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Proteins, Biomaterials and Surface Analysis

David G. Castner
National ESCA and Surface Analysis Center for Biomedical Problems*
Departments of Bioengineering and Chemical Engineering
Box 351750, University of Washington
Seattle, Washington  98195-1750  USA

    The adsorption of proteins onto a biomaterial surface from the surrounding fluid phase is rapid, with the surface properties of the  biomaterial determining the type, amount, orientation and conformation of the adsorbed proteins.  The composition of the adsorbed protein layer (i.e., the type and concentration of the proteins present in the adsorbed film) can differ from the fluid phase composition and can change with time adsorbed.  For example, the initial composition of the protein film formed upon exposure of a biomaterial to blood plasma is typically enriched fibrinogen.  With increasing exposure time, the fibrinogen concentration in the adsorbed film decreases as it is displaced by the other proteins from the blood plasma.  In addition to the time-dependent compositional changes, each absorbed protein can undergo conformational and orientational changes.  Upon adsorption, a protein can retain the conformation or structure it has in the biological environment or it may conformationally change in response to local environments. The nature of the biomaterial surface strongly influences the composition and recognizability of the adsorbed protein layer, which in turn affects the subsequent cellular interactions.  Thus, to understand the biological response to a biomaterial, especially in vitro, one must fully understand the nature of the adsorbed protein film that forms on that biomaterial.
X-ray photoelectron spectroscopy (XPS), static time-of-flight secondary ion mass spectrometry (ToF SIMS), scanning probe microscopy (SPM), and near edge x-ray absorption fine structure (NEXAFS) are some of the surface science techniques that can be used to characterize adsorbed protein films.  XPS provides information about the amount, thickness, and coverage of adsorbed protein films.  Static ToF SIMS combined with multivariate analysis provides information about the type, amount and conformation of adsorbed proteins.  SPM and NEXAFS provide information about the shape and orientation, respectively, of adsorbed proteins.  Using these techniques in a complementary manner can provide the detailed information needed to correlate the surface structure and composition of a biomaterial to the type of protein and cellular interactions that occur with that surface.  Several examples showing how biomaterial surface structure is related to the adsorption of proteins and subsequent cellular reactions will be discussed.  These examples will range from biomaterials that resist protein adsorption [e.g., poly(ethylene glycol)] to those that tightly bind proteins [e.g., fluorocarbons].

*NESAC/BIO is supported by NIH grant RR-01296 from the National Center for Research Resources.
 
 


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