Influence of electron-beam irradiation on in-vitro hydrolytic degradation of biodegradable polymer

Abstract

Glaucoma is a group of ocular disease where the fluid pressure is elevated beyond the limit, causing irreversible damage to the optic nerve which eventually leads to a loss of vision. Glaucoma Drainage Device (GDD) is implanted when other medical treatments were ineffective in managing the disease. To avoid post-surgery complication of hypotony and ocular hypertension, a biodegradable valve is to be integrated into the GDD. The biodegradable material for the valve will be required to retain its mechanical properties for the first few weeks after surgery and yet fully disintegrate after 6 weeks. Therefore, the influence of electron-beam (e-beam) irradiation of in-vitro hydrolytic degradation of poly(DL-lactide-co-ε-caprolactone) 70/30 (PLC) were studied in this report. Solvent-casted PLC films were irradiated at 10, 20 and 30 Mrad. Subsequently, PLC samples were immersed in phosphate buffer saline (PBS) solution and incubated at 37ºC for a period of 6 weeks. Several characterization tests were carried out weekly to understand the degradation behavior. Upon e-beam radiation on PLC, Mn of PLC decreases. Despite a decrease in Mn with increasing radiation dosage, ΔHm and Tg decreased gradually. This is due to the combined effect of chain scission and crosslinking initiated by e-beam radiation. At 10 and 20Mrad e-beam radiation, crosslinking predominates and hence, tensile strain and Young’s modulus of PLC increased slightly. However, at higher e-beam radiation dosage of 30 and 40Mrad, chain scission predominates which results in a decrease in tensile strain and significant drop of Young’s modulus to less than 2.5MPa. During 6 weeks of degradation, molecular weight, tensile strain and Young’s modulus of non-radiated and radiated PLC had an overall decrease. The molecular weight and Young’s modulus was affected by the efficiency of oligomer removal. At 10 and 20Mrad, cross-linking predominates and hence oligomers are not removed from PLC. However, at 30 and 40Mrad, chain scission predominates and thus, oligomers were efficiently removed. In conclusion, PLC radiated at 20Mrad displayed unique characteristics such as retention of Young’s modulus in the first few weeks of degradation and difference degradation mechanism from other PLC samples.