Polarization effect on wettability of bioceramic electrets

Bioceramic electrets are produced by electric polarization. Above all, polarized calcium hydroxyapatite (HA) ceramics are excellent electrets: HA electrets have a strong influence on the osteoblast behaviors. Osteoblasts are susceptible to the surface characteristics of bioceramics and stimulation from outside the cells. The purpose of this report is to introduce the fundamentals of bioceramic electrets such as the effects of electrical polarization on surface characteristics and osteoblastic adhesion. The surface characteristics revealed that electrical polarization had no effect on surface roughness, crystallinity, and constituent elements. According to contact angle measurement, electrically polarized HA, which provides two kinds of surfaces, negatively charged HA (N-surface) and positively charged HA (P-surface), was even more hydrophilic than that of conventional HA. Morphological observations and quantitative analyses revealed that the typical adhered cells had a round shape on the HA but had a spindle or fan-like spreading configuration on the N-surface and the P-surface 1 h after seeding. After 3 h of cultivation, the rate of the number of spread cells and the size of focal adhesions on the HA increased and approached that of the N-surface and P-surface. However, the cell areas positively stained for actin, which indicates the degree of cell spreading, were distinctly larger on the N-surface and P-surface than that on the HA. The number of focal adhesions per cell was also less than that on the N-surface and P-surface.