Formation of uniform hydroxyapatite nanocoating triggered by nucleation at carboxylic groups embedded in ethylene/acrylic acid copolymer microspheres

A uniform thin layer of hydroxyapatite (HAp) was formed by promoting its nucleation at carboxylic groups on the surface of the substrate. In the present work, we chose ethylene (82 wt%)/acrylic acid (18 wt%) copolymer microsphere as the substrate. The HAp moiety was directly derived from calcium hydrogenphosphate with excess calcium ion in an aqueous phase at a basic condition adjusted with ammonia aqueous solution (pH ∼ 11). The TEM observation revealed that a dense coating layer with the thickness below 100 nm was formed on the surface of the copolymer microsphere. The coating layer was formed from rod-like HAp nanoparticles, which were densely stacked with each other. The carboxylic groups of the copolymerised acrylic acid promoted the nucleation and formation of the primary precursory layer of HAp on the surface of the copolymer microsphere.