Osteoclast formation in the co-presence of octacalcium phosphate and inorganic phosphorus-containing gelatin <i>in vitro</i>

This study was designed to investigate the effect of biodegradable octacalcium phosphate (OCP) bone substitute on osteoclast formation under the higher inorganic phosphorus concentration in vitro. We developed the gelatin particles releasing inorganic phosphate (Pi) ions as a model to change the local Pi ion concentration around OCP in the OCP/gelatin composite materials. Spectroscopic and chemical analyses indicated that Pi ion released around 2 mmol/L from gelatin particles promoted OCP hydrolysis, although excessive Pi ion release up to around 3 mmol/L suppressed the hydrolysis. The formation of tartrate-resistant acid phosphatase (TRAP)-positive multinuclear cells was increased by the OCP hydrolysis promotion via modulately higher Pi release Pi ion release. However, OCP hydrolysis suppression by excessive Pi ion release decreased the formation of TRAP-positive cells. The present study suggests that the chemical environment induced by OCP hydrolysis under a suitable Pi ion concentration could be associated with promoting osteoclast formation.