Methodology for Measuring Surface Ligand Density

What do investigators like to know about the surfaces of their biomaterials? Historically, the focus has shifted from studies of proteins adsorbed on surfaces to assays of surface ligands for cell attachment. Currently, a large number of investigators are interested to find methods for persuading cells to modify their phenotype in order to achieve a useful end result. Typical areas of interest among the biomaterials community are identification of specific substrates that induce a therapy (e.g., block proliferation of cancer cells migrating on substrates) or a tissue-engineering synthesis (e.g., synthesis in vitro of a functional liver organoid) or a desired endpoint in regenerative medicine (e.g., regeneration at the site of a wound, rather than contraction or scar formation). The motivation behind all these diverse pursuits is the rapidly increasing appreciation that insoluble surfaces are capable of changing cell phenotypes. Traditionally, cell regulation has being considered to be the domain of soluble regulators (cytokines, growth factors, hormones). Although insoluble surfaces were known to be capable of having biological activity from studies completed several years ago, the widespread appreciation of this finding is a relatively new development. In the biological and medical communities little attention has been traditionally paid to regulation of cell phenotypes by insoluble, solid-like surfaces. Most of the studies of regulation of cell phenotype by surfaces appear to have historically originated with biomaterials scientists and engineers.