Silicate Bioactive Glass Research Articles

Robocasting of Bioactive SiO2-P2O5-CaO-MgO-Na2O-K2O Glass Scaffolds.

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 μm and strut diameter 300 μm). 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.

Research progress of bioactive glasses based bone repair materials

Bioactive glasses (BGs) are a kind of biomaterials with osteoconductive and osteoinductive properties and are able to create a strong bond with host bone and promote osteogenesis after implantation. According to their compositions, bioactive glasses can be classified as silicate BGs, phosphate BGs, and borate BGs. Nowadays, silicate BGs are still the most common, while phosphate BGs and borate BGs have higher dissolution and degradation rates. Melt-quenching and sol-gel process are two basic methods to produce melt-derived BGs and sol-gel BGs, respectively. The latter requires lower heat treatment temperature with higher specific surface area and biological activity. Bioactive glass-ceramics can be obtained by heat treatment, which improves the mechanical strength but slightly reduces the bioactivity. Nano-bioactive glasses with the higher specific surface area can be obtained by changing the structure size of the materials by other treatment methods. On this basis, 3D BGs scaffolds can be made, and hybrid BGs scaffolds as well by combining with other biomaterials to obtain the 3D interconnected pores with the hierarchical or bionic structures, to enhance the mechanical strength, osteogenic activity and provide mechanical support suitable for the host bone. However, the bioactivity of BGs depends on the degradation rate, to some extent, which is contradictory to the mechanical strength. An appropriate porosity or controllable degradation rate can be selected to meet the common needs of early support and osteogenesis. In basic studies, it was found that BGs could act on cells by releasing ions or through the macropinocytosis pathway, up-regulating the expression of related genes or promoting osteogenesis. The degradation rates of BGs are related to their structures and compositions, which enables the quantitative prediction of the change of mechanical strength during degradation. Progress has also been made in structural mechanics and testing methods.

Effect of Silver on the Apatite Formation of Bioactive Silicate Glass

Abstract Silver (Ag) has the antibacterial property and can be easily introduced in glasses and glass-ceramics. In this research, the effect of Ag addition on the apatite formation of sol-gel derived new composition bioactive glass (BG) (55%SiO2 - 4% P2O5 -22%Na2O - (19-x) %CaO -x% Ag2O) (x=0, 5 and 8%) were investigated. The synthesized Ag doped BG samples were treated in Hank's Balanced Salt Solution (HBSS) for 14 days to study the bioactivity. The achieved samples were evaluated by X-ray powder diffraction (XRD) and Scanning electron microscope (SEM). The XRD spectra clearly show diffraction peaks of bone-like hydroxyapatite (HAp) for all samples after immersion in HBSS. However, the more intense of HAp peak at 32° was detected in Ag(5%) and Ag(8%) BGs compared with undoped BG. All glass samples are bioactive but BG with 8 wt% of Ag2O exhibited more apatite than the samples containing 5 wt% of Ag2O, as seen in SEM images. After 14 days immersion, full coverage of apatite in cluster crystal form on the Ag(8) glass surface was observed.

Crystallization behavior of SiO2–P2O5–CaO–MgO–Na2O–K2O bioactive glass powder

Abstract The crystallization process of a bioactive silicate glass with 47.5SiO2-10Na2O-10K2O-10MgO-20CaO-2.5P2O5 molar composition was investigated by using nonisothermal differential t hermal a nalysis (DTA). T he DTA plots recorded at different heating rates exhibited a single crystallization peak. The activation energy for crystallization was estimated by applying the equations proposed by Kissinger and Matusita-Sakka. The Johnson-Mehl-Avrami exponent (n) was assessed by using the Ozawa and Augis-Bennett methods. The analyses suggest that a surface crystallization mechanism with one-dimensional crystal growth is predominant. The activation energy for viscous flow was also assessed (176 kJ/mol) and was found lower than the activation energy for crystallization (271 kJ/mol). This confirms the stability of 47.5B against crystallization and its good sinterability, which is a highly attractive feature for producing glass products of biomedical interest, such as bioactive porous scaffolds for bone repair.

Cellular Response to 3-D Printed Bioactive Silicate and Borosilicate Glass Scaffolds.

