Controllable synthesis of poly(acrylic acid)-stabilized nano-hydroxyapatite suspension by an ultrasound-assisted precipitation method

An improved precipitation method was developed to prepare stable nano-hydroxyapatite (HAP) suspension with the aid of steric effect of poly(acrylic acid) (PAA) and acoustic cavitation effect. The effects of reaction temperature and PAA concentration on the formation of nano-HAP suspension were studied. The rising temperature led to the transformation of spherical amorphous calcium phosphate (ACP) to needle-like nano-HAP crystals with the increase in size. The increasing PAA concentration mightily hindered the crystallization of HAP instead of decreasing the size. PAA provided steric effect to stabilize nano-HAP in solution due to the electrostatic interaction between -COO- of PAA and Ca2+ on the surface of HAP. The obtained PAA-stabilized nano-HAP suspension showed good stability in different media (water, PBS, RPMI 1640) and noncytotoxicity. This study provides a potential technology for the controllable synthesis of stable nano-HAP suspension.