Influence of strontium and the importance of glass chemistry and structure when designing bioactive glasses for bone regeneration

Bone regeneration in sheep model induced by strontium-containing mesoporous bioactive glasses

Local delivery of therapeutic ions from bioactive mesoporous glasses (MBGs) is postulated as one of the most promising strategies for regenerative therapy of critical bone defects. Among these ions, Sr2+ cation has been widely considered for this purpose as part of the composition of MBGs. MBGs of chemical composition 75SiO2-25-x CaO-5P2O5-xSrO with x = 0, 2.5 and 5 (% mol) were prepared by the evaporation induced self-assembly (EISA) method. Strontium incorporation did not affect the apatite forming ability of Sr-free MBG when these bioceramics are treated with simulated body fluid (SBF). In vitro cell viability showed that proliferation of MC3T3-E1 preosteoblast is not affected by the presence of Sr2+ cations, whereas ALP activity and gene expression of Runx2, ALP and VEGF is increased as a function of Sr content. Besides, cell proliferation and VEGF expression of HUVEC cells were also increased with the Sr2+ content. In this work, we present for the first time the effects of Sr containing MBGs on bone regeneration in a large animal model (sheep), after implantation in a cavitary defect. The histomorphometrical analysis and immunohistochemistry indicate that the incorporation of Sr2+ ion greatly enhances the osteoregenerating potential of MBGs. In this sense, the measured ossification areas were 7 % and 20 % for MBG and Sr-MBG, respectively. Besides, the thickness of the newly formed trabeculae was 15 μm and 30 μm for MBG and Sr-MBG, respectively. This enhancement of Sr2+ mediated bone formation would be justified by the transient osteoclastogenesis inhibition and the osteogenesis-angiogenesis increase due to the endothelial cell proliferation and increased vascular endothelial growth factor expression.

Glasses for bone regeneration: structural features controlling physical properties and ion release of bioactive glasses 45S5, S53P4 and 13-93

The structure, i.e. atomic arrangement, of glasses is known to determine many of their properties. This study investigates the structure of three well-known bioactive glass compositions, 45S5 (known as Bioglass), S53P4 (commercialised as BonAlive) and 13-93 (developed for improved high-temperature processing) by Si-29 and P-31 solid-state nuclear magnetic resonance and Raman spectroscopy. Results show that 45S5 has a more depolymerised silicate structure than the other two glasses, in agreement with its lowest silica content. These structural differences explain the well known high solubility and fast reactivity in vivo of 45S5 compared to the other two compositions. Differences between S53P4 and 13-93, by contrast, originate more from differences in their average modifier field strength, as their network connectivity, i.e. average silicate network polymerisation, is similar. As a result, 13-93 shows the lowest crystallisation tendency of the three glasses but also reacts relatively slowly during contact with aqueous solutions. The structural differences are also reflected in glass viscosity, where at a given temperature 45S5 has the lowest viscosity, 13-93 the highest and S53P4's viscosity is lying in between.

A new approach to overcome cytotoxic effects of Cu by delivering dual therapeutic ions (Sr, Cu)

INTRODUCTION

The incorporation of trace elements such as strontium (Sr) and copper (Cu) in the composition of mesoporous bioactive glass (MBG) is widely known to enhance its biological functionality for bone tissue regeneration METHODS: Two MBG powders with the composition 80SiO2-11CaO-5P2O5-xCuO/SrO, one doped with 4 mol.% of CuO, the second with 4 mol.% of SrO were blended in the weight ratios of Cu-MBG: Sr-MBG; 100:0, 70: 30, 50: 50, 30: 70 and 0:100 aiming at minimizing Cu to minimize the cytotoxicity of Cu while preserving its antimicrobial activity. The synergistic effects of Sr and Cu ions on bioactivity, cytotoxicity, and antimicrobial activity were studied.

RESULTS

Transmission electron microscopy (TEM) examination of Cu-MBG and Sr-MBG showed fringes related to the development of a mesoporous structure. The specific surface area values of the Cu-MBG and Sr-MBG powders were 287 and 349 m2/g, respectively. A characteristic compact layer consisting of particles with platelet-like morphology commonly associated with HAp crystals was confirmed after 7 days soaking in simulated body fluid (SBF). Mouse preosteoblast cells (MC3T3-E1) exhibited higher cell viability when exposed to a 1 % w/v eluate from blended Cu-MBG powders compared to pure Cu-MBG. Notably, the Cu-MBG: Sr-MBG ratio of 30:70 exhibited cell viability of around 85 % at this concentration. A higher cell viability (above 100 %) towards MC3T3-E1 cells was observed for all powders when tested with the 0.1 % w/v eluate. With progressive increase in the amount of Cu-MBG in the blended system the bacterial inhibitory effects were more pronounced. The Cu ions released from Cu-MBG generate hydroxyl ions and increase the pH leading to disruption of the cellular membrane of microbes, resulting in enhanced antimicrobial activity.

CONCLUSION

This newly developed blended system composed of Cu and Sr doped MBGs is expected to be more effective as bioactive filler in comparison to single ion doped MBGs for bone tissue engineering applications.

An Enhanced Bioactive Glass Composition with Improved Thermal Stability and Sinterability

The development of new bioactive glasses (BGs) with enhanced bioactivity and improved resistance to crystallization is crucial for overcoming the main challenges faced by commercial BGs. Most shaping processes require thermal treatments, which can induce partial crystallization, negatively impacting the biological and mechanical properties of the final product. In this study, we present a novel bioactive glass composition, S53P4_MSK, produced by a melt-quench route. This novel composition includes magnesium and strontium, known for their therapeutic effects, and potassium, recognized for improving the thermal properties of bioactive glasses. The thermal properties were investigated through differential thermal analysis, heating microscopy and sintering tests from 600 °C to 900 °C. These characterizations, combined with X-ray diffraction analysis, demonstrated the high sinterability without crystallization of S53P4_MSK, effectively mitigating related issues. The mechanical properties-elastic modulus, hardness and fracture toughness-were evaluated on the sintered sample by micro-indentation, showing high elastic modulus and hardness. The bioactivity of the novel BG was assessed following Kokubo's protocol and confirmed by scanning electron microscopy, X-ray energy dispersive spectroscopy, and Raman spectroscopy. The novel bioactive glass composition has shown high sinterability without crystallization at 700 °C, along with good mechanical properties and bioactivity.