The repair and regeneration of loaded segmental bone defects is a challenge for both materials and biomedical science communities. Our recent work demonstrated the capability of bioactive glass in supporting bone healing and defect bridging using a rabbit femur segmental defect model without growth factors or bone marrow stromal cells (BMSCs). Here in the current work, a comprehensive in vitro evaluation of bioactive silicate (13-93) and borosilicate (2B6Sr) glass scaffolds was conducted to provide further understanding of their biological performances and to establish a correlation between in vitro and in vivo behaviors. Our in vitro evaluation using a murine MC3T3-E1 cell line confirmed the capability of both scaffolds to support cell attachment, vascular endothelial growth factor (VEGF) formation, and to stimulate mineral deposition and osteoblast marker gene expression. In particular, borosilicate (2B6Sr) glass showed a better capability in supporting the mineralization and gene expression than silicate (13-93) glass, consistent with a faster bone healing ability in vivo. The current in vitro results, combined with our previous in vivo findings, provide a strong basis for the further translational evaluation of bioactive glass scaffolds and for potential preclinical practice. © 2018 Wiley Periodicals, Inc. J. Biomed. Mater. Res. Part B, 2018. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 818-824, 2019.

The effect of S53P4-based borosilicate glasses and glass dissolution products on the osteogenic commitment of human adipose stem cells.

Despite the good performance of silicate bioactive glasses in bone regeneration, there is considerable potential to enhance their properties by chemical modifications. In this study, S53P4-based borosilicate glasses were synthesized and their dissolution profile was studied in simulated body fluid by assessing pH change, ion release and conversion to hydroxyapatite. The viability, proliferation, attachment, osteogenesis and endothelial marker expression of human adipose stem cells (hASCs) was evaluated upon direct culture on glass discs and in the extract medium. This is the first study evaluating cell behavior in response to borosilicate glasses based on S53P4 (commercially available as BonAlive®). Replacing silicate with borate in S53P4 increased the glass reactivity. Despite the good viability of hASCs under all conditions, direct culture of cells on borosilicate discs and in undiluted extract medium reduced cell proliferation. This was accompanied with changes in cell morphology. Regarding osteogenic commitment, alkaline phosphatase activity was significantly reduced by the borosilicate glass discs and extracts, whereas the expression of osteogenic markers RUNX2a, OSTERIX, DLX5 and OSTEOPONTIN was upregulated. There was also a borosilicate glass-induced increase in osteocalcin protein production. Moreover, osteogenic supplements containing borosilicate extracts significantly increased the mineral production in comparison to the osteogenic medium control. Interestingly, borosilicate glasses stimulated the expression of endothelial markers vWF and PECAM-1. To conclude, our results reveal that despite reducing hASC proliferation, S53P4-based borosilicate glasses and their dissolution products stimulate osteogenic commitment and upregulate endothelial markers, thus supporting their further evaluation for regenerative medicine.

Magnesium calcium silicate bioactive glass doped with copper ions; synthesis and in-vitro bioactivity characterization

Recent studies revealed that metallic ions have therapeutic effects on human bone metabolism and angiogenesis. Thus, in this study, a new magnesium-calcium-silicate glass powder, being doped with copper ions was synthesized through the sol-gel process; the material was termed as 60S7M2Cu. The glass was thermally treated at several temperatures up to 870 °C in order to induce crystallization, which would potentially enhance its mechanical and/or biological properties. Structural and morphological characterization, thermal analysis and in-vitro apatite forming ability evaluation were performed by X-ray diffraction-XRD, Scanning Electron Microscopy-SEM coupled with Energy Dispersion Spectrometry-EDS, Thermogravimetric Analysis, as well as Fourier Transformed Infrared-FTIR Spectrometry. Moreover, the elemental release was recorded by Inductively Coupled Plasma Atomic Emission Spectroscopy ICP-AES. Experimental results showed that a crystalline hydroxyapatite phase was developed after 3 days in the simulated body fluid (SBF) followed, after 15 days, by the growth of a carbon hydroxyapatite layer, in both untreated glass as well as treated glass-ceramics nearly at all temperatures. At lower temperatures, namely 770 and 800 °C, a whitlockite bioactive phase appeared after the immersion in SBF, while a wollastonite crystalline phase emerged when treated at 830 and 870 °C without having a negative effect on its apatite forming ability. Copper ions releasing from the glass and glass-ceramics materials was proved to be slow and stable during the whole period of soaking. In this study copper containing glass and glass-ceramics, which present apatite forming ability and according to literature possess the capability to induce the release of therapeutic ions with osteogenic and angiogenic capacity, were synthesized. Eventually, after further investigations, this glass composition could be applied in bone tissue engineering, where bioactive materials able to induce simultaneously both osteogenesis and angiogenesis constitute a constant demand.

