Yinping Zhong

Fluorocarbon chain end-capped poly(carbonate urethane)s as biomaterials: blood compatibility and chemical stability assessments.

Previous work has shown the synthesis of fluorocarbon chain (CF(3)(CF(2))(6)CH(2)O-) end-capped poly(carbonate urethane)s (FPCUs) and confirmed the presence of a novel bilayered surface structure in FPCUs, that is, the top fluorocarbon and subsurface hard segment layers (Xie et al., J Biomed Mater Res Part A 2008; 84:30-43). In this work, the effects of such surface structure on blood compatibility were investigated using hemolytic test and platelet adhesion analysis. The chemical stability of the polymers was also determined by Zhaos glass wool-H(2)O(2)/CoCl(2) test and phosphate-buffered saline (PBS, pH = 3.1-3.3) treatment. One of the FPCUs, FPCU-A, and two control materials, a poly(ether urethane) (PEU) and a poly(carbonate urethane) (PCU), were investigated. No significant difference in hemolytic indices was observed among the three materials, whereas the adherent density and deformation of platelets were much lower on FPCU-A compared with on PCU and PEU. Severe surface cracking and surface buckling developed in prestressed PEU and PCU films after H(2)O(2)/CoCl(2) treatment, respectively, whereas smooth surface was observed for the FPCU-A. PBS incubation resulted in parallel ridge-like morphology in PCU whereas PEU and FPCU-A retained their smooth surfaces. Under relatively high stress conditions, all the materials developed well-oriented strip-like surface patterns. Results from ATR-FTIR spectra revealed a surface oxidation mechanism as described in literature. However, observations of universal decrease of molecular weights under stress conditions further suggested the presence of another bulk stress oxidation mechanism. Regardless the degradation mechanisms involved, the unique bilayered surface structure really improved the blood compatibility and chemical stability of FPCU-A, indicating that further in vivo investigations are worthwhile.

LARGELY IMPROVED BLOOD COMPATIBILITY OF POLYURETHANE BY BLENDING WITH FLUORINATED PHOSPHATIDYLCHOLINE POLYURETHANE

The improvement of biocompatibility of polyurethanes was investigated. The results demonstrate that the blood compatibility of polyurethanes can be further improved by just simply mixing with the fluorinated phosphatidylcholine poly(carbonate urethane)s (FPCPCUs). The solution blending was done by mixing poly(ether urethane) (PEU) with FPCPCU in different compositions. An increased blood compatibility of the blend films was observed with the increase of FPCPCU content, and when FPCPCU content reached to 40 wt% (40FPCPCU film), 6 times and 23 times decrease of platelet adhesion number have been achieved, compared with that of FPCPCU and PEU, respectively. More interestingly, the blend films showed even better blood compatibility than that of FPCPCU. DSC, AFM and XPS were used to characterize the miscibility and surface structure of the blends film. The largely improved blood compatibility was rationalized based on the combined effect of phase separation between PEU and FPCPCU and the formation of surface nanostructures induced by segregation of FPCPCU at the surface.

Prenatal developmental safety of functional polyurethanes for cardiovascular implants

Historically, polyurethanes have been regarded as promising materials for cardiovascular implants such as vascular grafts and heart valves. Their biocompatibility has been thoroughly investigated. However, their developmental toxicity is seldom reported. We recently developed two polycarbonate urethanes with polyethylene glycol side chains capped with epoxy or amino groups that can further react with specific biomolecules. Both materials in microfibrillar morphology were subjected to saline extraction at 70 °C to prompt material hydrolysis. Proton nuclear magnetic resonance, Fourier transform infrared spectroscopy, and gel permeation chromatography all confirmed the degradation of the polyurethanes. The saline extracts containing the degradation products were administered to Sprague-Dawley female rats on day 7 to 16 of gestation via tail vein injection at a dose of 5 mL/kg/day. No maternal toxicity was observed. No external, skeletal, and visceral malformations in fetuses were found associated with the test materials, implying their safety to both adult rats and the offspring. Further investigations for applications in vascular grafts are under way.