Electrical polarization of bioactive glass and assessment of their in vitro apatite deposition.

Abstract

We evaluated the electrical polarizability of a bioactive glass of the 45S5 type (BG) by thermally stimulated depolarization current (TSDC) measurement based on the effects of the surface charges generated by an electrical polarization treatment on the growth of calcium phosphate crystals in simulated body fluid (SBF). From the results of the TSDC measurements, the polarized BG showed broad peaks in the depolarization current density spectra. The stored electrical charges calculated from the TSDC measurements of the BG polarized with an electrical dc field of 10 V x cm(-1) at 500 degrees C for 1 h was 8.5 mC x cm(-2) and depended on the electrical dc field intensity. The depolarization of the BG was assumed to be due to a migration of sodium ions and influenced by transitions of the BG structure. The immersion tests with the SBF showed that the effects of the electrical polarization produced morphologic changes in the calcium phosphate deposit grown on the BG after the short period of 2 h. We expected the effects to be caused by a change in the ion concentrations in the surrounding SBF due to the surface charges of the polarized BG. The change in the ion concentrations induced the difference in the calcium phosphate deposition. Consequently, we confirmed that BG had an electrical polarizability, a possibility of storing large charges, and differences in the growth of the calcium phosphate deposit due to the effects of the surface charges.