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.