Surface Electric Fields Increase Osteoblast Adhesion through Improved Wettability on Hydroxyapatite Electret

Osteoblasts are susceptible to the surface characteristics of bioceramics and stimulation from outside the cells. The purpose of this study was to evaluate the effects of electrical polarization on surface characteristics and osteoblastic adhesion. The surface characteristics revealed that electrical polarization had no effect on the surface roughness, crystallinity, and constituent elements. According to contact-angle measurements, electrically polarized hydroxyapatite (HA), which provides two kinds of surfaces, negatively charged HA (N-HA) and positively charged HA (P-HA), was even more hydrophilic than that of normal HA (O-HA). Morphological observations and quantitative analyses revealed that the typical adhered cells had a round shape on O-HA but had a spindle or fanlike spreading configuration on N-HA and P-HA 1 h after seeding. After 3 h of cultivation, the rate of the number of spread cells and the size of the focal adhesions on O-HA increased and approached that of N-HA and P-HA. However, the cell areas positively stained for actin, which indicates the degree of cell spreading, were distinctly larger on N-HA and P-HA than that on O-HA. The number of focal adhesions per cell was also less than that on N-HA and P-HA.