Site-Selective Adhesion of Hydroxyapatite Microparticles on Charged Surfaces in a Supersaturated Solution

Abstract

Site-selective adhesion of hydroxyapatite (HAp) microparticles to NH2-terminated self-assembled monolayers (NH2–SAM, positive surface) and OH–SAM (negative) was investigated in the present paper. HAp microparticles were measured to be negatively charged, and homogeneously formed at 50°C in the simulated body fluid (SBF) with high supersaturation degree (1.5 SBF; the concentrations of Ca2+ and PO43− alone are 1.5 times that in 1.0 SBF) buffered carefully at 7.6∼7.7. The zeta potential of microparticles decreased from −11.5 mV to neutrality owing to the absorption of cations accompanied by the simultaneous growth of microparticles. The micropattern of HAp particulate films was successfully fabricated by the use of site-selective adhesion of HAp microparticles on the positive NH2–SAM owing to the attractive electrostatic interactions. The quantitative analysis using quartz crystal microbalance also confirmed the identical phenomena.