Part I. Viscoelastic properties of random copolymer at air/water interface and the frequency dependence. Part II. Magnetic resonance imagible surface of medical devices and its biocompatibility

The static and dynamic properties of random copolymer of poly(tert-butyl methacrylate)-co-poly(methacrylic acid) (PtBMA/PMAA) and homopolymer PtBMA were studied at the air/water interface using the Whihelmy Plate Technique and Electrocapillary Wave Diffraction (ECWD). The collapse pressure of the random copolymer is about 2mN/m higher than the homopolymer reflecting the effect of hydrophilic PMAA. In the collapse region, the viscoelasticity of the random copolymer shows no frequency dependence, whereas the homopolymer exhibits the relaxation controlled by reorientation mechanism. By studying the frequency dependence of viscoelasticity of poly(ethylene oxide) (PEO), poly(vinyl acetate) (PVAc), PtBMA and random copolymer PtBMA/PMAA, we reached a proposal that relaxation processes before and after collapse were controlled by the diffusion and the reorientation mechanism, respectively.; Medical grade polyurethane films were surface modified by hydrazine plasma treatment followed by surface chemical reactions to graft MRI contrast agent, the complex of diethylenetriaminepentaacetic acid and gadolinium ion (DTPA-Gd). All the surface modification procedures were characterized by X-ray photoelectron spectroscopy (XPS), contact angle and atomic force microscopy (AFM). It was demonstrated that the surface density of contrast agent could be increased significantly by grafting. Thus, polyurethane films could be visualized by magnetic resonance imaging (MRI) in yogurt, blood and saline. Other techniques including hydrogel coating and layer-by-layer polyelectrolyte deposition to introduce contrast agent to the surface of medical devices were explored and compared. It is confirmed that the product of relaxivity and concentration of contrast agent is critical for imaging enhancement of medical devices.; The BSA adsorption to the modified PU films was determined using the technique of Quartz Crystal Microbalance (QCM), and a two-state model is proposed to describe BSA adsorption kinetics. It was demonstrated that grafting PEO to the surface was an effective way to make the surface protein adsorption resistant. Through this model, it was found that the ratio of denaturation rate constant to de-sorption rate constant is the most important factor for resisting protein adsorption.