Effect of hydroxyapatite porosity on growth and differentiation of human osteoblast-like cells

To study whether hydroxyapatite (HA) porosity can influence its osteoconductive properties, cell adhesion, proliferation and differentiation were compared in human osteoblast-like cells grown on HA disks of different porosity (A = 20%, B = 40%, C = 60%). Human osteoblast-like cells were isolated and characterized. Proliferation rate and alkaline phosphatase (ALP) activity were assessed at 3, 7, 15, 21, and 28 days. Type I collagen and osteonectin production were demonstrated with fluorescence microscopy and osteoblast adhesion studied at 7 and 21 days by scanning electron microscopic analysis. Cell growth on HA was three- to six-fold lower than on polystyrene control disks. At 28 days, 2141 (±350) cells/well grew on the most porous disks (Group C), with highly significant differences from controls (p <0.005). The ALP production was 2-3 fold lower on HA than on plastic. In the Group C the mean ALP activity was of 2.95 (±0.07) UI/well after 28 days, higher than in the other two groups. At 21 and 28 days, proliferation rate and ALP activity on the three HA cultures were significantly different (p < 0.05). A decrease in cell population and increased ALP activity were observed on the most porous material, and high proliferation and poor differentiation rates on the less porous disks.