Osteoblast-like cell response to bioactive composites-surface-topography and composition effects.

Two bioactive composites, containing 40 vol % filler in high-density polyethylene (HDPE), were investigated to examine the effects of different filler compositions and different surface patterning. The first composite, known as HAPEX, consists of hydroxyapatite within HDPE, and the second composite, known as AWPEX, consists of glass-ceramic apatite-wollastonite in HDPE. Surface topography effects at 5-50 and 100-150 microm were explored, with cell morphology analyzed with the use of scanning electron microscopy and confocal laser scanning microscopy (CLSM). Biochemical assays of adenosine triphosphate and alkaline phosphatase were used to analyze osteoblast-like cell proliferation and differentiation. For both composites, cell alignment was seen along grooves, pillars, and wells, with preferential cell attachment to ceramic particles within the polymer matrices. HAPEX showed significantly increased cell proliferation over AWPEX (P < 0.005). However, greater cell differentiation occurred for AWPEX over HAPEX (P < 0.005). Polishing significantly increased osteoblast-like cell response over as-cut samples, but surface-topography changes above 50 microm had no consistent effect. Smaller-scale features also showed no significant trend in terms of cell proliferation, but did show significant differences in cell differentiation (P < 0.05). CLSM imaging of actin and vinculin localization within cells showed the greatest change in comparison to polished surface controls for cells cultured on samples with surface features below 50 microm. The fact that similar observations were made for both HAPEX and AWPEX indicated that, for these experiments, the effects of surface topography more strongly influenced cell response than chemical composition.