An atomic-level look at the structure-property relationship of cerium-doped glasses using classical molecular dynamics

Ce-containing bioactive glasses are of great interest in biomedical field since they exert antioxidant properties associated with low toxicity and a broad spectrum of bacteriostatic activities. The results obtained by classical molecular dynamics simulations allow the elucidation of the correlations between the effect of the inclusion of cerium doping ions into the structure of phosphosilicate and silicate bioactive glasses and their properties. The addition of small quantities of Ce to the silicate bioglass favours the depolymerisation of the silicate network with a positive effect on the ability to dissolve in body fluid. Moreover, the under coordination of both the Ce3+ and Ce4+ species in these glasses enhances their catalytic activity towards hydrogen peroxide. Conversely, the formation of cerium phosphate domains in the phosphosilicate glasses leads to detrimental effects for both the solubility and the catalytic activity of the glasses. Finally, a new quantitative view of the structure-activity relationships governing the macroscopic properties of these glasses has been obtained by means of structural descriptor that takes into account the fragmentation of the Si network and the consequent rearrangement of the modifier ions and the network destruction per cerium unit descriptor.

New Insight into Mixing Fluoride and Chloride in Bioactive Silicate Glasses

Adding fluoride into bioactive glasses leads to fluorapatite formation and a decrease in glass transition temperature. Recently, chloride has been introduced into glasses as an alternative to fluoride. The presence of the large chloride ion lowers glass crystallisation tendency and increases glass molar volume, which effectively facilitates glass degradation and bone-bonding apatite-like layer formation. However, there is no information regarding the effect of mixing fluoride and chloride on the glass structure and properties. This study aims to synthesize mixed fluoride and chloride containing bioactive glasses; investigate the structural role of fluoride and chloride and their effects on glass properties. The chloride content measurements reveal that 77–90% of chloride was retained in these Q2 type glasses. Glass transition temperature reduced markedly with an increase in CaX2 (X = F + Cl) content, while the glass molar volume increased. 29Si MAS-NMR results show that the incorporation of mixed fluoride and chloride did not cause significant change in the polymerization of the silicate network and no detectable concentration of Si-F/Cl bands were present. This agrees with 19F NMR spectra showing that F existed as F-Ca(n) species.

Effect of strontium oxide (SrO) on the microstructure and bioactivity of melt derived bioactive silicate glass

Effect of strontium oxide (SrO) on the microstructure and bioactivity of melt derived bioactive silicate glass

Novel Antibacterial and Bioactive Silicate Glass Nanoparticles for Biomedical Applications

In this work, the authors propose a new quick sol–gel procedure for bioglass nanoparticles production containing 10% mol of silver (AgBGs). These new AgBGs are characterized by Zeta potential analysis, scanning electron microscopy with X‐ray microanalysis (SEM/EDS), X‐ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and microbiological tests to confirm their bioactive and antibacterial properties. SEM shows that the average particle size is less than 200 nm and EDS confirms the successful incorporation of Ag2O in the bioglass matrix. XRD confirms the amorphous nature of the AgBGs and, after SBF immersion, reveals their bioactive behavior with the presence of crystalline phase of calcium silicate and phosphorus oxide, which are also detected by FTIR analysis. FTIR also confirms the formation of typical siloxane bonds resulting from the condensation of silicate glass. Lastly, it is found that the developed AgBGs has an antibacterial effect against two different types of bacteria, thus demonstrating their ability to reduce the bacterial infection within 16 h.

Influence of dissolution products of a novel Ca-enriched silicate bioactive glass-ceramic on VEGF release from bone marrow stromal cells

AbstractThis study evaluated the influence of ionic dissolution products of a novel Ca-enriched silicate bioactive glass compared to commercial available hydroxyapaptite samples (Endobonr) on cell activity and vascular endothelial growth factor (VEGF) release in vitro. Bone marrow stromal cells (ST-2) were cultivated with the supernatant of granules of different sizes and at different concentrations (0-1 wt/vol % of granules) for 48 h. In addition to in vitro studies, Ca-ion release from all as cell morphology observation revealed no cytotoxic effect of the released products from all tested materials. It was found that supernatants from granules in concentrations of 1 wt/vol %enhanced the VEGF release from ST2 cells, which is important as a marker of the vascularisation ability of the glass during the bone healing process.