Structural and Dynamical Effects of the CaO/SrO Substitution in Bioactive Glasses

Silicate glasses containing silicon, sodium, phosphorous, and calcium have the ability to promote bone regeneration and biodegrade as new tissue is generated. Recently, it has been suggested that adding SrO can benefit tissue growth and silicate glass dissolution. Motivated by these recent developments, the effect of SrO/CaO-CaO/SrO substitution on the local structure and dynamics of Si-Na-P-Ca-O oxide glasses has been studied in this work. Differential thermal analysis has been performed to determine the thermal stability of the glasses after the addition of strontium. The local structure has been studied by neutron diffraction augmented by Reverse Monte Carlo simulation, and the local dynamics by neutron Compton scattering and Raman spectroscopy. Differential thermal analysis has shown that SrO-containing glasses have lower glass transition, melting, and crystallisation temperatures. Moreover, the addition of the Sr2+ ions decreased the thermal stability of the glass structure. The total neutron diffraction augmented by the RMC simulation revealed that Sr played a similar role as Ca in the glass structure when substituted on a molar basis. The bond length and the coordination number distributions of the network modifiers and network formers did not change when SrO (x = 0.125, 0.25) was substituted for CaO (25-x). However, the network connectivity increased in glass with 12.5 mol% CaO due to the increased length of the Si-O-Si interconnected chain. The analysis of Raman spectra revealed that substituting CaO with SrO in the glass structure dramatically enhances the intensity of the high-frequency band of 1110-2000 cm-1. For all glasses under investigation, the changes in the relative intensities of Raman bands and the distributions of the bond lengths and coordination numbers upon the SrO substitution were correlated with the values of the widths of nuclear momentum distributions of Si, Na, P, Ca, O, and Sr. The widths of nuclear momentum distributions were observed to soften compared to the values observed and simulated in their parent metal-oxide crystals. The widths of nuclear momentum distributions, obtained from fitting the experimental data to neutron Compton spectra, were related to the amount of disorder of effective force constants acting on individual atomic species in the glasses.

Two decades of continuous progresses and breakthroughs in the field of bioactive ceramics and glasses driven by CICECO-hub scientists

Over the past two decades, the CICECO-hub scientists have devoted substantial efforts to advancing bioactive inorganic materials based on calcium phosphates and alkali-free bioactive glasses. A key focus has been the deliberate incorporation of therapeutic ions like Mg, Sr, Zn, Mn, or Ga to enhance osteointegration and vascularization, confer antioxidant properties, and impart antimicrobial effects, marking significant contributions to the field of biomaterials and bone tissue engineering. Such an approach is expected to circumvent the uncertainties posed by methods relying on growth factors, such as bone morphogenetic proteins, parathyroid hormone, and platelet-rich plasma, along with their associated high costs and potential adverse side effects. This comprehensive overview of CICECO-hub's significant contributions to the forefront inorganic biomaterials across all research aspects and dimensionalities (powders, granules, thin films, bulk materials, and porous structures), follows a unified approach rooted in a cohesive conceptual framework, including synthesis, characterization, and testing protocols. Tangible outcomes [injectable cements, durable implant coatings, and bone graft substitutes (scaffolds) featuring customized porous architectures for implant fixation, osteointegration, accelerated bone regeneration in critical-sized bone defects] were achieved. The manuscript showcases specific biofunctional examples of successful biomedical applications and effective translations to the market of bone grafts for advanced therapies.

In vitroassessment of a gallium-doped glass polyalkenoate cement: chemotherapeutic potential, cytotoxicity and osteogenic effects

Metastatic bone lesions are often osteolytic, which causes advanced-stage cancer sufferers to experience severe pain and an increased risk of developing a pathological fracture. Gallium (Ga) ion possesses antineoplastic and anti-bone resorption properties, suggesting the potential for its local administration to impede the growth of metastatic bone lesions. This study investigated the chemotherapeutic potential, cytotoxicity, and osteogenic effects of a Ga-doped glass polyalkenoate cement (GPC) (C-TA2) compared to its non-gallium (C-TA0) counterpart. Ion release profiles revealed a biphasic pattern characterized by an initial burst followed by a gradually declining release of ions. C-TA2 continued to release Ga steadily throughout the experimentation period (7 d) and exhibited prolonged zinc (Zn) release compared to C-TA0. Interestingly, the Zn release from both GPCs appeared to cause a chemotherapeutic effect against H1092 lung cancer cellsin vitro, with the prolonged Zn release from C-TA2 extending this effect. Unfortunately, both GPCs enhanced the viability of HCC2218 breast cancer cells, suggesting that the chemotherapeutic effects of Zn could be tied to cellular differences in preferred Zn concentrations. The utilization of SAOS-2 and MC3T3 cell lines as bone cell models yielded conflicting results, with the substantial decline in MC3T3 viability closely associated with silicon (Si) release, indicating cellular variations in Si toxicity. Despite this ambiguity, both GPCs exhibited harmful effects on the osteogenesis of primary rat osteoblasts, raising concerns about excessive burst Zn release. While Ga/Zn-doped GPCs hold promise for treating metastatic bone lesions caused by lung cancers, further optimization is required to mitigate cytotoxicity on healthy bone.

The unexplored role of alkali and alkaline earth elements (ALAEs) on the structure, processing, and biological effects of bioactive glasses

Bioactive glass has been employed in several medical applications since its inception in 1969. The compositions of these materials have been investigated extensively with emphasis on glass network formers, therapeutic transition metals, and glass network modifiers. Through these experiments, several commercial and experimental compositions have been developed with varying chemical durability, induced physiological responses, and hydroxyapatite forming abilities. In many of these studies, the concentrations of each alkali and alkaline earth element have been altered to monitor changes in structure and biological response. This review aims to discuss the impact of each alkali and alkaline earth element on the structure, processing, and biological effects of bioactive glass. We explore critical questions regarding these elements from both a glass science and biological perspective. Should elements with little biological impact be included? Are alkali free bioactive glasses more promising for greater biological responses? Does this mixed alkali effect show increased degradation rates and should it be employed for optimized dissolution? Each of these questions along with others are evaluated comprehensively and discussed in the final section where guidance for compositional design is provided.

Effect of Strontium-Substituted Calcium Phosphate Coatings Prepared by One-Step Electrodeposition at Different Temperatures on Corrosion Resistance and Biocompatibility of AZ31 Magnesium Alloys

As potential degradable biomaterials, magnesium (Mg) alloys have development prospects in the field of orthopedic load-bearing, whereas the clinical application has encountered a bottleneck due to a series of problems caused by its rapid corrosion. In this study, strontium-substituted calcium phosphate (CaP) coatings with different structures were prepared on the surface of the Mg matrix by a simple one-step electrodeposition method at different temperatures, which enhanced the poor corrosion resistance of the Mg matrix. The coated sample prepared at 65 °C reduced the corrosion current density by 3 orders of magnitude and increased the impedance by nearly 2 orders of magnitude compared with bare Mg alloy, thanks to its dense fibrous structure similar to that of natural bones. Although the coating composition varies with different preparation temperatures, CaP, as an inorganic component similar to natural bone, has good cytocompatibility. Doping the right amount of strontium, which is a trace element in human bones, is beneficial to stimulate osteoblast differentiation, inhibit the activity of osteoclasts, and induce the formation of bone tissues. This provides a new option for modifying the Mg alloy with CaP coatings as a base.

