Surface modification of nano-apatite by grafting organic polymer

Since surface properties of hydroxyapatite (HA) play an important role in its performance, surface modification of HA has gained much attention from researchers. Silane coupling agents have been the focus of the research. In this study, an effective surface modification method was developed using hexamethylene diisocyanate as a coupling agent. Polyethylene glycol (Mw=1500) was successfully coupled to the surface of nano-size apatite particles (nano-apatite). Various methods were used to characterize the surface-modified nano-apatite. Infra-red spectra confirmed the existence of a layer of polymer with both urethane and ether linkage on the surface of nano-apatite. The amount of grafted polymer as determined by total organic carbon analysis (TOC) and thermal gravimetric analysis (TGA) was about 20% in weight. Solid 1H MAS NMR spectra indicated that the amount of hydroxyl groups of nano-apatite was decreased by 7.7% after surface grafting reaction. It is concluded that the surface hydroxyl groups of nano-apatite have the reactivity towards isocyanate groups.