Preliminary in vitro tests using human articular chondrocytes of selected A2Sr glass were also conducted. Moreover, the subject of this study was to detect the changes on material properties after heat treatment at 1300 °C. The results show that the effect of strontium substitution on structure, bioactivity and crystallization after treatment at both the above temperatures strongly depends on CaO/SiO₂ molar ratio. The presence of 3–5 mol% of strontium ions creates more expanded glass structure but does not markedly affect crystallization ability after low temperature treatment. Sintering at 1300 °C of A2 type glasses results in crystallization of pseudowollastonite, hydroxyapatite and also Sr-substituted hydroxyapatite for 3–5 mol% of SrO substitution. The increase of strontium concentration in silica-rich materials after sintering leads to appearance of calcium strontium phosphate instead of calcium phosphate. Bioactivity evaluation indicates that substitution of Sr for Ca delays calcium phosphate formation on the materials surface only in the case of silica-rich glasses treated at 700 °C. Calcium-rich glasses, after both temperature treatments, reveals high bioactivity, while crystal size of hydroxyapatite decreases with increasing Sr content. High temperature treatment of high-silica glasses inhibits their bioactivity. Preliminary in vitro tests shows Sr addition to have a positive effects on human articular chondrocytes proliferation and to inhibit cell matrix biomineralization.     

Synthesis and in vitro bioactivity assessment of injectable bioglass−organic pastes for bone tissue repair

The aim of this work was to study the bioactivity of systems based on a clinically tested bioactive glass (BG) particulates (mol%: 4.33 Na₂O−30.30 CaO−12.99 MgO−45.45 SiO₂−2.60 P₂O₅−4.33 CaF₂) and organic carriers. The cohesiveness of injectable bone graft products is of high relevance when filling complex volumetric bone defects. With this motivation behind, BG particulates with mean sizes within 11−14 μm were mixed in different proportions with glycerol (G) and polyethylene glycol (PEG) as organic carriers and the mixtures were fully injectable exhibiting Newtonian flow behaviors. The apatite forming ability was investigated using X-ray diffraction and field emission scanning electron microscopy under secondary electron mode after immersion of samples in simulated body fluid (SBF) for time durations varying between 12 h and 7 days. The results obtained revealed that in spite of the good adhesion of glycerol and PEG carriers to glass particles during preparation stage, they did not hinder the exposure of bioactive glass particulates to the direct contact with SBF solution. The results confirmed the excellent bioactivity in vitro for all compositions expressed by high biomineralization rates with the formation of crystalline hydroxyapatite being identified by XRD after 12 h of immersion in SBF solution.     

Synthesis,Characterization and Biological Evaluation of a New Sol-Gel Derived B and Zn-Containing Bioactive Glass: <Emphasis Type="Italic">In Vitro</Emphasis> Study

In this study we employed the sol-gel method to synthesize new CaO–P₂O₅–SiO₂–ZnO–B₂O₃ bioactive glasses. Three samples with various B₂O₃ content (5, 10 and 15 mol %) was prepared and their bioactivity were evaluated by immersion in simulated body fluid (SBF) and the glasses were characterized using X-ray diffraction (XRD), Fourier transform infrared (FTIR) and scanning electron microscopy (SEM). The experimental results revealed that with increasing the amount of boron content, a more crystalline domain can be observed in their XRD patterns and consequently the formation of hydroxyapatite (HA) increased. FTIR spectra showed that the sample containing 10 mol% of boron had the sharpest peaks attributed to the formation of hydroxyapatite. Biocompatibility of the samples was examined by MTT assay and alkaline phosphatase activity. The result ascertained that the synthesized bioactive glass had good biocompatibility and can serve as a bone substitute in bone defects.     

Bioactivity and antibacterial activity against E-coli of calcium-phosphate-based glasses: Effect of silver content and crystallinity

In this work we developed improved bioactive glasses and glass-ceramics for biomedical applications, investigating their in vitro bioactivity, biocompatibility and antibacterial properties against E-Coli. A melt-quenched bioactive glass of the SiO₂-CaO-P₂O₅-MgO system was modified with the addition of 1 and 2 mol% Ag₂O and the 1 mol% Ag₂O-containing glasses were then heat treated to produce glass-ceramics. Surface modifications after soaking in SBF and ionic concentration changes showed that addition of silver and crystallization did not affect bioactivity although crystalline phases promoted a decrease in the degradation rate.Biocompatibility of all Ag-containing glasses and glass-ceramics was confirmed for certain samples concentrations. The antibacterial activity of the glasses against E-Coli was generally improved with decreasing particle size or increasing Ag₂O. The Ag-containing glass-ceramics with higher content of crystalline phase appears as a promising biocompatible biocidal material with potential applications in bone-related diseases.     