Influence of Strontium on the Biological Behavior of Bioactive Glasses for Bone Regeneration

Bioactive glasses (BGs) can potentially be applied in biomedicine, mainly for bone repair and replacement, given their unique ability to connect to natural bone tissue and stimulate bone regeneration. Since their discovery, several glass compositions have been developed to improve the properties and clinical abilities of traditional bioactive glass. Different inorganic ions, such as strontium (Sr2+), have been incorporated in BG due to their ability to perform therapeutic functions. Sr2+ has been gaining prominence due to its ability to stimulate osteogenesis, providing an appropriate environment to improve bone regeneration, in addition to its antibacterial potential. However, as there are still points in the literature that are not well consolidated, such as the influence of ionic concentrations and the BG production technique, this review aims to collect information on the state of the art of the biological behavior of BGs containing Sr2+. It also aims to gather data on different types of BGs doped with different concentrations of Sr2+, and to highlight the manufacturing techniques used in order to analyze the influence of the incorporation of this ion for bone regeneration purposes.

Evaluation of biocomposite putty with strontium and zinc co-doped 45S5 bioactive glass and sodium hyaluronate

The application of powder or granule formed bioactive glasses in the defect area with the help of a liquid carrier to fill the defects is a subject of interest and is still open to development. In this study, it was aimed to prepare biocomposites of bioactive glasses incorporating different co-dopants with a carrier biopolymer and to create a fluidic material (Sr and Zn co-doped 45S5 bioactive glasses‑sodium hyaluronate). All biocomposite samples were pseudoplastic fluid type, which may be suitable for defect filling and had excellent bioactivity behaviors confirmed by FTIR, SEM-EDS and XRD. Biocomposites with Sr and Zn co-doped bioactive glass had higher bioactivity considering the crystallinity of hydroxyapatite formations compared to biocomposite with undoped bioactive glasses. Biocomposites with high bioactive glass content had hydroxyapatite formations with higher crystallinity compared to biocomposites with low bioactive glass. Furthermore, all biocomposite samples showed non-cytotoxic effect on the L929 cells up to a certain concentration. However, biocomposites with undoped bioactive glass showed cytotoxic effects at lower concentrations compared to biocomposites with co-doped bioactive glass. Thus, biocomposite putties utilizing Sr and Zn co-doped bioactive glasses may be advantageous for orthopedic applications due to their specified rheological, bioactivity, and biocompatibility properties.

Impact of silanization of different bioactive glasses in simplified adhesives on degree of conversion, dentin bonding and collagen remineralization

OBJECTIVE

To analyze simplified adhesive containing pure or silanized bioglass 45S5 (with calcium) or Sr-45S5 (strontium-substituted) fillers applied on dentin and to evaluate the microtensile bond strength (µTBS), interface nanoleakage, degree of conversion of adhesive, collagen degradation and remineralization.

METHODS

Ambar Universal adhesive (FGM) was doped with 10 wt% bioactive glasses to form following groups: Control (no bioglass), 45S5 (conventional bioglass 45S5), Sr-45S5 (Sr-substituted bioglass 45S5), Sil-45S5 (silanized bioglass 45S5) and Sil-Sr-45S5 (silanized bioglass Sr-45S5). Adhesives were applied after dentin acid-etching using phosphoric acid at extracted human molars. Resin-dentin sticks were obtained and tested for µTBS, nanoleakage at 24 h or 6 months. Degree of conversion was measured using micro-Raman spectroscopy. Dentin remineralization was assessed by FTIR after 6-month storage in PBS. Hydroxyproline (HYP) release was surveyed by UV-Vis spectroscopy. Statistical analysis was performed using ANOVA and Tukey's test (p < 0.05).

RESULTS

Regarding µTBS, Sr-45S5 and 45S5 presented higher and stable results (p > 0.05). Control (p = 0.018) and Sil-Sr-45S5 (p < 0.001) showed µTBS reduction after 6-month aging. Sil-Sr-45S5 showed higher HYP release than that obtained in the 45S5 group. Sil-45S5 showed mineral deposition and increase in µTBS (p = 0.028) after 6-months. All experimental adhesives exhibited higher degree of conversion compared to Control group, except for 45S5. All adhesives created gap-free interfaces, with very low silver impregnation, except for Sil-Sr-45S5.

SIGNIFICANCE

The incorporation of silanized 45S5 bioglass into the universal adhesive was advantageous in terms of dentin remineralization, bonding performance and adhesive polymerization. Conversely, Sil-Sr-45S5 compromised the µTBS, interface nanoleakage and had a negative impact on HYP outcomes.

Rapid Synthesis of Multifunctional Apatite via the Laser-Induced Hydrothermal Process

Synthetic biomaterials are used to overcome the limited quantity of human-derived biomaterials and to impart additional biofunctionality. Although numerous synthetic processes have been developed using various phases and methods, currently commonly used processes have some issues, such as a long process time and difficulties with extensive size control and high-concentration metal ion substitution to achieve additional functionality. Herein, we introduce a rapid synthesis method using a laser-induced hydrothermal process. Based on the thermal interaction between the laser pulses and titanium, which was used as a thermal reservoir, hydroxyapatite particles ranging from nanometer to micrometer scale could be synthesized in seconds. Further, this method enabled selective metal ion substitution into the apatite matrix with a controllable concentration. We calculated the maximum temperature achieved by laser irradiation at the surface of the thermal reservoir based on the validation of three simplification assumptions. Subsequent linear regression analysis showed that laser-induced hydrothermal synthesis follows an Arrhenius chemical reaction. Hydroxyapatite and Mg²⁺-, Sr²⁺-, and Zn²⁺-substituted apatite powders promoted bone cell attachment and proliferation ability due to ion release from the hydroxyapatite and the selective ion-substituted apatite powders, which had a low crystallinity and relatively high solubility. Laser-induced hydrothermal synthesis is expected to become a powerful ceramic material synthesis technology.

Crystallization effects on the photoluminescence efficiency of SrO-B2O3 glass activated by W6+, Eu3+, Dy3+ or Pr3+ ions

Binary strontium borate host glass together with samples doped with 0.25 %WO₃ and one of the rare - earth ions (0.125% Eu³⁺, Dy³⁺ or Pr³⁺) were prepared by conventional melting - annealing technique. DTA analysis of the host base glass was carried out to derive the proper temperatures which are necessary to convert glasses into their corresponding glass -ceramic through controlled thermal heat -treatment regime. Measurements of optical, FTIR, and PL spectra were carried out with special analysis of the spectral properties. The identity of glass - ceramic derivatives were investigated through x-ray diffraction, and TEM & SEM tools to identify their crystalline morphological features. The absorption spectrum of WO₃ - doped glass refers to the existence of dominant hexavalent tungsten ions. The RE- doped glass reveal characteristic visible - NIR absorption peaks due to the respective rare earth ions. FTIR spectra show absorption bands due to both triangular and tetravalent borate groups (BO₃, BO₄).PL spectra reveal excitation and emission characteristic peaks due to each specific rare earth ions. XRD indicate the preference of the host glass to form strontium pyroborate (SrB₄O₇) crystalline phase. This facilitates the clear knowledge of the crystallization behavior and hence can justify the effect of the crystallization on the studied properties.

