Bioactive Glass (BG) ICIE16 Shows Promising Osteogenic Properties Compared to Crystallized 45S5-BG

A comparative in vitro and in vivo analysis of the impact of copper substitution on the cytocompatibility, osteogenic, and angiogenic properties of a borosilicate bioactive glass

The 0106-B1-bioactive glass (BG) composition (in wt %: 37.5 SiO2, 22.6 CaO, 5.9 Na2O, 4.0 P2O5, 12.0 K2O, 5.5 MgO, and 12.5 B2O3) has demonstrated favorable processing properties and promising bone regeneration potential. The present study aimed to evaluate the biological effects of the incorporation of highly pro-angiogenic copper (Cu) in 0106-B1-BG in vitro using human bone marrow-derived mesenchymal stromal cells (BMSCs) as well as its in vivo potential for bone regeneration. CuO was added to 0106-B1-BG in exchange for CaO, resulting in Cu-doped BG compositions containing 1.0, 2.5 and 5.0 wt % CuO (composition in wt %: 37.5 SiO2, 21.6/ 20.1/17.6 CaO, 5.9 Na2O, 4.0 P2O5, 12.0 K2O, 5.5 MgO, 12.5 B2O3, and 1.0/ 2.5/ 5.0 CuO). In vitro, the BGs' impact on the viability, proliferation, and growth patterns of BMSCs was evaluated. Analyses of protein secretion, matrix formation, and gene expression were used for the assessment of the BGs' influence on BMSCs regarding osteogenic differentiation and angiogenic stimulation. The presence of Cu improved cytocompatibility, osteogenic differentiation, and angiogenic response when compared with unmodified 0106-B1-BG in vitro. In vivo, a critical-size femoral defect in rats was filled with scaffolds made from BGs. Bone regeneration was evaluated by micro-computed tomography. Histological analysis was performed to assess bone maturation and angiogenesis. In vivo effects regarding defect closure, presence of osteoclastic cells or vascular structures in the defect were not significantly changed by the addition of Cu compared with undoped 0106-B1-BG scaffolds. Hence, while the in vitro properties of the 0106-B1-BG were significantly improved by the incorporation of Cu, further evaluation of the BG composition is necessary to transfer these effects to an in vivo setting.

Ion Release and Apatite Formation of Resin Based Pit and Fissure Sealants Containing 45S5 Bioactive Glass

The purpose of this study was to evaluate a resin based pit and fissure sealant containing 45S5 bioactive glass (BAG) by examining its ion release, pH variation, and apatite-forming properties. To prepare the experimental materials, 45S5 BAG, used as a filler, was incorporated into the light curable resin matrix at concentrations of 0 (control), 12.5, 37.5, and 50.0 wt.%. Ion release, pH variation, and apatite formation (Raman spectrometer and scanning electron microscopy-energy-dispersive X-ray spectrometry measurements) were performed. While no ions were released from the control group, the experimental groups containing 45S5 BAG showed an increased release of Ca and P ions with increasing amounts of 45S5 BAG (p < 0.05). The pH of the experimental group remained high and was significantly different from the control group (p < 0.05). Unlike the control group, it was confirmed that the apatite peak was formed in the 50.0 wt.% BAG group for 90 days, and the apatite layer consisting of Ca and P was deposited on the surface. Thus, a resin based pit and fissure sealant containing 45S5 BAG is a promising material for preventing secondary caries by releasing ions and forming apatite.

Boric acid and Molybdenum trioxide synergistically stimulate osteogenic differentiation of human bone marrow-derived mesenchymal stromal cells

INTRODUCTION

Metals and their metal ions have been shown to exhibit certain biological functions that make them attractive for use in biomaterials, for example in bone tissue engineering (BTE) applications. Recent data shows that Molybdenum (Mo) is a potent inducer of osteogenic differentiation in human bone marrow-derived mesenchymal stromal cells (BMSCs). On the other hand, while boron (B) has been shown to enhance vascularization in BTE applications, its impact on osteogenic differentiation is volatile: while improved osteogenic differentiation has been described, other data show that B might slow down osteogenic differentiation or reduce the calcification of the extracellular matrix (ECM) when applied in higher doses. Still, the combination of pro-osteogenic Mo and pro-angiogenic B is certainly attractive in the context of biomaterials intended for the use in BTE.

METHODS

Therefore, the combined effect of molybdenum trioxide and boric acid at different ratios was investigated in this study to evaluate the effects on the viability, proliferation, osteogenic differentiation, ECM production and maturation of BMSCs.

RESULTS

Mo ions proved to be stronger osteoinductive compared to B, in fact, while some osteogenic differentiation markers were downregulated in the presence of B, the presence of Mo provided compensation. The combined application of B and Mo indicated a combination of individual effects, partially even enhancing the expected combined performance of the single stimulations.

CONCLUSIONS

The combination of B and Mo might be beneficial for BTE applications since the limited osteogenic properties of B can be compensated by Mo. Furthermore, since B is known to be pro-angiogenic, the combination of both substances may synergistically lead to improved vascularization and bone regeneration. Future studies should assess the angiogenic performance of this combination in greater detail.

