Human osteoblasts grow transitional Si/N apatite in quickly osteointegrated Si3N4 cervical insert.

Silicon nitride (Si3N4) ceramics possesses surface chemistry that accelerates bone repair, as previously established by in vitro experiments using both osteosarcoma and mesenchymal cells. The release of silicic acid and nitrogen compounds from the surface Si3N4 enhanced in vitro cellular activity. The results of this study demonstrate for the first time that the osseointegration behavior previously observed is operative with a peculiar chemistry within the human milieu. Si and N elements stimulated progenitor cell differentiation and osteoblastic activity, which ultimately resulted in accelerated bone ingrowth. At the molecular scale, insight into the effect of silicon and nitrogen ions released from the Si3N4 surface was obtained through combined histomorphometric analyses, Raman, Fourier-transform-infrared, and X-ray photoelectron spectroscopies. Identical analyses conducted on a polyetheretherketone (PEEK) spinal explant showed no chemical changes and a lower propensity for osteogenic activity. Silicon and nitrogen are key elements in stimulating cells to generate bony apatite with crystallographic imperfections, leading to enhanced bioactivity of Si3N4 biomedical devices. STATEMENT OF SIGNIFICANCE: This research studies osseointegration processes comparing results from explanted PEEK and Si3N4 spinal spacers. Data show that the formation of hydroxyapatite on silicon nitride bio-ceramic surfaces happens with a peculiar mechanism inside the human body. Silicon and nitrogen were incorporated inside the bony tissue structure allowing the developing of off-stoichiometric bony apatite and stimulating progenitor cell differentiation/osteoblastic activity. Silicon and nitrogen ions released from the Si3N4 surface were detected through combined histologic analyses, Raman microspectroscopy, Fourier-transform-infrared, and X-ray photoelectron spectroscopies.