Quaternary bioactive glass-derived powders presenting submicrometric particles and antimicrobial activity

The biomedical engineering advances in the last years have been rising demand for multifunctional biomaterials. Bioactive glass (BG) submicron particles are potential candidates for the formulation of composites with improved dispersion and homogeneity between the constituents. This work presents the preparation of SiO₂–Na₂O–CaO–P₂O₅ glass-derived powders composed of particles with homogenous shapes and sizes between 300 and 500 nm. Two types of synthesis were employed for the preparation of the BG powders, the melt-quenching method, and a citric acid-assisted sol-gel route at a low citric acid concentration (0.005 mol L^?1). The morphology of the particles was achieved by a low-energy process using a ball mill. These powders were characterized for their structure and surface area and evaluated for in vitro mineralization and antibacterial behavior. X-ray diffraction (XRD) analysis revealed different crystalline silicate phases in the sol-gel-derived powder and confirmed the amorphous structure of the melt-quenching-derived one. The surface of the particles was covered by hydroxycarbonate-apatite (HCA) after five days in simulated body fluid (SBF). The antibacterial activity against Staphylococcus aureus was higher for the sol-gel-derived powder, showing inhibition >99% of the bacteria growth in 24 h for all concentrations studied. These BG-based powders present a set of characteristics useful for the formulation of multifunctional composites for orthopedic applications.     

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.     

A novel strategy to synthesize bioactive glass based on the eutectic reaction of B2O3–K2O

Melt-derived route was used to prepare modified bioactive glass-ceramic based on the 45S5 composition with the same network connectivity. Their phase composition, sinterability, and bioactivity were studied. A modified composition was proposed using potassium tetraborate (K₂B₄O₇) to reduce the melting temperature during manufacture. The phase composition and the bioactivity was determined by X-ray diffraction and Fourier transform infrared spectroscopy. Furthermore, the antibacterial properties were evaluated against Enterococcus faecalis. The result shows that glass-ceramics already had P–O and C–O bond functional groups on day 2. These bonds are responsible for the creation of the HCA layer. Scanning electron microscopy (SEM) pictures and Energy Dispersive X-ray Spectroscopy (EDX) investigations showed that, after being immersed in SBF solution, a layer of hydroxyapatite (HA) formed on both BG surfaces on day 2 and that by day 21, HCA cluster crystals had developed. Inductively coupled plasma-optical emission spectroscopy metrics of ionic release from the prepared glass-ceramic, mainly calcium and phosphorus ions in SBF solution, revealed that HCA formation occurred on both BG surfaces, which correlated to the increasing pH within 2 days of incubation; furthermore, it exhibited good antibacterial behavior against the Enterococcus faecalis.     

Effect of S53P4 bioactive glass content on structural and in-vitro behavior of hydroxyapatite/bioactive glass mixtures prepared by mechanical milling

This work presents silicon-substituted hydroxyapatite preparation through planetary ball milling using biogenic hydroxyapatite and different wt% of S53P4 bioactive glass (5, 10, 15, and 20 wt%) sources for the first time. The prepared mixtures showed a BHAp lattice contraction with SiO₄^4? incorporation; rich- and poor-Si phases were subsequently identified. Furthermore, two types of interaction among the functional groups in the S53P4 and BHAp mixtures are proposed. First, the 95-5 (wt.%) sample displayed a BHAp lattice with SiO₄^4?, CO₃^2?, and OH^? ions substitution. In samples with S53P4 BG content higher than 95-5, the lattice substitution was related to SiO₄^4?, PO₄^3?, and CO₃^2? ions, and a dehydroxylation process occurred in the BHAp. Finally, the bioactive behavior of the samples was studied by immersion in Hank's solution for 7, 14, and 28 days. The results showed that the mixtures formed a bone-like apatite layer with a dune-like morphology that increased in size and quantity with increasing S53P4 content in the mixtures.     

Effect of boron oxide on mechanical and thermal properties of bioactive glass coatings for biomedical applications

Bioactive glass coatings can improve the osteo integration of metallic implants with the host tissue, thereby increasing their lifespan and overall success rate. However, complex composition-structure-property relations in phosphosilicate-based bioactive glasses make experimental determination of these relations and related composition design of bioactive coatings challenging. By applying molecular dynamics (MD)-based atomistic simulations with recently developed effective potentials, this work addresses the challenge by using a material genome approach to obtain the composition and structure effects on various key properties for bioactive coating applications. A series of potential bioactive glass compositions were studied and the composition effects on the mechanical and thermal properties that are critical to these bioactive glasses as a coating to metallic implants were calculated. Particularly, by varying the level of B₂O₃ to SiO₂ substitutions, the effect of composition on various key properties was elucidated. It was found that by using cation in a 1 to 1 ratio (BO_3/2 to SiO₂) instead of the commonly used substitutions (B₂O₃ to SiO₂), the composition effect can be more clearly expressed and, hence, recommended in future composition designs. Together with careful structural analysis, the origin of property changes can be elucidated. The atomistic computer simulation-based approach is, thus, an effective way to guide future bioactive glass designs for bioactive coatings and other applications.     

