Polarization of hydroxyapatite: influence on osteoblast cell proliferation

Hydroxyapatite (HA) has been used clinically to treat bone defects. However, modifications of the surface properties of HA could improve and control bone matrix deposition and localized host tissue integration. The aim of this study was to investigate the effect of developing a surface charge on HA discs with respect to osteoblast activity in vitro. HA discs (12 mm x 2 mm) were sintered in either air or water vapour. The HA discs were then electrically polarized (positive and negative surfaces) or non-polarized (controls) and seeded with MC3T3-E1 cells. Polarized HA sintered in water vapour was shown to retain six times more charge than polarized HA sintered in air. Picogreen analysis demonstrated that at 4h cell number was significantly higher on the negatively and positively charged HA surface (water sintered) in comparison to the non-charged water and air-sintered HA controls. At 7 days there was a significant increase in cell number on the negatively charged HA (air sintered) sample in comparison to the negatively charged water vapour sintered HA sample and the non-charged water vapour sintered control sample. Also at 7 days, the picogreen data showed a significant increase in cell number on the positively charged water-treated HA sample in comparison to both the air- and water-treated HA non-charged control HA samples. An alamarBlue assay at 7 days demonstrated significant cell metabolic activity on the charged surfaces (both positive and negative) in comparison to the non-charged HA and the tissue culture plastic controls. This study demonstrated that all of the HA discs tested supported cell viability/attachment. However, cell attachment/proliferation/metabolic activity was significantly increased as a result of developing a charge on the HA surface.