Synthesis, characterization and in vitro bioactivity of mesoporous copper silicate bioactive glasses

In this study, 68SiO2–23CaO–4P2O5–CuO bioglasses with and without surfactant (nonionic block copolymer, EO20PO70EO20 P123) for producing multifunctional scaffold were synthesized by sol-gel method. The resulting dried sol underwent an evaporation-induced self-assembly (EISA) process at 40°C. TG-DTA (thermogravimetric-differential thermal analysis) was completed to obtain the optimized temperature for calcination of the prepared powder. The dried gel was calcined at 650°C for 2h to obtain the final bioglasses. Then, the composition and phase structure, morphology, surface area and mesoporous structure were evaluated by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET) analyses. In addition, the biological behavior (bioactivity, biocompatibility and antibacterial properties) of the powder was examined for their applicability in medical science. The results demonstrated that the synthesized bioglass powder formed mesoporous structure with nano-sized morphology and high surface area, and also suitable biological characteristics. The P123 (the nonionic block copolymer EO20PO70EO20) surfactant was responsible for improving homogeneous mesoporous structures and biological characteristics for the template bioglass. In addition, the use of copper in the glass structure did not inhibit its anti-bacterial properties and resulted in a low risk toxic bioglass. Finally, this synthesized bioactive glass could have the potential capability for bone defects treatment in tissue engineering due to their versatile attributes.

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

AbstractBioactive 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.

Development and characterization of niobium-releasing silicate bioactive glasses for tissue engineering applications

Novel niobium-containing bioactive glass formulations (Nb-BGs) were designed, produced and used to fabricate sintered glass-ceramic granules to examine their in vitro bioactivity and angiogenic potential. Nb-BGs were prepared by melting and quenching. Afterwards, the glasses were crushed and milled into fine powders. These powders were used to make aqueous slurries which were poured into molds, dried and sintered to produce pellets, from which granules of 0.5–0.85mm in size were obtained. In vitro bioactivity was tested by immersing the granules in simulated body fluid for up to 14days. Cell biology tests were carried out by indirect culture of bone marrow stromal cells (ST-2) with supernatants resulting from incubation of BG granules in cell culture medium. The effect of dissolution products from Nb-BGs on the secretion of vascular endothelial growth factor (VEGF) was assessed to characterize the angiogenic potential of the new Nb-containing BG compositions.

Modeling the Onset of Phase Separation in CaO-SiO2-CaCl2 Chlorine-Containing Silicate Glasses.

The addition of chlorine into a bioactive glass composition is expected to reduce its abrasiveness and increase its bioactivity, which is important for dental applications such as toothpastes. There is a lack of information and understanding regarding the structural role of chlorine in chlorine-containing bioactive silicate glasses. This has prompted classical core-shell model molecular dynamics simulations of (50 - x/2)CaO-(50 - x/2)SiO2-xCaCl2 glasses to be performed, where x ranges from x = 0.0 to 43.1 mol % CaCl2. These ternary glasses are advantageous for a fundamental study because they do not have additional network formers (e.g., phosphorus pentoxide) or modifiers (e.g., sodium) typically found in bioactive glass compositions. The (50 - x/2)CaO-(50 - x/2)SiO2-xCaCl2 glasses were seen to become phase-separated around the x = 16.1 mol % CaCl2 composition, and chlorine predominantly coordinated with calcium. These findings provide a solid foundation for further computational modeling work on more complex chlorine-containing bioactive glass compositions.

* Substituted Borosilicate Glasses with Improved Osteogenic Capacity for Bone Tissue Engineering.

Borosilicate bioactive glasses (BBGs) have shown the capacity to promote higher formation of new bone when compared with silicate bioactive glasses. Herein, we assessed the capacity of BBGs to induce osteogenic differentiation of bone marrow mesenchymal stem cells (BM-MSCs) as a function of their substituted divalent cations (Mg2+, Ca2+, Sr2+). To this purpose, we synthesized BBG particles by melt quenching. The cell viability, proliferation, and morphology (i.e., PrestoBlue®, PicoGreen®, and DAPI and Phalloidin stainings, respectively), as well as protein expression (i.e., alkaline phosphatase, ALP; osteopontin, OP; and osteocalcin, OC), of BM-MSCs in contact with BBGs were evaluated for 21 days. We observed an enhanced expression of bone-specific proteins (ALP, OP, and OC) and high mineralization of BM-MSCs under BBG-Mg and BBG-Sr-conditioned osteogenic media for concentrations of 20 and 50 mg/mL with low cytotoxic effects. Moreover, BBG-Sr, at a concentration of 50 mg/mL, was able to increase the mineralization and expression of the same bone-specific proteins even under basal medium conditions. These results indicated that the proposed BBGs improved osteogenic differentiation of BM-MSCs, therefore showing their potential as relevant biomaterials for bone tissue regeneration, not only by bonding to bone tissue but also by stimulating new bone formation.

