Characterization and confirmation of the long lifetime of a-decade-aged hydroxyapatite ceramic electrets

With an aim at long-time use of biocompatible hydroxyapatite (HAp) ceramic electrets as implant devices in-vivo, long-term tracking experiments involving non-destructive surface potential (V_S) measurements over a decade were undertaken to confirm the long lifetime (LT) of HAp ceramic electrets. A-decade-aged HAp electrets maintained their initial as-polarized V_S of ~ 100 V on storage in an oven at warm temperatures (such as 60 ℃). In contrast, the V_S of electrets preserved in air at room temperature gradually reduced after 8 years of aging, retaining the as-polarized value on exposure to heating at 200 ℃; this phenomenon can be ascribed to the shielding effect of moisture on the specimen surface. The long LT of HAp electrets was also confirmed by a destructive measurement technique involving thermally stimulated dissipated currents (TSDC) on decade-aged specimens. Besides confirming the semipermanent LT of HAp ceramic electrets, this study proposes the concept of a grain electret to explain the non-identical surface charge density values derived from V_S and TSDC data. Therefore, this study could open new frontiers in ceramic electret research, paving the way for the widespread practical application of such systems.