Trends in bioactivity: inducing and detecting mineralization of regenerative polymeric scaffolds

Due to limitations of biological and alloplastic grafts, regenerative engineering has emerged as a promising alternative to treat bone defects. Bioactive polymeric scaffolds are an integral part of such an approach. Bioactivity importantly induces hydroxyapatite mineralization that promotes osteoinductivity and osseointegration with surrounding bone tissue. Strategies to confer bioactivity to polymeric scaffolds utilize bioceramic fillers, coatings and surface treatments, and additives. These approaches can also favorably impact mechanical and degradation properties. A variety of fabrication methods are utilized to prepare scaffolds with requisite morphological features. The bioactivity of scaffolds may be evaluated with a broad set of techniques, including in vitro (acellular and cellular) and in vivo methods. Herein, we highlight contemporary and emerging approaches to prepare and assess scaffold bioactivity, as well as existing challenges.

A comparative analysis of the cytocompatibility, protein adsorption, osteogenic and angiogenic properties of the 45S5- and S53P4-bioactive glass compositions

Despite their long history of application in orthopedics, the osteogenic and angiogenic properties as well as the cytocompatibility and protein adsorption of the 45S5- (in wt%: 45.0 SiO2, 24.5 Na2O, 24.5 CaO, 6.0 P2O5) and S53P4- (in wt%: 53.0 SiO2, 23.0 Na2O, 20.0 CaO, 4.0 P2O5) bioactive glass (BG) compositions have not yet been directly compared in one and the same experimental setting. In this study, the influence of morphologically equal granules of both BGs on proliferation, viability, osteogenic differentiation and angiogenic response of human bone-marrow-derived mesenchymal stromal cells (BMSCs) was assessed. Furthermore, their impact on vascular tube formation and adsorption of relevant proteins was evaluated. Both BGs showed excellent cytocompatibility and stimulated osteogenic differentiation of BMSCs. The 45S5-BG showed enhanced stimulation of bone morphogenic protein 2 (BMP2) gene expression and protein production compared to S53P4-BG. While gene expression and protein production of vascular endothelial growth factor (VEGF) were stimulated, both BGs had only limited influence on tubular network formation. 45S5-BG adsorbed a higher portion of proteins, namely BMP2 and VEGF, on its surface. In conclusion, both BGs show favorable properties with slight advantages for 45S5-BG. Since protein adsorption on BG surfaces is important for their biological performance, the composition of the proteome formed by osteogenic cells cultured on BGs should be analyzed in order to gain a deeper understanding of the mechanisms that are responsible for BG-mediated stimulation of osteogenic differentiation.

The Addition of Zinc to the ICIE16-Bioactive Glass Composition Enhances Osteogenic Differentiation and Matrix Formation of Human Bone Marrow-Derived Mesenchymal Stromal Cells

An ICIE16-bioactive glass (BG) composition (in mol%: 49.5 SiO2, 6.6 Na2O, 36.3 CaO, 1.1 P2O5, and 6.6 K2O) has demonstrated excellent in vitro cytocompatibility when cultured with human bone marrow-derived mesenchymal stromal cells (BMSCs). However, its impact on the development of an osseous extracellular matrix (ECM) is limited. Since zinc (Zn) is known to enhance ECM formation and maturation, two ICIE16-BG-based Zn-supplemented BG compositions, namely 1.5 Zn-BG and 3Zn-BG (in mol%: 49.5 SiO2, 6.6 Na2O, 34.8/33.3 CaO, 1.1 P2O5, 6.6 K2O, and 1.5/3.0 ZnO) were developed, and their influence on BMSC viability, osteogenic differentiation, and ECM formation was assessed. Compared to ICIE16-BG, the Zn-doped BGs showed improved cytocompatibility and significantly enhanced osteogenic differentiation. The expression level of the osteopontin gene was significantly higher in the presence of Zn-doped BGs. A larger increase in collagen production was observed when the BMSCs were exposed to the Zn-doped BGs compared to that of the ICIE16-BG. The calcification of the ECM was increased by all the BG compositions; however, calcification was significantly enhanced by the Zn-doped BGs in the early stages of cultivation. Zn constitutes an attractive addition to ICIE16-BG, since it improves its ability to build and calcify an ECM. Future studies should assess whether these positive properties remain in an in vivo environment.

Reduced Sodium Portions Favor Osteogenic Properties and Cytocompatibility of 45S5-Based Bioactive Glass Particles

Besides its favorable biological properties, the release of sodium (Na) from the well-known 45S5-bioactive glass (BG) composition (in mol%: 46.1, SiO2, 24.5 CaO, 24.5 Na2O, 6.0 P2O5) can hamper its cytocompatibility. In this study, particles of Na-reduced variants of 45S5-BG were produced in exchange for CaO and P2O5 via the sol-gel-route resulting in Na contents of 75%, 50%, 25% or 0% of the original composition. The release of ions from the BGs as well as their impact on the cell environment (pH values), viability and osteogenic differentiation (activity of alkaline phosphatase (ALP)), the expression of osteopontin and osteocalcin in human bone-marrow-derived mesenchymal stromal cells in correlation to the Na-content and ion release of the BGs was assessed. The release of Na-ions increased with increasing Na-content in the BGs. With decreasing Na content, the viability of cells incubated with the BGs increased. The Na-reduced BGs showed elevated ALP activity and a pro-osteogenic stimulation with accelerated osteopontin induction and a pronounced upregulation of osteocalcin. In conclusion, the reduction in Na-content enhances the cytocompatibility and improves the osteogenic properties of 45S5-BG, making the Na-reduced variants of 45S5-BG promising candidates for further experimental consideration.

