Evaluation of electrical polarizability and in vitro bioactivity of apatite Sr5(PO4)3OH dense ceramics

Abstract

Dense ceramics of Sr5(PO4)3OH (strontium hydroxide tris-phosphate with an apatite structure; Sr-HAp) with little dehydration were successfully synthesized in a humid atmosphere. Polarization of these Sr-HAp ceramics was performed by application of an external dc field at higher temperature. To clarify the polarization and depolarization phenomena of Sr-HAp, the polarized samples were analyzed by thermally stimulated depolarization current (TSDC) measurement. The features of the TSDC spectra were very similar to those of the isomorphic hydroxyapatite (Ca5(PO4)3OH; HAp); moreover, the charges of sub-millicoulomb order could be stored in the polarized Sr-HAp. The results of in vitro characterization of polarized Sr-HAp ceramics were comparable to those observed on HAp with high biocompatibility, showing the acceleration of bone-like crystal growth on negatively charged ceramic surfaces by electrical polarization. These findings provide evidence that the surface charge of these apatite materials with hydroxide ions promotes the biological reaction.