Synthesis of poly(ethylene glycol)-functionalized hydroxyapatite organic colloid intended for nanocomposites

Traditional modifications to hydroxyapatite (HA) nanoparticles usually occurred after HA synthesis and thus are insufficient to avoid particle agglomeration. In this study, a new heterofunctional poly(ethylene glycol) (PEG) with phosphoric acid and carboxyl end groups, i.e., α-(N-2-phosphoethyl phosphoric acid)-amide, ω-carboxyl-bismethyoxy poly(ethylene glycol) (ADP-PEG-COOH), was synthesized as an in situ surface modifier to HA nanoparticles. The resulting modified HA (ADP-PEG-HA) can disperse in methanol, forming a colloid stabilized by peripheral carboxyl-endcapped PEG chains. The colloidal particles resembled nanospheres which agglomerated to some extent under examination by transmission electron microscope. This highly dispersible HA nanoparticles in organic solvent might find application in preparing new HA nanocomposites.