A comparative in vitro and in vivo analysis of the biological properties of the 45S5-, 1393-, and 0106-B1-bioactive glass compositions using human bone marrow-derived stromal cells and a rodent critical size femoral defect model

Since the introduction of the 45S5-bioactive glass (BG), numerous new BG compositions have been developed. Compared to the 45S5-BG, 1393-BG shows favorable processing properties due to its low crystallization tendency and the 1393-BG-based borosilicate 0106-B1-BG exhibits improved angiogenic properties due to its boron content. Despite their close (chemical) relationship, the biological properties of the mentioned BG composition have not yet been comparatively examined. In this study, the effects of the BGs on proliferation, viability, osteogenic differentiation, and angiogenic factor production of human bone marrow-derived mesenchymal stromal cells were assessed. Scaffolds made of the BGs were introduced in a critical-sized femur defect model in rats in order to analyze their impact on bone defect regeneration. In vitro, 1393-BG and 0106-B1-BG outperformed 45S5-BG with regard to cell proliferation and viability. 1393-BG enhanced osteogenic differentiation; 0106-B1-BG promoted angiogenic factor production. In vivo, 0106-B1-BG and 45S5-BG outperformed 1393-BG in terms of angiogenic and osteoclastic response resulting in improved bone regeneration. In conclusion, the biological properties of BGs can be significantly modified by tuning their composition. Demonstrating favorable processing properties and an equally strong in vivo bone regeneration potential as 45S5-BG, 0106-B1-BG qualifies as a basis to incorporate other bioactive ions to improve its biological properties.

Effect of Thermal Treatments and Ion Substitution on Sintering and Crystallization of Bioactive Glasses: A Review

Bioactive glasses (BGs) are promising materials for bone regeneration due to their ability to bond with living bone tissue. However, thermal stability and mechanical properties of BGs need improvement for better clinical performance. In this paper, we present an overview of the influence of different ions on the sintering and crystallization of BGs. Specifically, this review focuses on the impact of thermal treatments on the crystallization of 45S5 and other significant BG compositions. Potential applications of these thermally treated BGs, such as scaffolds, BG-based composites, and thermally sprayed coatings, are explored. Moreover, the substitution of ions has been investigated as a method to enhance the thermal properties of BGs. Notably, zinc, potassium, and strontium have been studied extensively and have demonstrated promising effects on both the thermal and the mechanical properties of BGs. However, it is important to note that research on ion inclusion in BGs is still in its early stages, and further investigation is necessary to fully comprehend the effects of different ions on sintering and crystallization. Therefore, future studies should focus on optimizing the ion substitution method to improve the thermal, mechanical, and even biological properties of BGs, thereby enhancing their potential for various biomedical applications.

Bioglass obtained via one-pot synthesis as osseointegrative drug delivery system

Osseointegration is a fundamental process during which implantable biomaterial integrates with host bone tissue. The surgical procedure of biomaterial implantation is highly associated with the risk of bacterial infection. Thus, the research continues for biodegradable bone void fillers which are able to stimulate the bone tissue regeneration and locally deliver the antibacterial agent. Herein, we obtained bifunctional bioglass (BG) using novel, preoptimized, rapid one-pot synthesis. Following the ISO Standards, the influence of the obtained BG on osteoblast-mediated phenomena, such as osteoconduction and osteoinduction was assessed and compared to two commercial materials: bioactive glass powder 45S and bioactive glass powder 85S. Direct-contact tests revealed osteoblast adhesion to BG particles; whereas, tests on extracts confirmed high viability of cells incubated with BG extract. Analyses of gene expression, alkaline phosphatase activity, and calcium phosphates deposition confirmed the stimulation of early and late stages of osteoblast differentiation and mineralization. Additionally, an extended evaluation of intracellular calcium fluctuations revealed a possible correlation between osteoblast calcium uptake and extracellular matrix mineralization. Moreover, proposed bioglass exhibited satisfactory doxycycline adsorption capacity and release profile. The obtained results confirmed the bifunctionality of the proposed BG and indicated its potential as osseointegrative bone drug delivery system.