Crystallization and sintering of borosilicate bioactive glasses for application in tissue engineering.

Typical silicate bioactive glasses are known to crystallize readily during the processing of porous scaffolds. While such crystallization does not fully suppress the bioactivity, the presence of significantly large amounts of crystals leads to a decrease in the rate of reaction of the glass and an uncontrolled release of ions. Furthermore, due to the non-congruent dissolution of silicate glasses, these materials have been shown to remain within the surgical site even 14 years post-operation. Therefore, bioactive materials that can dissolve more effectively and have higher conversion rates are required. Within this work, boron was introduced, in the FDA approved S53P4 glass, at the expense of SiO2. The crystallization and sintering-ability of the newly developed glasses were investigated by differential thermal analysis. All the glasses were found to crystallize primarily from the surface, and the crystal phase precipitation was dependent on the quantity of B2O3 incorporated. The rate of crystallization was found to be lower for the glasses when 25, 50 and 75% of SiO2 was replaced with B2O3. These glasses were further sintered into porous scaffolds using simple heat sintering. The impact of glass particle size and heat treatment temperature on the scaffold porosity and average pore size was investigated. Scaffolds with porosity ranging from 10 to 60% and compressive strength ranging from 1 to 35 MPa were produced. The scaffolds remained amorphous during processing and their ability to rapidly precipitate hydroxycarbonate apatite was maintained. This is of particular interest in the field of tissue engineering as scaffold degradation and reaction is generally faster and offers higher controllability as opposed to the current partially/fully crystallized scaffolds obtained from the FDA approved bioactive glasses.

Characterization of Some Bioactive Glasses and Glass-ceramics Prepared by a Hydrothermal Method

Powders of different samples of bioactive silicate glass ceramics were prepared by a hydrothermal method (HTM). The thermal energy assisted method was applied as an alternative to ultrasonic and microwave energy radiation assisted tools. Characterization of the glasses was carried out by FTIR (Fourier transform infrared) absorption spectroscopy. The different crystalline phases and crystallographic parameters were explored using X-ray diffraction (XRD) analysis. Differential scanning calorimetry and thermogravimetric analysis were carried out to investigate the thermal characteristics of the prepared samples. Transmission electron microscopy (TEM) and electron diffraction patterns (EDP) were performed to examine the internal microstructure of the bioactive glass samples. The hydrothermal assisted method is an appropriate technique to carry out the reaction in a short time. In addition, this method can modify the reaction environment to produce amorphous glassy materials after just a short time of thermal treatment. The sintered glass-ceramic materials prepared by such technique are characterized with fine size and more crystallized structure than those prepared by the conventional melting method. Fine structure leads to an increase in surface area which in turn participates to a great extent in improving compatibility and bioactivity of the materials.

Creation of bioactive glass (13–93) scaffolds for structural bone repair using a combined finite element modeling and rapid prototyping approach

There is a clinical need for synthetic bioactive materials that can reliably repair intercalary skeletal tissue loss in load-bearing bones. Bioactive glasses have been investigated as one such material but their mechanical response has been a concern. Previously, we created bioactive silicate glass (13–93) scaffolds with a uniform grid-like microstructure which showed a compressive strength comparable to human cortical bone but a much lower flexural strength. In the present study, finite element modeling (FEM) was used to re-design the scaffold microstructure to improve its flexural strength without significantly lowering its compressive strength and ability to support bone infiltration in vivo. Then scaffolds with the requisite microstructures were created by a robotic deposition method and tested in four-point bending and compression to validate the FEM simulations. In general, the data validated the predictions of the FEM simulations. Scaffolds with a porosity gradient, composed of a less porous outer region and a more porous inner region, showed a flexural strength (34±5MPa) that was more than twice the value for the uniform grid-like microstructure (15±5MPa) and a higher compressive strength (88±20MPa) than the grid-like microstructure (72±10MPa). Upon implantation of the scaffolds for 12weeks in rat calvarial defects in vivo, the amount of new bone that infiltrated the pore space of the scaffolds with the porosity gradient (37±16%) was similar to that for the grid-like scaffolds (35±6%). These scaffolds with a porosity gradient that better mimics the microstructure of human long bone could provide more reliable implants for structural bone repair.