Radiation degradation and stability of polyurethanes

Complete text of publication follows. Polymeric biomaterials might be exposed to ionising radiation in order to improve their properties or to carry out sterilization that may also contribute in changes of the macroscopic features. It is generally known that irradiation affects physicochemical and mechanical properties of polymers leading usually to crosslinking and/or degradation. Crosslinking transforms a linear polymer into a tree dimensional network in resulting improvement of mechanical properties. The decrease in molecular weight is a consequence of degradation and leads to deterioration of polymer properties. A proportion between both processes determines final effect. Polyurethanes are a well-known class of polymers with the characteristic -NH-CO-O- linkage in the chain. They are block copolymers, which physicochemical properties may be modified by changing the ratio between soft and hard segments. Type and proportions between segments determine the character of polymer and consequently their industrial utility. Polyurethanes are known as radiation stable materials but their behaviour upon the exposure to ionising radiation is strongly dependent on their chemical and physical structure. Segmented polyurethanes have found application in medicine as biomaterials due to good biocompatibility, hydrolytic and oxidative biostability, excellent mechanical properties and good processibility. They are used for production of scaffolds in tissue engineering and for manufacturing medical devices, such as vascular grafts, artificial hearts, catheters and mammary implants. The aim of this study was to characterize influence of ionizing radiation on the selected physicochemical properties of polyurethanes. Samples of polyurethanes were investigated before and after irradiation by EPR, DSC, TG, gas chromatography, measurement of dynamic contact angle and mechanical properties. On a basis of the study we found that radiation sterilization has not significant influence on physicochemical properties of segmented polyurethanes and two parallel, competitive processes: crosslinking and chain scission were observed.