Studies On The Synthesis And Protein Adsorption Tests Of Biomedical Polyurethane Surfaces

Polyurethanes (PU) have been widely used as an ideal polymer artificial organ due to their excellent physical properties and relatively good biocompatibility, for example artificial heart, catheter intervention, cardiopulmonary bypass devices etc. However, surface induced thrombosis remains a significant challenge for these unmodified PU when in contact with blood. Thus, numerous studies have addressed this deficiency via several types of PU surface modification.1.In this dissertation, heparin-conjugated biodegradable polymers (PU-heparin) and by coupling of heparin to PU through different monomers were successful synthesized and characterized. Double bonds first introduced onto the PU surface through "grafting from" method result in polymerization of PHEMA/PNHSMA to give a PU-PHEMA/PNHSMA film. Then the free-OH groups on PU-PHEMA were transformed to N-succinimidyl carbonate by reacting with N,N-disuccinimidyl carbonate (DSC) to obtain PU-PHEMA-NHS surface; Finally, PU-PHEMA-NHS was coupled to amine of heparin to give PU-PHEMA-Hep surface. At the same time, the PU-PNHSMA film can directly react with heparin to obtain PU-PNHSMA-Hep surface. X-ray photoelectron spectroscopy (XPS) provides evidence for the preparation of modified surfaces at different stages. The result of water contact angle measurement showed that all the modified surfaces were much more hydrophilic than the control surface. In addition, the protein adsorption experiments showed that these surfaces reduced nonspecific protein adsorption efficiently and adsorbed significant quantities of antithrombinâ…¢(ATâ…¢) which can prevent blood coagulation.2. Three new PU having a phospholipids polar group which was connected to various spacers were synthesized, respectively. The phosphorylcholine groups of the modified surface were determined by x-ray photoelectron spectroscopy and water contact angle measurement. As a fundamental evaluation for biomedical materials, the amount of fibrinogen adsorbed on the PU-PC polymer was also evaluated. It was observed that these three surfaces also reduced nonspecific protein adsorption. But the protein adsorption of PC surface increased after a decreasing with the molecular weight of PEG. PEG (Mn=1000) grafted surfaces possessed lower value of protein adsorption than that of other surfaces. We hypothesized that the bridging unit connecting the PC group with the backbone might affect the surface density of the PC group, the mobility of the polymer chain, hydration kinetics and surface enrichment of the PC groups might influence the blood compatibility of phospholipid polymers.