Biomimetic deposition of hydroxyapatite on brushite single crystals grown by the gel technique

Abstract

Recently, attention has been paid to the production of hydroxyapatite (HA) single crystals or whiskers for making a variety of bioactive composites as new implant materials. Brushite single crystals were grown by gel technique at room temperature by chemical reaction method using Ca(NO3)2 · 4H2O and (NH4)2HPO4 as the reactants. Sodium silicate solution was used as the gel medium. The growth parameters, such as the gel density, concentration of the two reactants and pH of the medium, were varied to optimize the suitable growth conditions of brushite crystals. Single crystals of brushite of size nearly 10 mm in length were obtained when 1 M of (NH4)2HPO4 and 2 M of Ca(NO3)2 · 4H2O were used as the inner and outer reactants, respectively. The grown crystals were used as the seed crystals for HA deposition under electrochemical hydrothermal treatment in SBF solution. Experiments were performed by varying the temperature from 80°C to 200°C, current from 25 to 150 mA, and time from 10 to 60 min. A thick layer deposition of HA was obtained at 140°C for a time interval of 30 min by passing 100-mA current. Brushite single crystals and HA-coated brushite crystals were subjected to various characterizations, such as XRD, FTIR and SEM, to confirm the HA deposition on brushite. © 2001 Elsevier Science B.V.