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).

Summary: The multilayers of polycation-based non-viral DNA nanoparticles and biodegradable poly(L-glutamic acid) (PGA) were constructed by a layer-by-layer (LbL) technique. Poly(ethyleneimine) (PEI) was used to condense DNA to develop non-viral DNA nanoparticles. AFM, UV-visible spectrometry, and TEM measurements revealed that the PEIDNA nanoparticles were successfully incorporated into the multilayers. The well-structured, easily processed multilayers with the non-viral DNA nanoparticles may provide a novel approach to precisely control the delivery of DNA, which may have great potential for gene therapy applications in tissue engineering, medical implants, etc.

Thin polymer films were formed on poly-(dl-lactide) (PDL-LA) using polyelectrolyte multilayer technique to promote the chondrocyte cytocompatibility. PDL-LA substrates were activated by poly-(ethylenimine) to obtain stable positively charged surface. The polyelectrolytes such as alginate and poly-(l-lysine) were alternatively deposited onto the activated PDL-LA substrates. The multilayer-modified PDL-LA films were investigated by X-ray photoelectron spectroscopy, attenuated total reflection FTIR, contact angle and atomic force microscopy. The in vitro chondrocyte test indicated that the multilayer-modified PDL-LA substrates promoted chondrocyte attachment and growth. In comparison to conventional coating methods, polyelectrolyte multilayers are easy to prepare and the procedure is valid whatever the shape of the solid. It allows broad medical applications for drug delivery and tissue engineering.

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.