Polarized hydroxyapatite promotes spread and motility of osteoblastic cells

Osteoblast adhesion to surfaces of implant substrates is recognized as playing a fundamental role in the process of osteoconduction. The purpose of this study was to evaluate the in vitro adhesion of osteoblasts cultured on polarized hydroxyapatite (HA), which provides two kinds of surfaces; negatively charged HA (N-HA) and positively charged HA (P-HA). Those surfaces have been proved to enhance the osteobonding capabilities. Osteoblastic cells were seeded onto normal and polarized HA; adhesion and motility of each was observed. Polarization did not affect the percentage of the spread cells against all the adhered cells, but had a significant effect on the spreading of each cell as shown by the measured elongation of the adhered cells by fluorescence observation. The elongation of each cell was especially enhanced on the N-HA and P-HA, when compared with normal HA (O-HA). In addition, the polarization affected cell motility shown by wound healing. Motility analysis showed that the same number of cells started to migrate toward the wound areas on each type of surface. However, the migration of each cell type towards the wound area was accelerated on the N-HA and P-HA. The charges induced on the HA surface accelerated the cytoskeleton reorganization of the adhered cells. The acceleration was appeared as cell shape, actin filament pattern such as stress fiber formation, and prolongation of cell motility distance.