Surface Modification of Hydroxyapatite Nanoparticles with Thermal‐Responsive PNIPAM by ATRP

Hydroxyapatite (HA) nanoparticles grafted by poly( N ‐isopropylacrylamide) (PNIPAM) brushes (PNIPAM‐ g ‐HA) have been synthesized by the surface‐initiated atom transfer radical polymerization (ATRP) of N ‐isopropylacrylamide (NIPAM). The surface grafting amount of PNIPAM ranges from 15.5% to 46.4%. PNIPAM‐ g ‐HA has been characterized by FT‐IR spectroscopy, thermal gravimetric analysis, X‐ray diffraction, and scanning electron microscopy (SEM). The UV transmittance spectra and the particle size analysis of PNIPAM‐ g ‐HA in aqueous solution demonstrates that the PNIPAM‐ g ‐HA possess reversible thermal stimuli responsive properties. An in vitro bioactivity assessment indicates that PNIPAM‐ g ‐HA can induce the mineralization of Ca 2+ and HPO   4 2−and possesses an excellent bioactivity. The cell culture results show that the cells adhered to the surface of PNIPAM‐ g ‐HA grow better than on HA, and the area of the cells on the surface of PNIPAM‐g‐HA is much greater than for HA, which proves that the PNIPAM‐ g ‐HA has a better biocompatibility than HA.