Polarization of porous hydroxyapatite scaffolds: influence on osteoblast cell proliferation and extracellular matrix production.

Improvements to clinically used biomaterials such as hydroxyapatite (HA) are of potential benefit to the patient. One modification, the addition of surface charges, has been shown to have an important role influencing cell response. In this study, porous HA scaffolds with both positive and negative surface charges were manufactured. The samples were sintered in air to produce porous HA ceramic scaffolds in the form of cylinders 12 mm in height × 7 mm in diameter. These were polarized with a dc voltage of 3 kV/cm. MC3T3E1 cells were placed on either negative or positive ends of the charged (or unpoled control) HA scaffolds. At 7 days, picogreen analysis was performed to analyze the cell number at the negative (4 mm), central (4 mm), and positive (4 mm) portions of the 12 mm cylindrical scaffold. At 4 weeks, micro-CT analysis was performed to quantify the regional volume of mineralized matrix deposition on the 3D scaffold. At 7 days, there were significantly more cells present at the negative end of the scaffold when seeded from the negative end in comparison to the other samples tested. Micro-CT data at 4 weeks correlated with this finding, demonstrating an increase in mineralized matrix at the negatively charged end of the scaffold seeded from the negative end in comparison to the positively charged and unpoled control scaffolds. The results indicate that the charge on HA influences cell activity and that this phenomenon can be translated to a clinically relevant porous scaffold structure.

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.

Electrical characterization of hydroxyapatite-based bioceramics.

This paper studies the AC conductivity and permittivity of hydroxyapatite (HA)-based ceramics from 0.1 Hz-1 MHz at temperatures from room temperature to 1000 degrees C. HA-based ceramics were prepared either as dense ceramics or in porous form with interconnected porosity and were sintered in either air or water vapour. Samples were thermally cycled to examine the influence of water desorption on AC conductivity and permittivity. Surface-bound water was thought to contribute to conductivity for both dense and porous materials at temperatures below 200 degrees C. At temperatures below 700 degrees C the permittivity and AC conductivity of HA was also influenced by the degree of dehydration and thermal history. At higher temperatures (700-1000 degrees C), bulk ionic conduction was dominant and activation energies were of the order of approximately 2 eV, indicating that hydroxyl ions are responsible for conductivity.