[M-IS12] Interface- and nano-phenomena on crystal growth and dissolution

[MIS12-09] Intercalated Molecule Exchange Process of Thiomalate Substituted Octacalcium Phosphate Crystals during Phase Conversion

*Yuki Sugiura¹, Masanori Horie¹ (1.National Institute of Advanced Industrial Science and Technology)

Keywords:Calcium phosphate, Ion exchange, phase conversion

Octacalcium phosphate (OCP) is a layered calcium phosphate compound that has attracted significant attention as a new biomaterial due to its excellent biocompatibility. Its interlayer structure, known as HPO₄-OH layer, can be easily replaced by dicarboxylic acid. However, the ionic and/or molecular exchange process of substituted dicarboxylic acid into OCP interlayer is still unclear. Therefore, in this study, we evaluate the molecular exchange process for thiomalate (SH-malate)-substituted OCP (OCP-SH-malate) during the phase conversion process to other phases in disodium hydrogen phosphate solution (Na₂HPO₄). When the OCP-SH-malate is immersed in 1 mol/L Na₂HPO₄ at 40 °C while shaking at 200 rpm, SH-malate, first desorbed from the interlayer of OCP-SH-malate and the HPO₄-OH layer structure, is formed at the interlayer where the SH-malate was dissolved. The HPO₄-OH layer structure is unstable, making it easily convert to hydroxyapatite (HAp) via dehydration upon further immersion. During this reaction, besides the dissolution of marginal edges of the crystals, crystals morphology was no obvious changes, neither were there evidences of dissolution and collapsing of OCP crystals nor nucleation of newly created crystals.