(502e) Biomimetic Self-Assembling Copolymer–Hydroxyapatite Nanocomposites with the Nanocrystal Size Controlled by Citrate

Bone is a nanocomposite that mainly contains nano-sized hydroxyapatite (HAp) crystals and the fibrous protein collagen. Citrate binds strongly to the surface of HAp nanocrystals in bone and is thought to prevent crystal thickening. In this work, biomimetic self-assembled copolymer-HAp nanocomposites were synthesized using a bottom-up approach from aqueous solutions. Amphiphilic block copolymer Pluronic F127 was used as a template for the growth of HAp nanocrystals.  Citrate was added as a biomimetic regulatory element to control of the size and stability of HAp nanocrystals in synthetic nanocomposites. The decrease of the HAp crystal size within the polymer matrix with increasing citrate concentration was confirmed by solid-state nuclear magnetic resonance (NMR) techniques and wide-angle X-ray diffraction (XRD). The shapes of HAp nanocrystals were determined by transmission electron microscopy (TEM). Small angle neutron scattering (SANS) results indicated that the nanocrystals are incorporated into the polymer matrix in a manner that does not disrupt the self-assembled structure of the pluronic micelles. The surface-to-volume ratios determined by advanced NMR spectroscopy show that 0, 2, 10, and 40 mM citrate changed the thicknesses of the HAp crystals from 4 nm without citrate to 2.9, 2.8, and 2.3 nm, respectively. With citrate concentrations comparable to that in body fluids, HAp nanocrystals of similar sizes and morphologies as in avian and bovine bones have been fabricated in vitro.