Strontium Functionalization of Biomaterials for Bone Tissue Engineering Purposes: A Biological Point of View

Strontium (Sr) is a trace element taken with nutrition and found in bone in close connection to native hydroxyapatite. Sr is involved in a dual mechanism of coupling the stimulation of bone formation with the inhibition of bone resorption, as reported in the literature. Interest in studying Sr has increased in the last decades due to the development of strontium ranelate (SrRan), an orally active agent acting as an anti-osteoporosis drug. However, the use of SrRan was subjected to some limitations starting from 2014 due to its negative side effects on the cardiac safety of patients. In this scenario, an interesting perspective for the administration of Sr is the introduction of Sr ions in biomaterials for bone tissue engineering (BTE) applications. This strategy has attracted attention thanks to its positive effects on bone formation, alongside the reduction of osteoclast activity, proven by in vitro and in vivo studies. The purpose of this review is to go through the classes of biomaterials most commonly used in BTE and functionalized with Sr, i.e., calcium phosphate ceramics, bioactive glasses, metal-based materials, and polymers. The works discussed in this review were selected as representative for each type of the above-mentioned categories, and the biological evaluation in vitro and/or in vivo was the main criterion for selection. The encouraging results collected from the in vitro and in vivo biological evaluations are outlined to highlight the potential applications of materials’ functionalization with Sr as an osteopromoting dopant in BTE.

3D-printed composite, calcium silicate ceramic doped with CaSO4·2H2O: Degradation performance and biocompatibility

Calcium silicate is a common implant material with excellent mechanical strength and good biological activity. In recent years, the addition of strengthening materials to calcium silicate has been proven to promote bone tissue regeneration, but its degradation properties require further improvements. In this paper, calcium silicate was used as the matrix, and 10 wt% hydroxyapatite and 10 wt% strontium phosphate were added to im prove the biological activity of the scaffold. The effect of adding different amounts of calcium sulfate dihydrate (CaSO₄·2H₂O) on the degradation of the scaffold was explored. A porous ceramic scaffold was prepared by digital light processing (DLP) technology, and its performance was evaluated. Cell experiments showed that the addition of calcium sulfate improved cell proliferation and differentiation. Simulated body fluid (SBF) immersion tests showed that small amounts of apatite deposits appeared on the fourth day, larger deposits appeared on the 14th day, and degradation occurred on the surface after 28 days of immersion. Mechanical tests showed that the addition of 5 wt% CaSO₄·2H₂O improved the compressibility of the composite. After soaking in SBF for 14 days, it retained its compressive strength (11.8 MPa), which meets the requirements of cancellous bone, demonstrating its potential application value for bone repair.

Synthesis of an organic-inorganic hybrid with short organic molecular chains by sol-gel chemistry

An oligomer with short organic molecular chains was successfully synthesized with KH550 and KH560. This oligomer was combined with tetraethyl orthosilicate and calcium chloride to prepare an organic-inorganic hybrid biological material (OI-BM) by sol-gel chemistry. The hybrid was fully characterized by a series of instrumental characterizations including nuclear magnetic resonance spectrometry, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray energy spectroscopy and inductively coupled plasma spectrometry. OI-BM presented elastic deformation under compression. The elastic modulus and ultimate stress of OI-BM were 0.4 ± 0.1 GPa and 23.0 ± 4.0 MPa, respectively, lower than those of 45S5 bioactive glass (45S5-BG), whereas the strain at failure and modulus of toughness of OI-BM was about 4.5 times and 4 times higher. The hybrid is easy to form due to the improved mechanical property, suggesting excellent machining properties. The hybrid OI-BM produced hydroxyapatite in 1 h in simulated body fluid due to its excellent bioactivity. CCK-8 assay further demonstrated the desirable cytocompatibility of the hybrid. Thus, the hybrid can be a potential material for satisfying the mechanical property requirement of an implant.

How Surface Properties of Silica Nanoparticles Influence Structural, Microstructural and Biological Properties of Polymer Nanocomposites

The aim of this work was to study effect of the type of silica nanoparticles on the properties of nanocomposites for application in the guided bone regeneration (GBR). Two types of nanometric silica particles with different size, morphology and specific surface area (SSA) i.e., high specific surface silica (hss-SiO₂) and low specific surface silica (lss-SiO₂), were used as nano-fillers for a resorbable polymer matrix: poly(L-lactide-co-D,L-lactide), called PLDLA. It was shown that higher surface specific area and morphology (including pore size distribution) recorded for hss-SiO₂ influences chemical activity of the nanoparticle; in addition, hydroxyl groups appeared on the surface. The nanoparticle with 10 times lower specific surface area (lss-SiO₂) characterized lower chemical action. In addition, a lack of hydroxyl groups on the surface obstructed apatite nucleation (reduced zeta potential in comparison to hss-SiO₂), where an apatite layer appeared already after 48 h of incubation in the simulated body fluid (SBF), and no significant changes in crystallinity of PLDLA/lss-SiO₂ nanocomposite material in comparison to neat PLDLA foil were observed. The presence and type of inorganic particles in the PLDLA matrix influenced various physicochemical properties such as the wettability, and the roughness parameter note for PLDLA/lss-SiO₂ increased. The results of biological investigation show that the bioactive nanocomposites with hss-SiO₂ may stimulate osteoblast and fibroblast cells’proliferation and secretion of collagen type I. Additionally, both nanocomposites with the nanometric silica inducted differentiation of mesenchymal cells into osteoblasts at a proliferation stage in in vitro conditions. A higher concentration of alkaline phosphatase (ALP) was observed on the material modified with hss-SiO₂ silica.

In vivo behavior of bioactive glass-based composites in animal models for bone regeneration

This review presents the recent advances and the current state-of-the-art of bioactive glass-based composite biomaterials intended for bone regeneration. Composite materials comprise two (or more) constituents at the nanometre scale, in which typically, one constituent is organic and functions as the matrix phase and the other constituent is inorganic and behaves as the reinforcing phase. Such materials, thereby, more closely resemble natural bio-nanocomposites such as bone. Various glass compositions in combination with a wide range of natural and synthetic polymers have been evaluated in vivo under experimental conditions ranging from unloaded critical-sized defects to mechanically-loaded, weight-bearing sites with highly favourable outcomes. Additional possibilities include controlled release of anti-osteoporotic drugs, ions, antibiotics, pro-angiogenic substances and pro-osteogenic substances. Histological and morphological evaluations suggest the formation of new, highly vascularised bone that displays signs of remodelling over time. With the possibility to tailor the mechanical and chemical properties through careful selection of individual components, as well as the overall geometry (from mesoporous particles and micro-/nanospheres to 3D scaffolds and coatings) through innovative manufacturing processes, such biomaterials present exciting new avenues for bone repair and regeneration.

The use of bioactive glass (BAG) in dental composites: A critical review

OBJECTIVE

In recent years, numerous studies have analyzed the role of bioactive glass (BAG) as remineralizing additives in dental restorative composites. This current review provides a critical analysis of the existing literature, particularly focusing on BAGs prepared via the melt-quench route that form an "apatite-like" phase when immersed in physiological-like solutions.

METHODS

Online databases (Science Direct, PubMed and Google Scholar) were used to collect data published from 1962 to 2020. The research papers were analyzed and the relevant papers were selected for this review. Sol-gel BAGs were not included in this review since it is not a cost-effective manufacturing technique that can be upscaled and is difficult to incorporate fluoride.

