Material Science & Engineering World Conference 2026

Abstract

Hydroxyapatite (HA) is a bioactive ceramic commonly used in bone implant applications due to its ability to form an apatite layer under physiological conditions. In this study, the effects of immersion temperature (32 °C and 37 °C) and simulated body fluid (SBF) composition (Tas-type and Kokubo-type) on calcium ion concentration, reaction kinetics, and mass change of HA were investigated through an 18-day in vitro immersion test. Calcium ion concentration was measured using complexometric titration, and kinetic analysis was performed using the integral method. The results showed an initial increase in calcium ion concentration due to ion release from the HA surface, followed by a gradual decrease associated with apatite precipitation. The calcium depletion process followed first-order reaction kinetics under all conditions. A higher reaction rate constant was obtained at 37°C compared to 32°C, indicating enhanced ion diffusion and precipitation kinetics at physiological temperature. Furthermore, Tas-type SBF, which contains a bicarbonate ion concentration closer to that of human blood plasma, exhibited better kinetic linearity, lower model error, and more pronounced mass gain than Kokubo-type SBF. These findings demonstrate that both immersion temperature and SBF composition significantly influence the bioactivity of hydroxyapatite, and the use of physiologically relevant conditions is essential for reliable in vitro bioactivity evaluation.