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Electrical and biological properties of polarized hydroxyapatite electrets

Electrically polarized ceramics are classified as electrets, when ions are displaced or dipole moments are aligned in a direction for a considerable period due to an external electric force. An electret can independent irradiate an electrostatic force to the surrounding constituents. As briefly mentioned above, polarization takes place due to the off-centered displacement of cations and anions in the structure of a solid. The centers of these ions are generally difficult to be moved even in a strong dc field because of rigid chemical bonding. Actually, it is true that most ceramics are unsuitable for polarization. The ionic center of a very few materials, however, is liable to off-centered by a dc field and we have experimentally proved that the biocompatible hydroxyapatite (Ca5(P04)3OH; HA) is polarizable material. The polarized HA is an excellent electret which has desirable biological effects upon surrounding alive and non-alive components in vivo as well as in vitro: Using HA electrets, we have observed that crystal growth from a simulated body fluid can be accelerated or decelerated, and microorganism can be manipulated on the surfaces of HA, depending upon the electric signs. Hence we consider that one of the most promising approaches to the innovation in medical technology is use of biomedical electrets. This paper introduces the important electrical properties of HA ceramics.