MIT20_441JF09_lec11_iy - Methodology for Measuring Surface...

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Methodology for Measuring Surface Ligand Density Prof. Ioannis Yannas 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. Assays of proteins adsorbed on biomaterials surfaces have been developed using increasingly sophisticated physicochemical instrumentation. Extensive use has been made of time of flight secondary ion mass spectrometry (Henry et al., 2008; Michel et al., 2005; Wagner, Shen et al., 2003; Wagner, McArthur et al., 2002; Lhoest et al., 2001); X-ray photoelectron spectroscopy (Henry et al., 2008; Michel et al., 2005; Wagner, McArthur et al., 2002); nuclear labels, such as, 125 I (Zhang and Horbett, 2008; Jenney and Anderson, 2000); and electron spectroscopy for chemical analysis (Wagner, Horbett et al., 2003), among others.
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In these studies the methodological focus appears to be identification of the proteins adsorbed on the surface to which cells adhere, as well as measurement of the protein mass adsorbed, rather than a quantitative study of surface ligand density responsible for cell adhesion. In many studies a major objective of studies of protein adsorption on surfaces has been to improve understanding of in vivo response of biomaterials surfaces to substances such as blood. For example, in one study the adhesion of platelets on 2D polystyrene surfaces that had been pretreated to adsorb fibrinogen was studied with methodological emphasis on assaying the mass of adsorbed protein and identification of sites involved in platelet binding (Tsai et
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This note was uploaded on 11/11/2011 for the course BIO 2.797j taught by Professor Matthewlang during the Fall '06 term at MIT.

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MIT20_441JF09_lec11_iy - Methodology for Measuring Surface...

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