A review on borate bioactive glasses (BBG): effect of doping elements, degradation, and applications

Because of their excellent biologically active qualities, bioactive glasses (BGs) have been extensively used in the biomedical domain, leading to better tissue-implant interactions and promoting bone regeneration and wound healing. Aside from having attractive characteristics, BGs are appealing as a porous scaffold material. On the other hand, such porous scaffolds should enable tissue proliferation and integration with the natural bone and neighboring soft tissues and degrade at a rate that allows for new bone development while preventing bacterial colonization. Therefore, researchers have recently become interested in a different BG composition based on borate (B₂O₃) rather than silicate (SiO₂). Furthermore, apatite synthesis in the borate-based bioactive glass (BBG) is faster than in the silicate-based bioactive glass, which slowly transforms to hydroxyapatite. This low chemical durability of BBG indicates a fast degradation process, which has become a concern for their utilization in biological and biomedical applications. To address these shortcomings, glass network modifiers, active ions, and other materials can be combined with BBG to improve the bioactivity, mechanical, and regenerative properties, including its degradation potential. To this end, this review article will highlight the details of BBGs, including their structure, properties, and medical applications, such as bone regeneration, wound care, and dental/bone implant coatings. Furthermore, the mechanism of BBG surface reaction kinetics and the role of doping ions in controlling the low chemical durability of BBG and its effects on osteogenesis and angiogenesis will be outlined.

In vitro and in ovo impact of the ionic dissolution products of boron-doped bioactive silicate glasses on cell viability, osteogenesis and angiogenesis

Due to the pivotal role of angiogenesis in bone regeneration, the angiogenic properties of biomaterials are of high importance since they directly correlate with the biomaterials’ osteogenic potential via ‘angiogenic-osteogenic coupling’ mechanisms. The impact of bioactive glasses (BGs) on vascularization can be tailored by incorporation of biologically active ions such as boron (B). Based on the ICIE16-BG composition (in mol%: 49.5 SiO₂, 36.3 CaO, 6.6 Na₂O, 1.1 P₂O₅, 6.6 K₂O), three B-doped BGs have been developed (compositions in mol%: 46.5/45.5/41.5 SiO₂, 36.3 CaO, 6.6 Na₂O, 1.1 P₂O₅, 6.6 K₂O, 3/4/8 B₂O₃). The influence of B-doping on the viability, cellular osteogenic differentiation and expression of osteogenic and angiogenic marker genes of bone marrow-derived mesenchymal stromal cells (BMSCs) was analyzed by cultivating BMSCs in presence of the BGs’ ionic dissolution products (IDPs). Furthermore, the influence of the IDPs on angiogenesis was evaluated in ovo using a chorioallantoic membrane (CAM) assay. The influence of B-doped BGs on BMSC viability was dose-dependent, with higher B concentrations showing limited negative effects. B-doping led to a slight stimulation of osteogenesis and angiogenesis in vitro. In contrast to that, B-doping significantly enhanced vascularization in ovo, especially in higher concentrations. Differences between the results of the in vitro and in ovo part of this study might be explained via the different importance of vascularization in both settings. The implementation of new experimental models that cover the ‘angiogenic-osteogenic coupling’ mechanisms is highly relevant, for instance via extending the application of the CAM assay from solely angiogenic to angiogenic and osteogenic purposes.

In situ 4D tomography image analysis framework to follow sintering within 3D-printed glass scaffolds

We propose a novel image analysis framework to automate analysis of X-ray microtomography images of sintering ceramics and glasses, using open-source toolkits and machine learning. Additive manufacturing (AM) of glasses and ceramics usually requires sintering of green bodies. Sintering causes shrinkage, which presents a challenge for controlling the metrology of the final architecture. Therefore, being able to monitor sintering in 3D over time (termed 4D) is important when developing new porous ceramics or glasses. Synchrotron X-ray tomographic imaging allows in situ, real-time capture of the sintering process at both micro and macro scales using a furnace rig, facilitating 4D quantitative analysis of the process. The proposed image analysis framework is capable of tracking and quantifying the densification of glass or ceramic particles within multiple volumes of interest (VOIs) along with structural changes over time using 4D image data. The framework is demonstrated by 4D quantitative analysis of bioactive glass ICIE16 within a 3D-printed scaffold. Here, densification of glass particles within 3 VOIs were tracked and quantified along with diameter change of struts and interstrut pore size over the 3D image series, delivering new insights on the sintering mechanism of ICIE16 bioactive glass particles in both micro and macro scales.

Bioactive glasses incorporating less-common ions to improve biological and physical properties

