Role of proteins and water in the initial attachment of mammalian cells to biomedical surfaces: A review

Anchorage-dependent mammalian cells are typically grown in vitro on hydrophilic glass and plastic substrata in a medium supplemented with 5-20% v/v blood-serum proteins. Inoculated single cells gravitate from suspension to within close proximity of substrata surfaces whereupon initial contact and attachment occurs followed by progressive cell adhesion, spreading, and ultimately proliferation. A critical examination of the role of proteins and water in the initial attachment phase concludes that the cell attachment phase is not mediated by biological recognition of surface-adsorbed ligands by cell membrane receptors as frequently depicted in various textbook explanations of cell adhesion. This conclusion is based on extensive experimental evidence showing that blood proteins do not adsorb on hydrophilic surfaces that are most conducive to cell growth but do adsorb on hydrophobic surfaces that are not conducive to cell growth. As a consequence, the conventional idea that initial cell attachment is mediated by various adhesin factors adsorbed from serum-protein solutions is viewed as untenable. Rather, it is concluded that the initial contact-and-attachment of cells to hydrophilic surfaces is controlled by physicochemical interactions unrelated to biological recognition. The general physics of these interactions is known but an adequate descriptive theory that can be tested against experimentally measured cell adhesion kinetics has yet to be developed. The role of these physicochemical interactions in stimulating biological machinery within cells to fully adhere and proliferate on surfaces of biotechnical interest is unknown but is of great significance to the science underlying various biomedical and biotechnical applications of materials.