Glass and metal surfaces derivatized with self-assembled monolayers: Cell type-specific modulation of fibronectin adhesion functions

Methods were developed to chemically derivatize glass, titanium, and germanium surfaces with a covalently-linked, siloxane-anchored, and ordered thin film of functionalized organic molecules (self-assembled monolayer). Monolayers are comprised of a 14-17 carbon aliphatic chain terminating with one of many different chemical endgroups. The following endgroups were analyzed - [CH₃], [C=C], [Br], [CN], [Diol], [COOH], [NH₂], [SH], [SCOCH₃], and [SO₃H]. Plasma fibronectin (FN) adsorbed as effectively to all derivatized surfaces as to underivatized surfaces. Mouse 3T3 fibroblasts and Platt human neuroblastoma cells attached equivalently to all surfaces preadsorbed with FN, indicating the availability of receptor binding sites on adsorbed FN molecules. In contrast, transmembrane signaling from FN_adsorbed:Receptor_{cell surface} complexes yielded a range of abilities for generating F-actin stress fibers within fibroblasts, as well as neurite extensions from the neuroblastoma cells. Efficiency patterns on these various substrata for stress fiber formation were very different from the patterns of neurite extension. In addition, the same chemical endgroup on glass, titanium, or germanium yielded the same cellular physiological responses, indicating that the inert substratum cannot act at a distance and that the chemical endgroup regulates FN functions in adhesion. When adhesion-inert albumin is co-adsorbed with FN, efficiency of neurite extension can be greatly improved on some surfaces or diminished on other surfaces. These and other results indicate that these two cell types use different receptors interacting with different binding sites on FN_adsorbed to mediate their transmembrane signals and that the conformation of FN_adsorbed changes in specific ways on derivatized substrata. This latter hypothesis was confirmed by FTIR/ATR spectroscopy experiments of FN_adsorbed. These studies indicate cell type-specific changes in FN conformations on chemically-derivatized self-assembled monolayers leading to up- or down-regulation of specific cellular physiological responses from receptors. They also offer optimism for regulating responses of specific cell types when various cell types interact with biomaterial implants in situ.