Bioactive glasses (BGs) have been a focus of research for over five decades for several biomedical applications. Although their use in bone substitution and bone tissue regeneration has gained important attention, recent developments have also seen the expansion of BG applications to the field of soft tissue engineering. Hard and soft tissue repair therapies can benefit from the biological activity of metallic ions released from BGs. These metallic ions are incorporated in the BG network not only for their biological therapeutic effects but also in many cases for influencing the structure and processability of the glass and to impart extra functional properties. The "classical" elements in silicate BG compositions are silicon (Si), phosphorous (P), calcium (Ca), sodium (Na), and potassium (K). In addition, other well-recognized biologically active ions have been incorporated in BGs to provide osteogenic, angiogenic, anti-inflammatory, and antibacterial effects such as zinc (Zn), magnesium (Mg), silver (Ag), strontium (Sr), gallium (Ga), fluorine (F), iron (Fe), cobalt (Co), boron (B), lithium (Li), titanium (Ti), and copper (Cu). More recently, rare earth and other elements considered less common or, some of them, even "exotic" for biomedical applications, have found room as doping elements in BGs to enhance their biological and physical properties. For example, barium (Ba), bismuth (Bi), chlorine (Cl), chromium (Cr), dysprosium (Dy), europium (Eu), gadolinium (Gd), ytterbium (Yb), thulium (Tm), germanium (Ge), gold (Au), holmium (Ho), iodine (I), lanthanum (La), manganese (Mn), molybdenum (Mo), nickel (Ni), niobium (Nb), nitrogen (N), palladium (Pd), rubidium (Rb), samarium (Sm), selenium (Se), tantalum (Ta), tellurium (Te), terbium (Tb), erbium (Er), tin (Sn), tungsten (W), vanadium (V), yttrium (Y) as well as zirconium (Zr) have been included in BGs. These ions have been found to be particularly interesting for enhancing the biological performance of doped BGs in novel compositions for tissue repair (both hard and soft tissue) and for providing, in some cases, extra functionalities to the BG, for example fluorescence, luminescence, radiation shielding, anti-inflammatory, and antibacterial properties. This review summarizes the influence of incorporating such less-common elements in BGs with focus on tissue engineering applications, usually exploiting the bioactivity of the BG in combination with other functional properties imparted by the presence of the added elements.

In Vitro Dissolution of Na-Ca-P-Oxynitrides

Sodium-calcium-phosphate based oxynitride glasses and glass-ceramics doped with Mg, Si, and Nb were studied in vitro in simulated body fluid (SBF) under static conditions. The release of ions and pH changes up to 7 days of immersion were investigated. The nitrogen incorporation into phosphate glass matrix was found to notably influence in vitro dissolution only of homogenous glasses. Increasing the nitrogen content in the samples decreased the mean mass loss, while the niobate incorporation increased it. The correlation between the nitrogen content and increase in pH of SBF was also observed. The presence of phosphates crystallites was found to support the dissolution process at the beginning step (up to 3 days).

Molybdenum trioxide enhances viability, osteogenic differentiation and extracellular matrix formation of human bone marrow-derived mesenchymal stromal cells

BACKGROUND

Metals and their ions allow specific modifications of the biological properties of bioactive materials that are intended for application in bone tissue engineering. While there is some evidence about the impact of particles derived from orthopedic Cobalt-Chromium-Molybdenum (Co-Cr-Mo) alloys on cells, there is only limited data regarding the influence of the essential trace element Mo and its ions on the viability, osteogenic differentiation as well as on the formation and maturation of the primitive extracellular matrix (ECM) of primary human bone marrow-derived stromal cells (BMSCs) available so far.

METHODS

In this study, the influence of a wide range of molybdenum (VI) trioxide (MoO₃), concentrations on BMSC viability was evaluated via measurement of fluorescein diacetate metabolization. Thereafter, the impact of three non-cytotoxic concentrations of MoO₃ on the cellular osteogenic differentiation as well as on ECM formation and maturation of BMSCs was assessed.

RESULTS

MoO₃ had no negative influence on BMSC viability in most tested concentrations, as viability was in fact even enhanced. Only the highest concentration (10 mM) of MoO₃ showed cytotoxic effects. Cellular osteogenic differentiation, measured via the marker enzyme alkaline phosphatase was enhanced by the presence of MoO₃ in a concentration-dependent manner. Furthermore, MoO₃ showed a positive influence on the expression of relevant marker genes for osteogenic differentiation (osteopontin, osteocalcin and type I collagen alpha 1) and on the formation and maturation of the primitive ECM, as measured by collagen deposition and ECM calcification.

CONCLUSION

MoO₃ is considered as an attractive candidate for supplementation in biomaterials and qualifies for further research.

An In Vitro Evaluation of the Biological and Osteogenic Properties of Magnesium-Doped Bioactive Glasses for Application in Bone Tissue Engineering

Magnesium (Mg2+) is known to play a crucial role in mineral and matrix metabolism of bone tissue and is thus increasingly considered in the field of bone tissue engineering. Bioactive glasses (BGs) offer the promising possibility of the incorporation and local delivery of therapeutically active ions as Mg2+. In this study, two Mg2+-doped derivatives of the ICIE16-BG composition (49.46 SiO2, 36.27 CaO, 6.6 Na2O, 1.07 P2O5, 6.6 K2O (mol%)), namely 6Mg-BG (49.46 SiO2, 30.27 CaO, 6.6 Na2O, 1.07 P2O5, 6.6 K2O, 6.0 MgO (mol%) and 3Mg-BG (49.46 SiO2, 33.27 CaO, 6.6 Na2O, 1.07 P2O5, 6.6 K2O, 3.0 MgO (mol%)) were examined. Their influence on viability, proliferation and osteogenic differentiation of human mesenchymal stromal cells (MSCs) was explored in comparison to the original ICIE16-BG. All BGs showed good biocompatibility. The Mg2+-doped BGs had a positive influence on MSC viability alongside with inhibiting effects on MSC proliferation. A strong induction of osteogenic differentiation markers was observed, with the Mg2+-doped BGs significantly outperforming the ICIE16-BG regarding the expression of genes encoding for protein members of the osseous extracellular matrix (ECM) at certain observation time points. However, an overall Mg2+-induced enhancement of the expression of genes encoding for ECM proteins could not be observed, possibly due to a too moderate Mg2+ release. By adaption of the Mg2+ release from BGs, an even stronger impact on the expression of genes encoding for ECM proteins might be achieved. Furthermore, other BG-types such as mesoporous BGs might provide a higher local presence of the therapeutically active ions and should therefore be considered for upcoming studies.

