Bioactive glass-ceramic for bone tissue engineering: an in vitro and in vivo study focusing on osteoclasts

Biological effects of a zinc-substituted borosilicate bioactive glass on human bone marrow derived stromal cells in vitro and in a critical-size femoral defect model in rats in vivo

The borosilicate 0106-B1-bioactive glass (BG) composition (in wt%: 37.5 SiO2, 22.6 CaO, 5.9 Na2O, 4.0P2O5, 12.0 K2O, 5.5 MgO, 12.5 B2O3) has shown favorable processing characteristics and bone regeneration ability. This study investigated the addition of zinc (Zn) to 0106-B1-BG as an approach to improve this BG's biological properties. Different proportions of ZnO were substituted for CaO in 0106-B1-BG, resulting in three new BG-compositions: 1-Zn-BG, 2-Zn-BG, 3-Zn-BG (in wt%: 37.5 SiO2, 21.6/20.1/17.6 CaO, 4.0 P2O5, 5.9 Na2O, 12.0 K2O, 5.5 MgO, 12.5 B2O3 and 1.0/2.5/5.0 ZnO). Effects of the BG compositions on cytocompatibility, osteogenic differentiation, extracellular matrix deposition, and angiogenic response of human bone marrow-derived mesenchymal stromal cells (BMSCs) were evaluated in vitro. Angiogenic effects were assessed using a tube formation assay containing human umbilical vein endothelial cells. The in vivo osteogenic and angiogenic potentials of 3-Zn-BG were investigated in comparison to the Zn-free 0106-B1-BG in a rodent critical-size femoral defect model. The osteogenic differentiation of BMSCs improved in the presence of Zn. 3-Zn-BG showed enhanced angiogenic potential, as confirmed by the tube formation assay. While Zn-doped BGs showed clearly superior biological properties in vitro, 3-Zn-BG and 0106-B1-BG equally promoted the formation of new bone in vivo; however, 3-Zn-BG reduced osteoclastic cells and vascular structures in vivo. The acquired data suggests that the differences regarding the in vivo and in vitro results may be due to modulation of inflammatory responses by Zn, as described in the literature. The inflammatory effect should be investigated further to promote clinical applications of Zn-doped BGs.

Zinc- and Fluoride-Releasing Bioactive Glass as a Novel Bone Substitute

Bioglass 45S5, a silica-based glass, has pioneered a new field of biomaterials. Bioglass 45S5 promotes mineralization through calcium ion release and is widely used in the dental field, including toothpaste formulations. However, the use of Bioglass 45S5 for bone grafting is limited owing to the induction of inflammation, as well as reduced degradation and ion release. Phosphate-based glasses exhibit higher solubility and ion release than silica-based glass. Given that these glasses can be synthesized at low temperatures (approximately 1,000°C), they can easily be doped with various metal oxides to confer therapeutic properties. Herein, we fabricated zinc- and fluoride-doped phosphate-based glass (multicomponent phosphate [MP] bioactive glass) and further doped aluminum oxide into the MP glass (4% Al-MP glass) to overcome the striking solubility of phosphate-based glass. Increased amounts of zinc and fluoride ions were detected in water containing the MP glass. Doping of aluminum oxide into the MP glass suppressed the striking dissolution in water, with 4% Al-MP glass exhibiting the highest stability in water. Compared with Bioglass 45S5, 4% Al-MP glass in water had a notably reduced particle size, supporting the abundant ion release of 4% Al-MP glass. Compared with Bioglass 45S5, 4% Al-MP glass enhanced the osteogenesis of mouse bone marrow-derived mesenchymal stem cells. Mouse macrophages cultured with 4% Al-MP glass displayed enhanced induction of anti-inflammatory M2 macrophages and reduced proinflammatory M1 macrophages, indicating M2 polarization. Upon implanting 4% Al-MP glass or Bioglass 45S5 in a mouse calvarial defect, 4% Al-MP glass promoted significant bone regeneration when compared with Bioglass 45S5. Hence, we successfully fabricated zinc- and fluoride-releasing bioactive glasses with improved osteogenic and anti-inflammatory properties, which could serve as a promising biomaterial for bone regeneration.

Anti-resorption role of low-intensity pulsed ultrasound (LIPUS) during large-scale bone reconstruction using porous titanium alloy scaffolds through inhibiting osteoclast differentiation

BACKGROUND

Ti6Al4V biomaterials combine with low-intensity pulsed ultrasound (LIPUS) has been reported with great bone regeneration capacity. It is important to better understand how LIPUS benefits bone microenvironment to seek for target of therapeutic medicine. Osteoclast differentiation plays a crucial role in bone resorption. Recent advances in molecular biology have revealed that N6-methyladenosine (m6A) RNA modifications can modulate biological processes, but their role in bone biology, particularly in osteoclast differentiation, remains unclear. We aim to understand how LIPUS regulates bone microenvironment especially osteoclast formation during bone regeneration to provide new therapeutic options for preventing and delaying bone resorption, thus with better bone regeneration efficiency.

RESULTS

1. LIPUS promoted bone ingrowth and bone maturity while inhibiting osteoclast formation within Ti6Al4V scaffolds in large-scale bone defect model. 2. LIPUS was found to inhibit osteoclast differentiation by decreasing the overall expression of osteoclast markers in vitro. 3. LIPUS decreases RNA m6A-modification level through upregulating FTO expression during osteoclast differentiation during. 4. Inhibiting FTO expression and function leads to less inhibition during osteoclast differentiation.

CONCLUSION

LIPUS suppresses osteoclast differentiation during bone regeneration through reducing m6A modification of osteoclastic RNAs by up regulating FTO expression.

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.