Initial interaction of U2OS cells with noncoated and calcium phosphate coated titanium substrates

From previous studies, we know that calcium phosphate (CaP) coated implants stimulate bone formation compared to uncoated implants. Nevertheless, the mechanism by which substrate surface characteristics affect cell function is unclear. In this study, we examined the initial interaction (30 min to 24 h) of U2OS cells with titanium substrates with or without a CaP coating. The effect of substrate roughness was also studied. When cell attachment was studied, we found that cells attached more readily to rough than to smooth surfaces. Also, more cells attached to the uncoated than to the CaP coated surface. After 24 h, cell numbers were similar for all substrate surfaces. Further, cells spread to a larger area on noncoated titanium than on the CaP coated substrates. At 24 h, the sequence of cell size was smooth titanium > rough titanium > CaP coated titanium. Shape measurements showed differences in cell shape between the cells on the different materials only at 7 h, not at different culture times. Cells expressed alpha2, alpha3, alpha5, alpha6, alphav, and beta1 subunits. Expression of alpha1, alpha4, alphavbeta3, beta3, beta4, and beta7 was extremely low or was not found. The beta1 integrin expression was higher on the coated than on the noncoated titanium at 3 h, but not on the other studied times. Expression of alpha2, alpha5, alpha6, and alphav expression was found to be upregulated at 24 h compared to earlier culture times on coated titanium, but not on uncoated titanium substrates. From this we conclude that the surface characteristics of a material (roughness and composition) can affect the initial interaction of cells with the material.