Interactions of polymers and proteins at interfaces studied by sum frequency generation vibrational spectroscopy

The interactions between polymers and proteins have a significant impact on whether a material is biocompatible. The study of these interactions must focus on the behavior of these molecules at the interface. A nonlinear vibrational spectroscopic technique, sum frequency generation (SFG) vibrational spectroscopy, has been used to investigate these surfaces and interfaces. Research focusing on the surface structures of plasticized polyurethanes, commonly used for biosensors, indicates that plasticizers can segregate to the polyurethane surface not only in air but also in water. In addition, plasticizer content can affect the protein adsorption behavior of these surfaces.; An important blood protein, fibrinogen, was adsorbed onto the surfaces of two biomedical polyurethanes and a perfluorinated polymer. Changes in the secondary structure of adsorbed fibrinogen were monitored using attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and SFG. Amide I signals from SFG demonstrate that fibrinogen has post-adsorption conformational changes that are dependent upon the polymer surface properties. This change is not readily observed by ATR-FTIR. Differences in the observed spectral changes for fibrinogen adsorbed to each polymer are explained by different initial binding mechanisms and post-adsorption conformational changes.; Several investigations focused on the surface restructuring of poly(alkyl methacrylates) (PAMAs). Poly(ethyl methacrylate) (PEMA) and poly(ethyl acrylate) (PEA) were found to have quite different surface restructuring behaviors upon contact with water. Though the molecular surface structures in air are similar, PEMA remains a stable film when exposed to water, while PEA delaminates from the substrate surface. The surface reorientation of a series of PAMAs has been deduced. Surface side chain orientation changes of two PAMAs have been observed upon protein adsorption using SFG. Side-chain-deuterated poly(ethyl methacrylate) and poly(n-butyl methacrylate) were contacted with five protein solutions. Adsorption of different proteins to the surfaces resulted in polymer side chains with orientations slightly differing from each other, and in between the air and buffer cases. Finally, a study of the SFG dependence on PAMA film thickness was examined, and optimal experimental conditions are described.