The anticalcification effect of polyethylene glycol-immobilized on hexamethylene diisocyanate treated pericardium

Pathologic calcification is thought to be the main cause of failure in the present generation tissue valves fabricated from glutaraldehyde pretreated bovine pericardium (BP). The present investigation describes the in vitro calcification and enzymatic degradation of bovine pericardia after hexamethylene diisocyanate (HMDIC) crosslinking and subsequent modification with polyethylene glycol. The enzymatic degradation of these treated surfaces were monitored by scanning electron micrography and tensile strength measurements. Various proteases, such as alpha-chymotrypsin, bromelain, esterase, trypsin and collagenase were investigated for tissue stability. Incubation of these enzymes with crosslinked pericardia had variably reduced their tensile strength. Among these treated surfaces, polyethylene glycol (PEG) grafted BP via isocyanate functionalities had retained maximum strength. The PEG modified tissues had also indicated a substantial reduction in calcification, when compared to other treated tissues. Further, the biocompatibility of various pericardial tissues were established by platelet adhesion and octane contact angle measurements. It is assumed that the PEG modification of pericardium may interfere with the cellular activation of injury (platelets) to reduce tissue associated calcification. In conclusion, it seems the PEG modification of bovine pericardium via HMDIC may provide new ways of controlling tissue biodegradation and calcification. However, more in vivo studies are needed to develop applications.