of biomaterials and biocompatibility. The performance of The formation of protein layers during competitive adsorption any foreign material in contact with biological fluids (e.g., was studied with ellipsometry. Single, binary, and ternary protein blood) is believed to depend on the proteins adsorbing at its solutions of human serum albumin (HSA), IgG, and fibrinogen surface (1-4). The main reason for this is that the adsorbed (Fgn) were investigated at concentrations corresponding to blood proteins are able to trigger defense mechanisms (e.g., the plasma diluted 1/100. As a model surface, hydrophobic hexamethcomplement activation and the coagulation cascade) in yldisiloxane (HMDSO) plasma polymer modified silica was used.
blood when they undergo certain changes on contact with By using multiambient media measurements of the bare substrate the surface. Considering this, there have been numerous efprior to protein adsorption the adsorbed amount as well as the forts to develop biomaterial surfaces which either do not thickness and refractive index of the adsorbed protein layer could be followed in situ and in real time. Under conditions used in adsorb serum proteins at all, or which adsorb biologically these experiments neither IgG nor fibrinogen could fully displace ''inactive'' serum proteins, e.g., albumin, preferentially.
serum albumin from the interface. The buildup of the protein
In the development of selectively adsorbing biomaterials, layer occurred via different mechanisms for the different protein there is a need to understand the competitive adsorption systems. Fgn adsorbed in a rather flat orientation at low adsorbed occurring from complex protein mixtures, such as blood. amounts, while at higher surface coverage the protein reoriented Therefore, there is a need to be able to study both the adto a more upright orientation in order to accommodate more molesorbed layer structure and the formation, the adsorbed layer cules in the adsorbed layer. IgG adsorption proceeded mainly endcomposition, and the conformation of the adsorbed protein on with little reorientation or conformational change on adsorpmolecules. Until now, several different approaches have tion. Finally, for HSA an adsorbed layer thickness greater than been undertaken in the study of competitive adsorption from the molecular dimensions was observed at high concentrations protein mixtures. Some investigators have studied adsorption (although not at low), indicating that aggregates or multilayers from blood plasma using antibodies to detect adsorbed proformed on HMDSO plasma polymer surfaces. For all protein mixtures the adsorbed layer structure and buildup indicated that Fgn teins of particular importance for the biological response. In was the protein dominating the adsorbed layer, although HSA this context the pioneering work by Vroman (4) should be partially blocked the adsorption of this protein. At high surface mentioned. Other investigators have studied less complex concentration, HSA/Fgn mixtures show an abrupt change in both systems such as binary and ternary protein mixtures, using adsorbed layer thickness and refractive index suggesting, e.g., an different techniques based on either solution depletion (5, interfacial phase transition of the mixed protein layer. A similar 6) or surface analysis (4, 7, 8). Studies of this type have but less pronounced behavior was observed for HSA/IgG. For IgG/ mainly been concerned with the adsorbed layer composition. Fgn and HSA/IgG/Fgn a buildup of the adsorbed layer similar to Very few studies contain detailed information on the structhat displayed by Fgn alone was observed.