“Reservoir” and “barrier” effects of ABC block copolymer micelle in hydroxyapatite mineralization control

An amphiphilic triblock poly (ethylene glycol)-block-poly (acrylate acid)-block-poly (ε-caprolactone) (PEG-PAA-PCL) copolymer was synthesized by sequential anionic polymerization. By comparing with diblock copolymer poly (acrylic acid)-block-poly (ε-caprolactone) (PAA-PCL), the triblock copolymer (PEG-PAA-PCL) micelle has core-shell-corona structure, which possesses better dispersion, could be a good candidate as structure template for the controlled mineralization of hydroxyapatite (HA). The interactions between inorganic ions and polymers were studied by using Ca2+ ion selective electrode and zeta potential, which indicated the “reservoir” effect of micelles and the “barrier” effect of PEG segments during mineralization process. Ca2+ ions can penetrate through the corona and interact with PAA segments. When PO43− ions were added, Ca2+ ions diffuse out, and react with PO43− ions to form the new apatite layer. Thus the supersaturation could be well tuned by the triblock copolymer micelles, and the nucleation and crystal growth in nano scale could be controlled by appropriate usage of this template system.