Biomimetic apatite formation on poly(lactic acid) composites containing calcium carbonates

Poly(lactic acid) composites containing a mixture of calcium carbonates (vaterite, aragonite, and calcite) were prepared by a carbonation process in methanol. Soaking of the composites for 3 h in simulated body fluid (SBF) at 37 °C resulted in the deposition of bonelike apatite particles on the composite surface. After soaking the composites, vaterite phase in the composites was forward to dissolve rapidly, resulting in increase the supersaturation of the apatite in SBF. ¹³C cross-polarization magic angle spinning nuclear magnetic resonance (¹³C CP/MAS-NMR) spectra of the composites suggested the formation of a bond between Ca²⁺ ion and the COO^- group, which induces the apatite nucleation. These results may elucidate the mechanism of means to reduce the induction period for apatite formation.