Effect of gamma irradiation and irradiation temperature on hydrolytic degradation of synthetic absorbable sutures

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Abstract
The purpose of this study is to examine the effects of γ irradiation and the relative magnitude of Tirr to Tg on the physical, mechanical, thermal, morphological, and hydrolytic properties of two types of synthetic absorbable polymers. Polyglycolic acid (PGA) and glycolide‐trimethylene carbonate block copolymer fibers in the form of 2/0 size Dexon and Maxon sutures from Davis/Geck were used in this study. In addition, injection‐molded PGA disks were also used for determining how different polymer morphology affected the outcomes of γ irradiation and irradiation temperature. These two types of biomaterials were 60Co γ irradiated at two irradiation temperatures (55 and −78°C in dry ice). Both γ‐irradiated and control speciments were immersed in a phosphate buffer solution of pH 7.44 at 37°C for various durations of hydrolysis. After each predetermined duration, the specimens were removed for subsequent testing which included determinations of tensile strength, weight loss, level of crystallinity, melting temperature, intrinsic viscosity, surface morphology, and infrared spectroscopic characteristics. γ irradiation at both irradiation temperature resulted in a faster hydrolytic degradation of these two biodegradable polymers. There was no apparent irradiation temperature effect in terms of mass loss, intrinsic viscosity, level of crystallinity, and melting temperature. However, irradiation temperature effect was evident in those properties that depended on the tie‐chain segments located in the noncrystalline domains, such as tensile strength. The observed seffect of irradiation temperature was attributed to chain mobility which could facilitate cage recombination of macromolecular radical pairs at the irradiation temperature lower than the glass transition temperature of the irradiated polymers. © 1995 John Wiley & Sons, Inc.