Silicon Nitride Induces Osteoconduction Via Activated Mitochondrial Oxidative Phosphorylation and Neovascularization

Abstract

Silicon nitride (Si3N4: SiN) is a thermodynamically stable ceramic material with excellent mechanical properties, and wear and corrosion resistance for industrial applications. SiN has been proposed for orthopedic and dental implant applications owing to its enhanced osteoconduction. However, the biological mechanisms underlying SiN-induced bone formation have not been fully elucidated. In this study, SiN significantly increased in vitro mineralization of human bone marrow mesenchymal stromal cells (BM-MSC) and in vivo peri-implant bone volume in mouse femurs compared to conventionally used titanium (Ti) implants. RNA sequencing of BM-MSC cultured on SiN disks revealed that functional gene clusters associated with mitochondrial oxidative phosphorylation were significantly elevated. SiN in an aqueous solution has been shown to release ammonium/ammonia, which may provide a source for glutamine-dependent energy production, and BM-MSC upregulated the expression of a key enzyme, glutamate-ammonia ligase under osteogenic conditions. Additionally, SiN increased the expression of functional gene clusters involved in vascular formation. The upregulation of HIF1a in vitro and increased VEGFR3-positive blanching vascular structures in vivo implied that SiN induced neovascularization. This study revealed an important mechanism through which SiN stimulated osteoconduction by unique glutamine-driven mitochondrial oxidative phosphorylation and established oxygen and nutrient supply by neovascularization, leading to stable osseointegration.