Electric polarization and mechanism of B-type carbonated apatite ceramics

B-type carbonated apatite (CAp) ceramics, nonstoichiometric hydroxyapatites (HAp) with carbonate ions (CO32-) substituting for phosphate ions, are the major inorganic components of vertebrate bones. Due to the carbonate substitution, CAp is more biodegradable than HAp and has been expected a next generation biomaterial. We have reported the electric polarization of HAp, and induced stored electric charges and electric fields in poling HAp could promote bone healing. Here, we applied electric polarization to CAp and showed the role of substituted CO32- concentrations in CAp in its electric polarization and polarization mechanisms. We found that the electrical conductivities (sigma) and stored charges (Q) of poling CAp dramatically increased with carbonate ion contents. We also found that CAp showed higher activation energy both for conduction and for depolarization than HAp, even though the values of sigma and Q are much higher than those of HAp. These results suggested that the substitution of a small amount of CO32- for PO43- resulted in a change in the conduction and polarization mechanisms in CAp compared with HAp. Our study showed that the poling CAp has the potential to be a new functional biomaterial with biodegradation and large stored electric charges. (C) 2011 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 99A: 116-124, 2011.