Fluorescence microscopic analysis of bone osseointegration of strontium-substituted hydroxyapatite implants

The purpose of this study was to analyze the effect of strontium-substituted hydroxyapatite (Sr-HA) on bone osseointegration of the implants using fluorescence microscopy. We allocated 20 implants to two groups: Sr-HA group and HA group. Electrochemically deposited HA and Sr-HA coatings were applied onto the implants separately. All the implants were inserted into femur bone of rabbits. Oxytetracycline hydrochloride, alizarin-complexon, and calcein green were respectively administered 7, 28, and 46 d after the implantation. After eight weeks, femurs were retrieved and prepared for the fluorescence microscopy observation. We analyzed the bone mineral apposition rates (MARs), bone area ratios (BARs), and bone to implant contact (BIC) of the two groups. Fluorescence microscopic observation showed that all groups exhibited extensive early peri-implant bone formation. The MAR of the Sr-HA group was greater than that for pure HA from 7 to 28 d after implantation, but no significant difference was found at later stage. And the BIC showed difference at 7 and 28 d compared with pure HA. We concluded that Sr-HA coating can improve the bone osseointegration of the implant in the early stage compared with the HA coating.

Strontium-substituted sub-micron bioactive glasses inhibit ostoclastogenesis through suppression of RANKL-induced signaling pathway

Strontium-substituted bioactive glass(Sr-BG)has shown superior performance in bone regeneration.Sr-BG-induced osteogenesis has been extensively studied;however,Sr-BG-mediated osteoclastogenesis and the underlying molecular mechanism remain unclear.It is recognized that the balance of osteogenesis and osteoclastogenesis is closely related to bone repair,and the receptor activators of nuclear factor kappaB ligand(RANKL)signaling pathway plays a key role of in the regulation of osteoclastogenesis.Herein,we studied the potential impact and underling mechanism of strontium-substituted sub-micron bioactive glass(Sr-SBG)on RANKL-induced osteoclast activation and differentiation in vitro.As expected,Sr-SBG inhibited RANKL-mediated osteoclastogenesis significantly with the experimental performance of decreased mature osteoclasts formation and downregulation of osteoclastogenesis-related gene expression.Furthermore,it was found that Sr-SBG might suppress osteoclastogenesis by the combined effect of strontium and silicon released through inhibition of RANKL-induced activation of p38 and NF-κB pathway.These results elaborated the effect of Sr-SBG-based materials on osteoclastogenesis through RANKLinduced downstream pathway and might represent a significant guidance for designing better bone repair materials.