RESULTS

BAGs release Ca²⁺, PO₄^3- and F^- ions, raise the pH and form apatite. There are numerous published papers on the bioactivity of BAGs, but the different glass compositions, volume fractions, particle sizes, immersion media, time points, and the characterization techniques used, make comparison difficult. Several papers only use certain characterization techniques that do not provide a full picture of the behavior of the glass. It was noted that in most studies, mechanical properties were measured on dry samples, which does not replicate the conditions in the oral environment. Therefore, it is recommended that samples should be immersed for longer time periods in physiological solutions to mimic clinical environments.

SIGNIFICANCE

BAGs present major benefits in dentistry, especially their capacity to form apatite, which could potentially fill any marginal gaps produced due to polymerization shrinkage.

A Review of Bioactive Glass/Natural Polymer Composites: State of the Art

Collagen, gelatin, silk fibroin, hyaluronic acid, chitosan, alginate, and cellulose are biocompatible and non-cytotoxic, being attractive natural polymers for medical devices for both soft and hard tissues. However, such natural polymers have low bioactivity and poor mechanical properties, which limit their applications. To tackle these drawbacks, collagen, gelatin, silk fibroin, hyaluronic acid, chitosan, alginate, and cellulose can be combined with bioactive glass (BG) nanoparticles and microparticles to produce composites. The incorporation of BGs improves the mechanical properties of the final system as well as its bioactivity and regenerative potential. Indeed, several studies have demonstrated that polymer/BG composites may improve angiogenesis, neo-vascularization, cells adhesion, and proliferation. This review presents the state of the art and future perspectives of collagen, gelatin, silk fibroin, hyaluronic acid, chitosan, alginate, and cellulose matrices combined with BG particles to develop composites such as scaffolds, injectable fillers, membranes, hydrogels, and coatings. Emphasis is devoted to the biological potentialities of these hybrid systems, which look rather promising toward a wide spectrum of applications.

Biomimetic and osteogenic 3D silk fibroin composite scaffolds with nano MgO and mineralized hydroxyapatite for bone regeneration

Artificial bioactive materials have received increasing attention worldwide in clinical orthopedics to repair bone defects that are caused by trauma, infections or tumors, especially dedicated to the multifunctional composite effect of materials. In this study, a weakly alkaline, biomimetic and osteogenic, three-dimensional composite scaffold (3DS) with hydroxyapatite (HAp) and nano magnesium oxide (MgO) embedded in fiber (F) of silkworm cocoon and silk fibroin (SF) is evaluated comprehensively for its bone repair potential in vivo and in vitro experiments, particularly focusing on the combined effect between HAp and MgO. Magnesium ions (Mg²⁺) has long been proven to promote bone tissue regeneration, and HAp is provided with osteoconductive properties. Interestingly, the weak alkaline microenvironment from MgO may also be crucial to promote Sprague-Dawley (SD) rat bone mesenchymal stem cells (BMSCs) proliferation, osteogenic differentiation and alkaline phosphatase (ALP) activities. This SF/F/HAp/nano MgO (SFFHM) 3DS with superior biocompatibility and biodegradability has better mechanical properties, BMSCs proliferation ability, osteogenic activity and differentiation potential compared with the scaffolds adding HAp or MgO alone or neither. Similarly, corresponding meaningful results are also demonstrated in a model of distal lateral femoral defect in SD rat. Therefore, we provide a promising 3D composite scaffold for promoting bone regeneration applications in bone tissue engineering.

The Use of Simulated Body Fluid (SBF) for Assessing Materials Bioactivity in the Context of Tissue Engineering: Review and Challenges

Some special implantable materials are defined as “bioactive” if they can bond to living bone, forming a tight and chemically-stable interface. This property, which is inherent to some glass compositions, or can be induced by applying appropriate surface treatments on otherwise bio-inert metals, can be evaluated in vitro by immersion studies in simulated body fluid (SBF), mimicking the composition of human plasma. As a result, apatite coating may form on the material surface, and the presence of this bone-like “biomimetic skin” is considered predictive of bone-bonding ability in vivo. This review article summarizes the story and evolution of in vitro bioactivity testing methods using SBF, highlighting the influence of testing parameters (e.g., formulation and circulation of the solution) and material-related parameters (e.g., composition, geometry, texture). Suggestions for future methodological refinements are also provided at the end of the paper.

Synthesis and characterization of novel calcium phosphate glass-derived cements for vital pulp therapy

Evaluation of the physicochemical behavior and setting reactions of a novel inorganic pulp capping cement which makes use of the unique corrosion properties of sodium metasilicate (NaSi) glass. NaSi and calcium phosphate (CaP) glass powders were synthesized through a melt-quench method. Cements were created by mixing various amounts of the glasses with deionized water at a powder-to-liquid ratio of 2.5 g mL^-1. Working and setting times were measured using the indentation standard ISO 9917-1. Sealing ability was tested by placing set samples of each composition in methylene blue dye solution for 24 h. Set samples were also submerged in phosphate buffered saline and incubated at 37 °C for one week. X-ray diffraction was used to identify mature crystalline phases after incubation. Infrared spectroscopy and scanning electron microscopy were used to characterize cements before and after setting and after incubation. Working and setting times measured in the ranges of 2-5 and 10-25 min, respectively. Working and setting time generally decrease with increased NaSi concentration. Cements with compositions of 25 and 33 wt% NaSi were found to resist the infiltration of dye and maintain their shape. Compositions outside this range absorbed dye and collapsed. Infrared spectroscopy provided insight into the setting mechanism of these cements. After one week in vitro, cements were found to contain crystalline phases matching chemically stable, bioactive phases. The combination of NaSi and CaP glasses has favorable setting behavior, sealing ability, and mature phases for pulp capping while relying on a relatively simple, inorganic composition.

Synthesis and characterization of osteoinductive visible light-activated adhesive composites with antimicrobial properties

Orthopedic surgical procedures based on the use of conventional biological graft tissues are often associated with serious post-operative complications such as immune rejection, bacterial infection, and poor osseointegration. Bioresorbable bone graft substitutes have emerged as attractive alternatives to conventional strategies because they can mimic the composition and mechanical properties of the native bone. Among these, bioactive glasses (BGs) hold great potential to be used as biomaterials for bone tissue engineering owing to their biomimetic composition and high biocompatibility and osteoinductivity. Here, we report the development of a novel composite biomaterial for bone tissue engineering based on the incorporation of a modified strontium- and lithium-doped 58S BG (i.e., BG-5/5) into gelatin methacryloyl (GelMA) hydrogels. We characterized the physicochemical properties of the BG formulation via different analytical techniques. Composite hydrogels were then prepared by directly adding BG-5/5 to the GelMA hydrogel precursor, followed by photocrosslinking of the polymeric network via visible light. We characterized the physical, mechanical, and adhesive properties of GelMA/BG-5/5 composites, as well as their in vitro cytocompatibility and osteoinductivity. In addition, we evaluated the antimicrobial properties of these composites in vitro, using a strain of methicillin-resistant Staphylococcus Aureus. GelMA/BG-5/5 composites combined the functional characteristics of the inorganic BG component, with the biocompatibility, biodegradability, and biomimetic composition of the hydrogel network. This novel biomaterial could be used for developing osteoinductive scaffolds or implant surface coatings with intrinsic antimicrobial properties and higher therapeutic efficacy.

