In vitro response of osteoblasts to hydroxyapatite-reinforced polyethylene composites

A primary human cell culture model was used to investigate a range of hydroxyapaptite (HA)-reinforced high-density polyethylene (HDPE) composites (HAPEX). These materials are being developed as potential bone-substitute materials. When designing and optimizing a second-generation biomaterial, it is important to achieve a balance between mechanical and biological properties without compromising either. Biochemical and histological parameters have been used to compare the biological response of 20% and 40% volume HA in HDPE. Cellular DNA and incorporation of tritiated thymidine was measured to assess cell proliferation. Alkaline phosphatase (ALP) production was used as a marker of osteoblast phenotype expression. In this preliminary study, osteoblasts cultured on the 20% HAPEX showed a greater increase in the rate of proliferation and osteoblast expression as indicated by an increase in ALP activity compared to the 40% HAPEX over the time period studied. Osteoblast-like cells showed a flattened morphology on both composites and in some cases a greater covering was observed on the 20% HAPEX. These results indicate that the composites may not be identical in terms of bioactivity and that further research on surface topography and physico-chemical properties is required to assess fully the biological response of these composites.