Studies on cell-biomaterial interaction: role of tyrosine phosphorylation during fibroblast spreading on surfaces varying in wettability.

In a previous study we observed that protein tyrosine phosphorylation was significantly diminished in the focal adhesions of human fibroblasts attached on a hydrophobic surface in comparison with hydrophilic glass. This result raises the possibility that the tyrosine phosphorylation pathway may be involved in the regulation of cell-biomaterial interaction. To learn more about the interaction of anchorage-dependent cells with biomaterials, four different materials with wettability ranging from hydrophilic (water contact angle 25 degrees) to hydrophobic (water contact angle 111 degrees) were investigated, i.e. clean glass (glass), aminopropylsilane (APS), octadecylsilane (ODS) and silicone (SI). Immunofluorescence microscopy revealed increased stress formation and fibronectin (FN) receptor-rich focal adhesions for fibroblasts attached on more hydrophilic surfaces (glass and APS) in comparison to the relatively hydrophobic materials (ODS and SI). Phosphorylation of tyrosine residues, also studied by immunofluorescence microscopy, was considerably higher on glass and APS, lower for ODS, negligible for SI, and was found to colocalize with FN receptor-rich focal adhesions. Preadsorption of FN tended to restore cell adhesion and spreading on the hydrophobic ODS and SI. Quantitative data on cell proliferation and tyrosine phosphorylation showed moderate wettable material maximum values for APS, followed by glass. ODS and SI, demonstrating a non-linearity of these parameters with the wettability of materials. Interestingly, the preadsorption of FN increased both parameters, particularly for the hydrophobic materials ODS and SI. Phosphorylation of tyrosine on FN-coated substrata was corroborated by the accessibility of binding sites estimated by ELISA using polyclonal and monoclonal FN antibodies. Our results suggest that measurement of the phosphotyrosine activity of cells may be a sensitive parameter for the ability of biomaterials to support the attachment and proliferation of cells.