Effect of solution condition on hydroxyapatite formation in evaluating bioactivity of B2O3 containing 45S5 bioactive glasses

The effects of testing solutions and conditions on hydroxyapatite (HAp) formation as a means of in vitro bioactivity evaluation of B2O3 containing 45S5 bioactive glasses were systematically investigated. Four glass samples prepared by the traditional melt and quench process, where SiO2 in 45S5 was gradually replaced by B2O3 (up to 30%), were studied. Two solutions: the simulated body fluid (SBF) and K2HPO4 solutions were used as the medium for evaluating in vitro bioactivity through the formation of HAp on glass surface as a function of time. It was found that addition of boron oxide delayed the HAp formation in both SBF and K2HPO4 solutions, while the reaction between glass and the K2HPO4 solution is much faster as compared to SBF. In addition to the composition and medium effects, we also studied whether the solution treatments (e.g., adjusting to maintain a pH of 7.4, refreshing solution at certain time interval, and no disturbance during immersion) affect HAp formation. Fourier transform infrared spectrometer (FTIR) equipped with an attenuated total reflection (ATR) sampling technique and scanning electron microscopy (SEM) were conducted to identify HAp formation on glass powder surfaces and to observe HAp morphologies, respectively. The results show that refreshing solution every 24 h produced the fastest HAp formation for low boron-containing samples when SBF was used as testing solution, while no significant differences were observed when K2HPO4 solution was used. This study thus suggests the testing solutions and conditions play an important role on the in vitro bioactivity testing results and should be carefully considered when study materials with varying bioactivities.

Bioactive glass coatings on metallic implants for biomedical applications

Metallic implant materials possess adequate mechanical properties such as strength, elastic modulus, and ductility for long term support and stability in vivo. Traditional metallic biomaterials, including stainless steels, cobalt-chromium alloys, and titanium and its alloys, have been the gold standards for load-bearing implant materials in hard tissue applications in the past decades. Biodegradable metals including iron, magnesium, and zinc have also emerged as novel biodegradable implant materials with different in vivo degradation rates. However, they do not possess good bioactivity and other biological functions. Bioactive glasses have been widely used as coating materials on the metallic implants to improve their integration with the host tissue and overall biological performances. The present review provides a detailed overview of the benefits and issues of metal alloys when used as biomedical implants and how they are improved by bioactive glass-based coatings for biomedical applications.

Strontium ion reinforced bioceramic scaffold for load bearing bone regeneration

Bone defects in load bearing areas require bone reconstruction with strong biomaterial having mechanical characteristics like cortical bone. Bioceramics are biomaterials that support bone formation as well as provide adequate mechanical properties. A strontium substitution of the bioceramic is expected to further increase its bioactivity by enhancing osteogenesis and protect the bone from osteoclastic resorption. The study involves development, characterization and in vivo testing of a newly developed strontium substituted hydroxyapatite based bioceramic scaffold (SrHAB) with sufficient biomechanical properties. Optimal concentration of strontium ion required for enhanced osteogenic differentiation was identified by comparing three compositions of SrHAB scaffold; namely Sr10HAB, Sr30HAB and Sr50 HAB for their Alkaline phosphatase activity in vitro. The selected Sr10HAB scaffold demonstrated in vivo bone formation with osteogenic differentiation of stromal derived mesenchymal stem cells (MSC) from human and ovine sources in ectopic and ovine models. Thus, Sr10HAB scaffold has a potential for application in load bearing bone requirements of orthopaedics and dentistry.

Multiple and Promising Applications of Strontium (Sr)-Containing Bioactive Glasses in Bone Tissue Engineering

Improving and accelerating bone repair still are partially unmet needs in bone regenerative therapies. In this regard, strontium (Sr)-containing bioactive glasses (BGs) are highly-promising materials to tackle this challenge. The positive impacts of Sr on the osteogenesis makes it routinely used in the form of strontium ranelate (SR) in the clinical setting, especially for patients suffering from osteoporosis. Therefore, a large number of silicate-, borate-, and phosphate-based BGs doped with Sr and produced in different shapes have been developed and characterized, in order to be used in the most advanced therapeutic strategies designed for the management of bone defects and injuries. Although the influence of Sr incorporation in the glass is debated regarding the obtained physicochemical and mechanical properties, the biological improvements have been found to be substantial both in vitro and in vivo. In the present study, we provide a comprehensive overview of Sr-containing glasses along with the current state of their clinical use. For this purpose, different types of Sr-doped BG systems are described, including composites, coatings and porous scaffolds, and their applications are discussed in the light of existing experimental data along with the significant challenges ahead.

Bioactive Glasses and Glass-Ceramics for Healthcare Applications in Bone Regeneration and Tissue Engineering

The discovery of bioactive glasses (BGs) in the late 1960s by Larry Hench et al. was driven by the need for implant materials with an ability to bond to living tissues, which were intended to replace inert metal and plastic implants that were not well tolerated by the body. Among a number of tested compositions, the one that later became designated by the well-known trademark of 45S5 Bioglass® excelled in its ability to bond to bone and soft tissues. Bonding to living tissues was mediated through the formation of an interfacial bone-like hydroxyapatite layer when the bioglass was put in contact with biological fluids in vivo. This feature represented a remarkable milestone, and has inspired many other investigations aiming at further exploring the in vitro and in vivo performances of this and other related BG compositions. This paradigmatic example of a target-oriented research is certainly one of the most valuable contributions that one can learn from Larry Hench. Such a goal-oriented approach needs to be continuously stimulated, aiming at finding out better performing materials to overcome the limitations of the existing ones, including the 45S5 Bioglass®. Its well-known that its main limitations include: (i) the high pH environment that is created by its high sodium content could turn it cytotoxic; (ii) and the poor sintering ability makes the fabrication of porous three-dimensional (3D) scaffolds difficult. All of these relevant features strongly depend on a number of interrelated factors that need to be well compromised. The selected chemical composition strongly determines the glass structure, the biocompatibility, the degradation rate, and the ease of processing (scaffolds fabrication and sintering). This manuscript presents a first general appraisal of the scientific output in the interrelated areas of bioactive glasses and glass-ceramics, scaffolds, implant coatings, and tissue engineering. Then, it gives an overview of the critical issues that need to be considered when developing bioactive glasses for healthcare applications. The aim is to provide knowledge-based tools towards guiding young researchers in the design of new bioactive glass compositions, taking into account the desired functional properties.

