Beneficial effect of sulfonated PEO-grafted polyurethanes on calcification and lipid adsorption of vascular implants

Abstract

Polyurethane (PU) has been used in many industrial applications as well as in clinics for a wide variety of biomedical applications, because of its good physical properties and physiological acceptability. However, its performance for a long-term implantation is hampered, due mainly to the incomplete blood compatibility. Moreover, PU is degraded due to the leakage of additive and low molecular weight fraction, depolymerization, bond and side group change, and residual stress. For the improvement of the biocompatibility and biostability of PU, numerous attempts have been made via surface and bulk modifications. Meanwhile, calcification, defined as the deposition of calcium compounds such as calcium phosphate, causes the loss of the flexibility of biomaterials, ultimately resulting in their mechanical failure and degradation. Therefore, the prevention of such phenomenon is critical for a long-term safety so that many investigations have been carried out minimize biomaterial calcification. On the other hand, the interactions between lipids and material surface have been frequently neglected because of their instability in solution. However, since the degradation of Silastic heart valves was related to the adsorption of lipid from the blood, their effects on the blood-contacting materials was studied, focusing on the formation and propagation of cracks and on the initiation of atherosclerosis and calcification. Previous studies indicated that PU could initiate the stress cracking by the adsorption of lipids, such as cholesterol and cholesteryl acetate onto the surface. It is believed that the adsorption of cholesterol to implant surface can negatively influence their long-term biostability and performance. In our previous works, a sulfonated poly(ethylene oxide)-grafted PU (PU-PEO-SO3) showed excellent biocompatibility, due to the synergistic effect between hydrophilic, dynamic mobility of pendant PEO chains and electrical repulsion exerted from negatively charged sulfonate groups. In addition, PU-PEO-SO3 enhanced blood compatibility, biostability, and anticalcification as compared to the untreated PU in a rodent subdermal and canine blood contact system. Therefore, based on these results, this study aims to elucidate further correlation between in vivo biocompatibility, especially biostability, calcification, and lipid adsorption and sulfonated PEO-grafted PU using a canine model.