Effects of Hydroxyapatite Crystal Morphology on Osteoblast-like Cell Response

Hydroxyapatite (HA) shows promise as a reinforcement phase in synthetic orthopedic bicomposites due to a close resemblance to bone mineral, as well as demonstrated biocompatibility and bioactivity. Polymers reinforced with HA whiskers have exhibited improved bone-like mechanical properties compared to equiaxed HA powders. Preliminary studies have also indicated that HA whiskers are at least as biocompatible as conventional HA powders. Therefore, the objective of this study was to examine the effects of HA crystal morphology on osteoblast-like response in two-dimensional substrates independent of the HA composition, stoichiometry and porosity. The HA crystal morphology affected the substrate surface roughness, which was measured by profilometry. The average roughness of HA whisker compacts was more than twice that of the powder compacts. Specific aims of this study were to quantify and compare osteoblast attachment, viability, proliferation and differentiation in response to HA powder and whisker morphology. MC3T3-E1 osteoblast-like cells were cultured on HA powder and whisker compacts for a period of up to 14 days. Cell attachment, proliferation and differentiation were similar on both substrate types, although spreading was greater on HA whiskers. Proliferation did not increase throughout a seven day culture period; however, cells reached confluence by 14 days in culture on both substrates. These results, in conjunction with the improved mechanical properties of polymer composites reinforced with HA whiskers, establish whiskers as a biomaterial of similar cytocompatibility to conventional equiaxed HA powders and worthy of further study.