Additive Manufacturing for Guided Bone Regeneration: A Perspective for Alveolar Ridge Augmentation

Three-dimensional (3D) printing has become an important tool in the field of tissue engineering and its further development will lead to completely new clinical possibilities. The ability to create tissue scaffolds with controllable characteristics, such as internal architecture, porosity, and interconnectivity make it highly desirable in comparison to conventional techniques, which lack a defined structure and repeatability between scaffolds. Furthermore, 3D printing allows for the production of scaffolds with patient-specific dimensions using computer-aided design. The availability of commercially available 3D printed permanent implants is on the rise; however, there are yet to be any commercially available biodegradable/bioresorbable devices. This review will compare the main 3D printing techniques of: stereolithography; selective laser sintering; powder bed inkjet printing and extrusion printing; for the fabrication of biodegradable/bioresorbable bone tissue scaffolds; and, discuss their potential for dental applications, specifically augmentation of the alveolar ridge.

Structural, physico-mechanical and in-vitro bioactivity studies on SiO2-CaO-P2O5-SrO-Al2O3 bioactive glasses

Strontium based bioactive glasses have shown a better biocompatibility than calcia based bioactive glasses. In this report, we have shown that the bioactivity is found to be even more when we incorporate Al₂O₃ upto 1.5 mol% in SiO₂-CaO-P₂O₅-SrO bioactive glass. We have studied the structural, physico-mechanical and bioactive properties in these glasses with varying alumina concentration from 0.5 to 2.5 mol%. The bioactivity of the glasses is evaluated by in vitro test in simulated body fluid (SBF). The formation of hydroxy carbonated apatite layer (HCA) on the surface of glasses after immersion in SBF is identified by the XRD, FTIR and SEM. The substitution of Al₂O₃ for SrO in these glasses demonstrates a significant enhancement in compressive strength and elastic modulus. However cytotoxicity and cell viability assessed using human osteosarcoma U2-OS cell lines show the growth of the cells without causing any significant loss of viability and cell death upto 1.5 mol% addition of Al₂O₃. Osteosarcoma cells grow on the surface of bioglasses which make them biocompatible and fit for use in clinical trials.

Strontium-Doped Bioactive Glass Nanoparticles in Osteogenic Commitment

The present work has explored bioactive glass nanoparticles (BGNPs) and developed strontium-doped nanoparticles (BGNPsSr), envisioning orthopedic strategies compatible with vascularization. The nanoparticles were synthesized by the sol-gel method, achieving a diameter of 55 nm for BGNPs and 75 nm for BGNPsSr, and the inclusion of strontium caused no structural alteration. The nanoparticles exhibited high cytocompatibility for human umbilical vein endothelial cells (HUVECs) and SaOS-2. Additionally, the incorporation of strontium emphasized the tubule networking behavior of HUVECs. Our results demonstrate that the nanoparticle dissolution products encouraged the osteogenic differentiation of human adipose stem cells as it favored the expression of key genes and proteins associated with osteogenic lineage. This effect was markedly enhanced for BGNPsSr, which could prompt stem cell osteogenic differentiation without the typical osteogenic inducers. This study not only supports the hypothesis that BGNPs might play a significant role in osteogenic commitment but also highlights that the designed BGNPsSr is a valuable tool for stem cell "tune-up" in bone tissue engineering applications.

Bioactive Glasses: From Parent 45S5 Composition to Scaffold-Assisted Tissue-Healing Therapies

Nowadays, bioactive glasses (BGs) are mainly used to improve and support the healing process of osseous defects deriving from traumatic events, tumor removal, congenital pathologies, implant revisions, or infections. In the past, several approaches have been proposed in the replacement of extensive bone defects, each one with its own advantages and drawbacks. As a result, the need for synthetic bone grafts is still a remarkable clinical challenge since more than 1 million bone-graft surgical operations are annually performed worldwide. Moreover, recent studies show the effectiveness of BGs in the regeneration of soft tissues, too. Often, surgical criteria do not match the engineering ones and, thus, a compromise is required for getting closer to an ideal outcome in terms of good regeneration, mechanical support, and biocompatibility in contact with living tissues. The aim of the present review is providing a general overview of BGs, with particular reference to their use in clinics over the last decades and the latest synthesis/processing methods. Recent advances in the use of BGs in tissue engineering are outlined, where the use of porous scaffolds is gaining growing importance thanks to the new possibilities given by technological progress extended to both manufacturing processes and functionalization techniques.

Investigating the Effect of Glass Ion Release on the Cytocompatibility, Antibacterial Eflcacy and Antioxidant Activity of Y2O3 / CeO2 doped SiO2-SrO-Na2O glasses

The effect on ion release and cytocompatibility of Yttrium (Y) and Cerium (Ce) are investigated when substituted for Sodium (Na) in a 0.52SiO2-0.24SrO-0.24-Na2OMOglass series (where MO= Y2O3or CeO2). Glass leaching was evaluated through pH measurements and Inductive Coupled Plasma-Optical Emission Spectrometry (ICP-OES) analysiswhere the extract pH increased during incubation (11.2 - 12.5). Ion release of Silicon (Si), Na and Strontium (Sr) from the Con glass was at higher than that of glasses containing Y or Ce, and reached a limit after 1 day. Ion release from Y and Ce containing glasses reached a maximum of 1800 μg/mL, 1800 μg/mL, and 10 μg/mL for Si, Na, and Sr, respectively. Release of Y and Cewas below the ICP- OES detection limit <0.1 μg/mL. Cell viability of both L929 fibroblasts and MC3T3 osteoblasts decreased for Con, LY, and LCe extracts; HY extracts did not significantly decrease cell viability while YCe and HCe saw concentrationdependent viability decrease (20%, 33% extract concentrations). Bacterial studies saw Con and LCe eliminating >75% of bacteria at a 9% extract concentration. Antioxidant capacity (mechanism for neuroprotection) was evaluated using the ABTS assay. All glasses had inherent radical oxygen species (ROS) scavenging capability with Con reaching 9.5 mMTE.

In vitro osteogenesis by intracellular uptake of strontium containing bioactive glass nanoparticles

Monodispersed strontium containing bioactive glass nanoparticles (Sr-BGNPs) with two compositions were synthesised, through a modified sol-gel Stöber process, wherein silica nanoparticles (SiO₂-NPs) were formed prior to incorporation of calcium and strontium, with diameters of 90 ± 10 nm. The osteogenic response of a murine preosteoblast cell line, MC3T3-E1, was investigated in vitro for a nanoparticle concentration of 250 µg/mL with compositions of 87 mol% SiO₂, 7 mol% CaO, 6 mol% SrO and 83 mol% SiO₂, 3 mol% CaO, 14 mol% SrO. Dissolution studies in minimum essential media (α-MEM) at pH 7.4 and artificial lysosomal fluid (ALF) at pH 4.5 showed that the particles dissolved and that Sr²⁺ ions were released from Sr-BGNPs in both environments. Both particle compositions and their ionic dissolution products enhanced the alkaline phosphatase (ALP) activity of the cells and calcium deposition. Immunohistochemistry (IHC) staining of Col1a1, osteocalcin (OSC) and osteopontin (OSP) showed that these proteins were expressed in the MC3T3-E1 cells following three weeks of culture. In the basal condition, the late osteogenic differentiation markers, OSC and OSP, were more overtly expressed by cells cultured with Sr-BGNPs with 14 mol% SrO and their ionic release products than in the control condition. Col1a1 expression was only slightly enhanced in the basal condition, but was enhanced further by the osteogenic supplements. These data demonstrate that Sr-BGNPs accelerate mineralisation without osteogenic supplements. Sr-BGNPs were internalised into MC3T3-E1 cells by endocytosis and stimulated osteogenic differentiation of the pre-osteoblast cell line. Sr-BGNPs are likely to be beneficial for bone regeneration and the observed osteogenic effects of these particles can be attributed to their ionic release products.