Apatite formation on melt-derived bioactive glass powder based on SiO2-CaO-Na2O-P2O5 system

The higher melting temperature and longer soaking time during conventional glass melting route promoted the search for alternative in developing new bioactive glass (BG) composition with improved in fabrication temperature and melting time. The current project involved fabrication of new BG compositions based on SiO₂-CaO-Na₂O-P₂O₅ system via melt derived route. It was confirmed that all bioactive glass composition can be melted at temperature lower than 1400 °C. Formation of Si-O-Si (tetrahedral) functional group highlighted that silicate based glass was established as detected by Fourier transform infrared spectroscope (FTIR). BG bioactivity was performed by incubating the BG powder in Tris-buffer solution (pH 8) for 7, 14 and 21 days. In vitro test confirmed the apatite formation on the bioactive glass surface upon soaking in Tris-buffer solution with characteristic of carbonate group (C-O) and P-O band noticed from FTIR and present of crystalline peak observed in X-ray diffraction (XRD). Morphology of apatite formation on BG surface was observed using scanning electron microscope (SEM).     

Chemical durability and microstructural analysis of glasses soaked in water and in biological fluids

A new glass, obtained from Bioglass^® BG45S5 original composition by substituting CaO with MgO, was produced and its chemical durability and microstructural characteristics were compared with that of Bioglass^®.The two glasses (labelled as BG45 and MG45) were soaked up to 4 weeks at physiological temperature in different solutions, i.e. bi-distilled water, Hank's Buffered Salt Solution 61200 (labelled as HBSS+), Hank's Buffered Salt Solution 14170 (labelled as HBSS−), and Kokubo's SBF. Moreover, the influence of either flat or flake surfaces was analysed for both glasses. Results showed that the chemical durability of a glass in saline at 37 °C, evaluated through pH and ICP-AES chemical analysis of the leached components, depended mainly on the chemical composition of the soaking solution. Moreover, the MG45 glass never exhibited hydroxyapatite crystal formation on its surface also after soaking in calcium-containing solutions. The apatite crystallisation and deposition mechanism, typical of a bioactive glass, was induced only if the glass itself contained calcium. The contemporaneous presence of calcium in the glass and in the soaking solution improved the reactivity of the glass, as apatite crystals nucleated in a shorter time and grew more quickly. As regards the morphology of the glass surface, rougher surfaces favoured the formation of hydroxyapatite crystals on glasses containing calcium.     

Bioactive glass nanoparticles with negative zeta potential

The purpose of this work was to produce and characterize SiO₂–CaO–P₂O₅ bioactive glass nanoparticles with negative zeta potential for possible use in biomedical applications. 63S bioactive glass was obtained using the sol–gel method. X-ray fluorescence (XRF) spectroscopy and dispersive X-ray analysis (EDX) confirmed the preparation of the 63S bioactive glass with 62.17% SiO₂, 28.47% CaO and 9.25% P₂O₅ (in molar percentage). The in vitro apatite forming ability of prepared bioactive glass was evaluated by Fourier transform infrared spectroscopy (FTIR) after immersion in simulated body fluid (SBF). The result showed that high crystalline hydroxyapatite can form on glass particles. By the gas adsorption (BET method), particle specific surface area and theoretical particle size were 223.6 ± 0.5 m²/g and ∼24 nm, respectively. Laser dynamic light scattering (DLS) indicated particles were mostly agglomerated and had an average diameter between 100 and 500 nm. Finally, using laser Doppler electrophoresis (LDE) the zeta potential of bioactive glass nanoparticles suspended in physiological saline was determined. The zeta potential was negative for acidic, neutral and basic pH values and was −16.18 ± 1.8 mV at pH 7.4. In summary, the sol–gel derived nanoparticles revealed in vitro bioactivity in SBF and had a negative zeta potential in physiological saline solution. This negative surface charge is due to the amount and kind of the ions in glass structure and according to the literature, promotes cell attachment and facilitates osteogenesis. The nanometric particle size, bioactivity and negative zeta potential make this material a possible candidate for bone tissue engineering.     

Enhancing In Vitro Bioactivity of Melt‐Derived 45S5 Bioglass® by Comminution in a Stirred Media Mill

45S5 Bioglass^® (45S5 BG) is a frequently applied Type A bioactive material, capable of forming an inherent bond to bone and soft tissue. Currently, applied melt‐derived bioactive glass powders (BG) exhibit particle sizes between a few to several hundred micrometers. Recent studies on nanometer‐sized bioactive glasses (nBGs), produced by bottom‐up methods like sol–gel processing or flame spray pyrolysis, have indicated their great potential for several biomedical applications. In this study, the feasibility of top‐down processing starting from bulk 45S5 BG by wet comminution in a stirred media mill was investigated. The products were assessed by in vitro hydroxycarbonate apatite (HCAp) formation in simulated body fluid, which is a marker for bioactive behavior. The study reveals the paramount influence of the used solvent for a successful top‐down processing: In comparison with the as‐received material bioactivity is lost for powders processed in water, preserved for comminution in ethanol and increased for powders processed using the alcohols n‐butanol, n‐pentanol, and n‐hexanol. It was also found that only for the latter solvents, the chemical composition of the glass is maintained during comminution. Flake‐like, slightly porous particles with specific surface areas of ~25–30 m²/g are obtained. Thus, the presented comminution approach offers a convenient technique to process 45S5 BG with enhanced bioactivity.