Piezoelectricity in Poled Hydroxyapatite Ceramics

Abstract

Direct current electrical poling of textured hydroxyapatite (HAp) ceramics is reported here to exhibit weak ferroelectricity and pyroelectricity, but a remarkably higher (six orders of magnitude) piezoelectricity. The piezoelectric strain coefficient is an order higher than that of bone and of the same order as that of quartz crystal and uncalcified collagen in tendon. The piezoelectric charge coefficient is an order higher than bone, and three orders higher than that of tendon. Piezoelectric constants of poled HAp ceramics are high enough to have physiological relevance such as in the use of bone grafts for stimulated calcification or in energy harvesting from physiological motions. Piezoelectricity in these ceramics can be tuned by controlling texture, and poling parameters. The density of power that can be harvested from HAp ceramics is currently just one order lower than biocompatible ferroelectric ceramic such as barium titanate.

Electrical properties of hydroxyapatite

“…Much more significant piezoelectricity, as high as six orders of magnitude higher than that measured as shear piezoelectricity, has been obtained recently in textured hydroxyapatite ceramic that was poled under much higher electric field but at relatively lower temperature, 95 °C [11]. The piezoelectric strain coefficient, d33, is an order higher than that of bone and of the same order as that of quartz crystal and uncalcified collagen in tendon.…”

Calcium orthophosphate bioceramics

“…Occasionally, an interest to both electric/dielectric [304,[377][378][379][380][381][382][383][384][385][386][387][388][389][390] and piezoelectric [391,392] properties of CaPO 4 bioceramics is expressed. For example, a surface ionic conductivity of both porous and dense HA bioceramics was examined for humidity sensor applications, since the room temperature conductivity was influenced by relative humidity [378].…”

Hydroxyapatite‐barium titanate piezocomposites with enhanced electrical properties

“…Hydroxyapatite (HA) is one of the widely used synthetic material for bone graft substitutes. 7 Synthetic nanocrystalline HA has recently been demonstrated 8 to exhibit piezo, pyro and ferroelectric property. A.Gandhi et al 8 reported that a combination of optimized poling conditions and texture in HA has resulted in a longitudinal piezoelectric strain co-efficient that is one order higher than that of bone and of the same order as that of the uncalcified collagen in the tendon.…”