STATEMENT OF SIGNIFICANCE

We report, for the first time, that monodispersed bioactive glass nanoparticles (∼90 nm) are internalised into preosteoblast cells by endocytosis but by unspecific mechanisms. The bioactive nanoparticles and their dissolution products (without the particles present) stimulated the expression of osteogenic markers from preosteoblast cells without the addition of other osteogenic supplements. Incorporating Sr into the bioactive glass nanoparticle composition, in addition to Ca, increased the total cation content (and therefore dissolution rate) of the nanoparticles, even though nominal total cation addition was constant, without changing size or morphology. Increasing Sr content in the nanoparticles and in their dissolution products enhanced osteogenesis in vitro. The particles therefore have great potential as an injectable therapeutic for bone regeneration, particularly in patients with osteoporosis, for which Sr is known to be therapeutic agent.

The synergistic effects of Sr and Si bioactive ions on osteogenesis, osteoclastogenesis and angiogenesis for osteoporotic bone regeneration

Bioactive ions released from bioceramics play important roles in bone regeneration; however, it is unclear how each ionic composition in complex bioceramics exerts its specific effect on bone regeneration. The aim of this study is to elucidate the functional effects of Sr and Si ions in bioceramics on the regeneration of osteoporotic bone. A model bioceramic with Sr- and Si-containing components (SMS) was successfully fabricated and the effects of ionic products from SMS bioceramics on the osteogenic, osteoclastic and angiogenic differentiation of rBMSCs-OVX and RANKL-induced osteoclasts were investigated. The results showed that SMS bioceramics could enhance ALP activity and expression of Col 1, OCN, Runx2, and angiogenic factors including VEGF and Ang-1. SMS bioceramics not only rebalanced the OPG/RANKL ratio of rBMSCs-OVX at early stage, but also repressed RANKL-induced osteoclast formation and expression of TRAP, DC-STAMP, V-ATPase a3, and NFATc1. The synergistic effects of Sr and Si ions were further investigated as compared with those of similar concentrations of Sr and Si ions alone. Sr and Si ions possessed synergistic effects on osteogenesis, osteoclastogenesis, and angiogenesis, attributed to the dominant effects of Sr ions on enhancing angiogenesis and repressing osteoclastogenesis, and the dominant effects of Si ions on stimulating osteogenesis. The in vivo study using critical-size mandibular defects of OVX rat models showed that SMS bioceramics could significantly enhance bone formation and mineralization compared with β-TCP bioceramics. Our results are the first to elucidate the specific effect of each ion from bioceramics on osteogenesis, osteoclastogenesis and angiogenesis for osteoporotic bone regeneration, paving the way for the design of functional biomaterials with complex compositions for tissue engineering and regenerative medicine.

STATEMENT OF SIGNIFICANCE

Bioactive ions released from bioceramics play important roles for bone regeneration; however, it is unclear how each of ionic compositions in complex bioceramics exerts its specific effect on bone regeneration. The aim of present study is to elucidate the functional effects of Sr and Si ions in complex bioceramics on the regeneration of osteoporotic bone. A model bioceramic with Sr and Si-containing components (SMS) was successfully fabricated and the effects of ionic products from SMS bioceramics on the osteogenic, osteoclastic and angiogenic differentiation of rBMSCs-OVX and RANKL-induced osteoclasts were investigated. The results showed that SMS bioceramics could enhance ALP activity and expression of Col 1, OCN, Runx2 and angiogenic factors including VEGF and Ang-1. SMS bioceramics not only rebalanced the ratio of OPG/RANKL of OVX-BMSCs at early stage, but also repressed RANKL-induced osteoclast formation and expression of TRAP, DC-STAMP, V-ATPase a3, and NFATc1. The synergistic effects of Sr and Si ions were further investigated as compared with the similar concentration of Sr and Si ions alone. It was found that Sr and Si ions possessed synergistic effects on osteogenesis, osteoclastogenesis and angiogenesis, attributed to the dominant effects of Sr ions on enhancing angiogenesis and repressing osteoclastogenesis, and the dominant effects of Si ions on stimulating osteogenesis. The in vivo study using critical-size mandibular defects of OVX rat models showed that SMS bioceramics could significantly enhance bone formation and mineralization as compared with β-TCP bioceramics. It is suggested that SMS bioceramics may be a promising biomaterial for osteoporotic bone regeneration. To our knowledge, this is the first time to elucidate the specific effect of each ion from bioceramics on osteogenesis, osteoclastogenesis and angiogenesis for osteoporotic bone regeneration, paving the way to design functional biomaterials with complex compositions for tissue engineering and regenerative medicine.

Highly degradable porous melt-derived bioactive glass foam scaffolds for bone regeneration

A challenge in using bioactive melt-derived glass in bone regeneration is to produce scaffolds with interconnected pores while maintaining the amorphous nature of the glass and its associated bioactivity. Here we introduce a method for creating porous melt-derived bioactive glass foam scaffolds with low silica content and report in vitro and preliminary in vivo data. The gel-cast foaming process was adapted, employing temperature controlled gelation of gelatin, rather than the in situ acrylic polymerisation used previously. To form a 3D construct from melt derived glasses, particles must be fused via thermal processing, termed sintering. The original Bioglass® 45S5 composition crystallises upon sintering, altering its bioactivity, due to the temperature difference between the glass transition temperature and the crystallisation onset being small. Here, we optimised and compared scaffolds from three glass compositions, ICIE16, PSrBG and 13-93, which were selected due to their widened sintering windows. Amorphous scaffolds with modal pore interconnect diameters between 100-150µm and porosities of 75% had compressive strengths of 3.4±0.3MPa, 8.4±0.8MPa and 15.3±1.8MPa, for ICIE16, PSrBG and 13-93 respectively. These porosities and compressive strength values are within the range of cancellous bone, and greater than previously reported foamed scaffolds. Dental pulp stem cells attached to the scaffold surfaces during in vitro culture and were viable. In vivo, the scaffolds were found to regenerate bone in a rabbit model according to X-ray micro tomography imaging.

STATEMENT OF SIGNIFICANCE

This manuscript describes a new method for making scaffolds from bioactive glasses using highly bioactive glass compositions. The glass compositions have lower silica content that those that have been previously made into amorphous scaffolds and they have been designed to have similar network connectivity to that of the original (and commercially used) 45S5 Bioglass. The aim was to match Bioglass' bioactivity. The scaffolds retain the amorphous nature of bioactive glass while having an open pore structure and compressive strength similar to porous bone (the original 45S5 Bioglass crystallises during sintering, which can cause reduced bioactivity or instability). The new scaffolds showed unexpectedly rapid bone regeneration in a rabbit model.