Low-Temperature Synthesis and Surface Modification of High Surface Area Calcium Hydroxyapatite Nanorods Incorporating Organofunctionalized Surfaces

A new low-temperature continuous approach for the surface modification of hydroxyapatite (HA) is described. In this method, the HA particle surfaces were modified using methacrylic acid, vinylphosphonic acid, adipic acid, citric acid, or polyvinyalcohol, respectively, using a continuous plastic flow synthesis (CPFS) system at a reaction temperature of 70 °C for 5 min. The materials were investigated using a range of analytical techniques, including TEM (transmission electron microscopy), zeta potential, XRD (X-ray diffraction), BET (Brunauer–Emmett–Teller) surface area analysis, FTIR (Fourier transform infrared) spectroscopy, and XPS (X-ray photoelectron spectroscopy). The presence of organic agents in the reagents, resulted in a significant reduction in particle size of the nano-HA rods; TEM studies confirmed the formation of highly dispersed nanorods of HA with average lengths and diameters in the ranges 20–60 nm and 4–10 nm, respectively. XPS analyses suggested that the Ca:P molar ratio decreased from 1.67 to ca. 1.34 by the addition of organic surface agents. The zeta potential measurements revealed that the colloidal stability of surface-modified HA generally increased (under certain conditions) compared to ungrafted HA. The small size and presence of functional groups make these materials potentially suitable for dental restoration fillers and composite bone regeneration applications.