Effect of Simultaneous Sintering of Bioglass to a Zirconia Core on Properties and Bond Strength

This study aimed to assess bioglass sintering to a zirconia core on surface properties and bonding strength to resin cement. Zirconia specimens were divided into four groups: G I: sintered; G II: bioglass modified zirconia (a bioglass slurry was sintered with zirconia at 1550 °C); G III: sandblasted using 50 μm Al₂O₃ particles; and G IV: Z-prime plus application. Surface morphology and chemical analysis were studied using a scanning electron microscope and energy-dispersive spectroscopy. Surface roughness was evaluated using a profilometer. Surface hardness was measured using an indentation tester. For the microshear bond strength test, resin cement cylinders were bonded to a zirconia surface. Half of the specimens were tested after 24 h; the other half were thermocycled (5-55 °C) for 1000 cycles. A shearing load was applied at a crosshead speed of 0.5 mm/min on a universal testing machine. Data were analyzed with ANOVA using SPSS software at (p < 0.05). Results: tThe mean surface roughness of G II was significantly higher than G I and G III. The microhardness of G II was significantly lower than all groups. For bond strength, there was no significant difference between groups II, III, and IV after thermocycling. Conclusions: Bioactive glass can increase the bond strength of zirconia to resin cement, and is comparable to sandblasting and Z-prime bonding agents.

Sol-Gel Synthesis and Characterization of a Quaternary Bioglass for Bone Regeneration and Tissue Engineering

Sol-gel synthesis using inorganic and/or organic precursors that undergo hydrolysis and condensation at room temperature is a very attractive and less energetic method for preparing bioactive glass (BG) compositions, as an alternative to the melt-quenching process. When properly conducted, sol-gel synthesis might result in amorphous structures, with all of the components intimately mixed at the atomic scale. Moreover, developing new and better performing materials for bone tissue engineering is a growing concern, as the aging of the world's population leads to lower bone density and osteoporosis. This work describes the sol-gel synthesis of a novel quaternary silicate-based BG with the composition 60 SiO2-34 CaO-4 MgO-2 P2O5 (mol%), which was prepared using acidified distilled water as a single solvent. By controlling the kinetics of the hydrolysis and condensation steps, an amorphous glass structure could be obtained. The XRD results of samples calcined within the temperature range of 600-900 °C demonstrated that the amorphous nature was maintained until 800 °C, followed by partial crystallization at 900 °C. The specific surface area-an important factor in osteoconduction-was also evaluated over different temperatures, ranging from 160.6 ± 0.8 m2/g at 600 °C to 2.2 ± 0.1 m2/g at 900 °C, accompanied by consistent changes in average pore size and pore size distribution. The immersion of the BG particles in simulated body fluid (SBF) led to the formation of an extensive apatite layer on its surface. These overall results indicate that the proposed material is very promising for biomedical applications in bone regeneration and tissue engineering.

Selective and caspase-independent cytotoxicity of bioactive glasses towards giant cell tumor of bone derived neoplastic stromal cells but not to bone marrow derived stromal cells

Semi-malignant giant cell tumors of bone (GCTB) are associated with large osteolytic defects and significant bone destructions. Surgical resection remains the standard therapy that is, however, associated with very high recurrence rates. Bioactive glasses (BGs) that are osteogenic but under certain conditions also cytotoxic might be suitable to achieve biological reconstruction with simultaneous reduction of tumor recurrence in GCTB. In this study, a concentration and time dependent cytotoxic effect of five different BG compositions towards neoplastic GCTB cells was identified while bone marrow derived mesenchymal stromal cells were mostly unaffected. Time course and extent of the cytotoxic effect were dependent on the BG composition and were not associated with caspases activation, indicating that apoptotic mechanisms are not involved. Rather, detection of BG-induced disruption of the cell membranes and a rapid drop of intracellular HMG1 (High Mobility Group Box 1 protein) levels suggest a necrotic cell death. Notably, the cytotoxic effects were dependent on a direct contact of cells and BGs and could not be observed using indirect cultivation settings. Our data suggest that BGs might represent promising materials for the treatment of GCTB in order to reduce tumor recurrence with simultaneous enhancement of bone regeneration.

