SUMMARY: The ethylene oxide (EO) mobility in polystyrene-graft-[poly (ethylene oxide)] (PS-g-PEO) and polystyrene-graft-[stearyl poly [(ethylene oxide)] (PS-g-SPEO) copolymers was evaluated by spin probe techniques. The ESR spectra indicate that 4-hydroxyl-TEMPO (TEMPO=2,2,6,6-tetramethylpiperidine-N-oxyl) is strongly biased to the PEO phase of the PS-g-(S) PEO membranes. The rotational correlation time sc can also be employed to assess the PEO mobility in PS-g-(S) PEO membranes. Although sc of PS-g-(S) PEO usually decreases with increasing surface density of EO, it is of interest that sc is ather high when the surface within a depth of at least 5nm is fully occupied by SPEO (sample PS-g-SPEO-72. 6).

A tri-block-coupling polymer, "PEO-MDI-PEO" ["poly (ethylene oxide)-4,4'-methylene diphenyl diisocyanate-poly (ethylene oxide)", abbreviated "MPEO"], was used to react with a triazine dye, Cibacron Blue F3G-A (ciba), in an alkaline environment. The product of this nucleophilic reaction was a penta-block-coupling polymer, "ciba-PEO-MDI-PEO-ciba" (abbreviated "cibaMPEO"). The cibaMPEO-modified poly (ether urethane) (PEU) surfaces were prepared by dip-coating and detected by XPS. The surface enrichment of both ciba endgroups and poly (ethylene oxide) spacer-arms was revealed. On the modified surfaces, bovine serum albumin (BSA)-adsorbing experiments were carried out, respectively, in the low and high BSA bulk-concentration solutions, and accordingly, the methods of radioactive 1251-probe and ATR-FTIR were, respectively, employed for the characterization. The competitive dsorption of BSA and bovine serum fibrinogen (Fg) in the BSA-Fg binary solutions was also studied using a 125I-probe, and through which the reversibly BSA-selective adsorption on cibaMPEO-modified PEU surfaces was confirmed. Finally, the improvement of blood-compatibility on the modified surfaces was verified by the plasma recalcification time (PRT) test.

A coupling polymer, abbreviated SPEO-MDI-SPEO (MSPEO), was synthesized by a simple reaction between 4,4'-methylenediphenyl diisocyanate (MDI) and stearylpoly (ethylene oxide) (SPEO, Mn l900), and the blended poly (ether urethane) (PEU) films of PEU-MSPEO were prepared by a solution process. According to the analysis of ATR-FTIR, it was proved that when MSPEO was blended into the PEU matrix, the middle blocks (M-block) of MSPEO could incorporate with the hard blocks of PEU chains through the linkage of a H bond, leading to the improvement in the blending stability. The surface modification was finally accomplished by the self-motion of MSPEO since the elastomeric property of the matrix permits the modifiers to move freely. In the case of air, due to the relatively poor compatibility and rather low surface energy of the stearyl end groups, they migrated to the polymer-air interface, and thus the connected PEO chains were also enriched there by the tow of the end groups. However, in the case of water, the hydrophilic PEO chains migrated to the outermost layer of the surface, and finally they were enriched on the polymer-water interface, while the hydrophobic stearyl end groups would bend down back into the surface. Therefore, a PEO chain-loop structure was finally formed. Furthermore, also based on the mechanism of self-motioned surface modification, even if a part of MSPEO on the surface would have been washed away by water, the continuous makeup from the bulk would still be able to maintain the quantity of the PEO chains on the interface for a long time. All the results were verified by 1H NMR, ATR-FTIR, XPS, and contact angle measurements.

Chitosan as an antibacterial agent and heparin as an anti-adhesive agent were alternatively deposited onto aminolyzed poly (ethylene terephthalate) (PET) films to construct anti-adhesive and antibacterial multilayer films. The contact-angle and UV data verified the progressive buildup of the multilayer film by alternate deposition of the polyelectrolytes. The properties of multilayer films were investigated by contact angle, atomic force microscopy (AFM), lateral force microscopy (LFM) and UV spectra. The results of initial adhesion of Escherichia coli (E. coli) on PET substrates showed that the number of E. coli adhered onto the control PET was in a much greater extent than onto the chitosan/heparin multilayer films, and the number of adhesive bacteria decreased with a decrease in assembly pH. The in vitro antibacterial test indicated that a multilayer of chitosan/heparin could kill the bacteria effectively. The number of viable bacteria decreased by 7% after 7h in contact with the control PET films, but by 46-68% for the multilayer-modified PET films. Only 3-8% of the cells were viable for the multilayer-modified PET films after 24 h. It is interesting to find the assembly pH has a remarkable effect on the antibacterial property of the multilayer. The number of viable bacteria on the multilayer assembled at pH1/4 3.8, 2.9 and 6.0 decreased by 68%, 58% and 46%, respectively. Such an easy processing and shape-independent method to prepare an anti-adhesive and antibacterial surface may have good potential for surface modification of cardiovascular devices.

Multilayer films consisting of polyethylenimine (PEI) and heparin were successfully prepared on biomedical 316L stainless steel surface via electrostatic self-assembly (ESA) of the PEI and heparin. The process of ESA of PEI/heparin was monitored bystatic contact angle, electrochemical impedance spectroscopy (EIS), reflection adsorption spectroscopyand X-rayphotoelectron spectroscopydata. The contact angle and EIS data revealed that the multilayer coating was stable in Tris-HCl (pH7.35) buffer solution for 21 days. The static platelet adhesion and static clotting time experiments indicated that the PEI/heparin-deposited stainless steel could resist the platelet adhesion and prolong the static clotting time effectively. Such an easy processing and shapeindependent method mayhave good potential for surface modification of cardiovascular devices.