Enhanced osteoblastic adhesion through improved wettability on polarized hydroxyapatite

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 surface roughness, crystallinity, and constituent elements. According to contact angle measurement, electrically polarized 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 the O-HA but had a spindle spreading configuration on the N-HA and the P-HA 1 h after seeding. After 3 h of cultivation, the rate of the number of spread cells on the O-HA increased and approached that of the N-HA and P-HA. However, the cell areas positively stained for actin, which indicates the degree of cell spreading, were distinctly larger on the N-HA and P-HA than that on the O-HA. The number of focal adhesions per cell was also less than that on the N-HA and P-HA. To conclude, the polarization improved the wettability of the HA surface, which consequently affected osteoblastic adhesion, especially spreading.