Impact of Zinc- or Copper-Doped Mesoporous Bioactive Glass Nanoparticles on the Osteogenic Differentiation and Matrix Formation of Mesenchymal Stromal Cells

Mesoporous bioactive glass nanoparticles (MBGNs) have gained relevance in bone tissue engineering, especially since they can be used as vectors for therapeutically active ions like zinc (Zn) or copper (Cu). In this study, the osteogenic properties of the ionic dissolution products (IDPs) of undoped MBGNs (composition in mol%: 70 SiO₂, 30 CaO) and MBGNs doped with 5 mol% of either Zn (5Zn-MBGNs) or Cu (5Cu-MBGNs; compositions in mol%: 70 SiO₂, 25 CaO, 5 ZnO/CuO) on human bone marrow-derived mesenchymal stromal cells were evaluated. Extracellular matrix (ECM) formation and calcification were assessed, as well as the IDPs’ influence on viability, cellular osteogenic differentiation and the expression of genes encoding for relevant members of the ECM. The IDPs of undoped MBGNs and 5Zn-MBGNs had a comparable influence on cell viability, while it was enhanced by IDPs of 5Cu-MBGNs compared to the other MBGNs. IDPs of 5Cu-MBGNs had slightly positive effects on ECM formation and calcification. 5Zn-MBGNs provided the most favorable pro-osteogenic properties since they increased not only cellular osteogenic differentiation and ECM-related gene expression but also ECM formation and calcification significantly. Future studies should analyze other relevant properties of MBGNs, such as their impact on angiogenesis.

A novel hydrogel scaffold contained bioactive glass nanowhisker (BGnW) for osteogenic differentiation of human mesenchymal stem cells (hMSCs) in vitro

Employing hydrogels as an alternative strategy for repairing bone defects has received great attention in bone tissue engineering. In this study, hydrogel scaffold based on collagen, gelatin, and glutaraldehyde was combined with bioactive glass nanowhiskers (BGnW) to differentiate human mesenchymal stem cells (hMSCs) into the osteogenic lineage and inducing biomineralization. Pure Gel-Glu-Col and bioactive glass nanowhiskers were used as control throughout the paper. Chemical, physical and morphological characteristics of the nanocomposite scaffold were assessed meticulously using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), porosity measurement, water uptake ability, tensile test, and scanning electron microscopy (SEM). To determine the cytotoxicity and cell viability of the hydrogel, MTT assay and Acridine orange (AO) staining were performed. hMSCs seeded on Gel-Glu-Col/BGnW were then incubated with osteogenic differentiation media for 14 days. Biomineralization assays (alkaline phosphatase (ALP) activity, calcium content assay, von Kossa, and Alizarin red staining) were carried out, and osteogenic genes and protein markers were examined using real time-PCR and immunocytochemistry. Results showed that the components of the hydrogel were properly integrated. The mechanical property of hydrogel was enhanced following the addition of BGnW. Cell viability assays confirmed the biocompatibility of the scaffold and increasing the proliferation after incorporating BGnW into pure Ge1-Glu-Col. Our nanocomposite maintained an enhanced ability of biomineralization as compared to its pure counterparts. Molecular investigations revealed an elevated level of osteogenic markers as compared to Ge1-Glu-Col and BGnW. All in all, Gel-Glu-Col/BGnW seems to be a potential candidate for the regeneration of bone tissue.

Effect of manganese, zinc, and copper on the biological and osteogenic properties of mesoporous bioactive glass nanoparticles

Mesoporous bioactive glass nanoparticles (MBGNs) have demonstrated promising properties for the local delivery of therapeutically active ions with the aim to improve their osteogenic properties. Manganese (Mn), zinc (Zn), and copper (Cu) ions have already shown promising pro-osteogenic properties. Therefore, the concentration-dependent impact of MBGNs (composition in mol%: 70 SiO₂ , 30 CaO) and MBGNs containing 5 mol% of either Mn, Zn, or Cu (composition in mol%: 70 SiO₂ , 25 CaO, 5 MnO/ZnO/CuO) on the viability and osteogenic differentiation of human marrow-derived mesenchymal stromal cells (BMSCs) was assessed in this study. Mn-doped MBGNs (5Mn-MBGNs) showed a small "therapeutic window" with a dose-dependent negative impact on cell viability but increasing pro-osteogenic features alongside increasing Mn concentrations. Due to a constant release of Zn, 5Zn-MBGNs showed good cytocompatibility and upregulated the expression of genes encoding for relevant members of the osseous extracellular matrix during the later stages of cultivation. In contrast to all other groups, BMSC viability increased with increasing concentration of Cu-doped MBGNs (5Cu-MBGNs). Furthermore, 5Cu-MBGNs induced an increase in alkaline phosphatase activity. In conclusion, doping with Mn, Zn, or Cu can enhance the biological properties of MBGNs in different ways for their potential use in bone regeneration approaches.

Synergistic effect of adding bioglass and carbon nanotubes on poly (lactic acid) porous membranes for guided bone regeneration

Polymer membranes have been widely used in guided bone regeneration (GBR), especially when it comes to their use in dentistry. Poly (lactic acid) (PLA) have good mechanical properties such as flexibility, which allows the material to be moldable and also has biocompatibility and biodegradation. Besides that, bioglass (BG) incorporated into the polymer matrix can promote osteoinduction properties and osteoconduction properties to the polymer-ceramic biocomposite. The membranes are also required to exhibit antimicrobial activity to prevent or control the proliferation of pathogenic microorganisms, and the addition of carbon nanotubes (CNT) can assist in this property. The porous membranes of PLA with the addition of different contents of BG and CNT were obtained by solvent casting in controlled humidity method, and the synergistic effect of the addition of both fillers were investigated. The membranes showed pores (3-11 μm) on their surface. The addition of 5 wt% BG causes an increase in the surface porosity and bioactivity properties of the PLA. The agar diffusion test showed antimicrobial activity in the membranes with addition of CNT. In vitro results showed that the porous membranes were not cytotoxic and allowed cell activity and differentiation. Thus, BG collaborated to increase biological activity while CNT contributed to microbial activity, creating a synergistic effect on PLA porous membranes, being this effect more evident for PLA/5BG/1.0CNT. These results indicated a promising use of this new biomaterial for the production of porous membranes for GBR.

Fabrication and characterization of ZrO2 incorporated SiO2-CaO-P2O5 bioactive glass scaffolds

Sol-gel chemistry offers a flexible, widely accepted methodology that enables the creation of a new generation of bioactive glass (BG). In the current study, a sol-gel method was used to synthesize ZrO₂ incorporated 56SiO₂-34CaO-10P₂O₅ mol% bioactive glass. The highly crystalline structure was composed of small zirconium oxide nanoparticles (ZrO₂) of less than 200 nm in size. It was successfully fabricated using a hydrothermal method. Polyurethane foam (PU) was selected to fabricate a highly porous BG-ZrO₂ scaffold using a foam replica technique. The physicochemical, morphological properties of the BG-ZrO₂ compositions were evaluated using X-ray diffraction (XRD), Fourier transforms infrared (FTIR), thermo-gravimetric analysis (TGA), transmission electron microscope (TEM) and scanning electron microscope (SEM) with energy dispersive spectroscopy (EDS). In-vitro degradation analysis of the BG-ZrO₂ scaffolds was performed after immersion of the samples in simulated body fluid (SBF). The incorporation of ZrO₂ nanoparticles into the bioactive glass matrix enhances both the mechanical strength and thermal stability. Since the novel formed BG-ZrO₂ scaffolds possesses respectable antibacterial properties against some bacterial strains, this renders it an ideal tissue engineering substitute, capable of reducing failure rates in implants.

Preconditioning of Bioactive Glasses before Introduction to Static Cell Culture: What Is Really Necessary?

Due to their high bioreactivity, the in-vitro analysis of bioactive glasses (BGs) can be challenging when it comes to maintaining a physiological pH. To improve BG biocompatibility, a heterogenic spectrum of preconditioning approaches, such as "passivation" of the BGs by incubation in cell culture medium, are used but have never been directly compared. In this study, the effect of passivation periods of up to 72 h on pH alkalization and viability of human bone marrow-derived mesenchymal stromal cells was evaluated to determine a time-efficient passivation protocol using granules based on the 45S5-BG composition (in wt%: 45.0 SiO2, 24.5 Na2O, 24.5 CaO, 6.0 P2O5) in different concentrations. pH alkalization was most reduced after passivation of 24 h. Cell viability continuously improved with increasing passivation time being significantly higher after passivation of at least 24 h compared to non-passivated 45S5-BG and the necessary passivation time increased with increasing BG concentrations. In this setting, a passivation period of 24 h presented as an effective approach to provide a biocompatible cell culture setting. In conclusion, before introduction of BGs in cell culture, different passivation periods should be evaluated in order to meet the respective experimental settings, e.g., by following the experimental protocols used in this study.

Combined Fluorescence-Based in Vitro Assay for the Simultaneous Detection of Cell Viability and Alkaline Phosphatase Activity during Osteogenic Differentiation of Osteoblast Precursor Cells

Novel bone substitute materials need to be evaluated in terms of their osteogenic differentiation capacity and possible unwanted cytotoxic effects in order to identify promising candidates for the therapy of bone defects. The activity of alkaline phosphatase (ALP) is frequently quantified as an osteogenic marker, while various colorimetric assays, like MTT assay, are used to monitor cell viability. In addition, the DNA or protein content of the samples needs to be quantified for normalization purposes. As this approach is time consuming and often requires the analysis of multiple samples, we aimed to simplify this process and established a protocol for the combined fluorescence-based quantification of ALP activity and cell viability within one single measurement. We demonstrate that the fluorogenic substrate 4-methylumbelliferone-phosphate (4-MUP) and the commonly used para-nitrophenylphosphate (p-NPP) produce comparable and highly correlating results. We further show that fluorescein–diacetate (FDA) can be used to quantify both cell viability and cell number without interfering with the quantification of ALP activity. The measurement of additional normalization parameters is, therefore, unnecessary. Therefore, the presented assay allows for a time-efficient, simple and reliable analysis of both ALP activity and cell viability from one sample and might facilitate experiments evaluating the osteogenic differentiation of osteoblast precursor cells.