Impact of structure, crystallinity, and irradiation modality on post-irradiation free radical evolution in PEs

Polyethylene (PE) has many advantages as a polymeric material for biomedical applications, including single-use (SU) medical ones. Depending on the type of PE, its applications vary from single-use medical device packaging to implants for joint prostheses and custom-made artificial bones. The need to sterilize these products has led to more intensive use of different modalities of high-energy radiation (gamma, electron beam (EB), and X-ray) due to heat input limitations and EtO toxicity.

In this paper, we investigate the effects of gamma and electron beam (EB) radiation on various PE types (LDPE, LLDPE, HMWPE, UHMWPE, and HDPE), focusing on how the initial structure and crystallinity influence post-irradiation behavior and the evolution of long-lived free radicals. Long-lived free radicals were monitored for up to six months, with their evolution correlated to the initial structure and crystallinity. Chain scission, oxidative degradation, and decline in properties caused by long-lived free radicals can continue long after irradiation, significantly impacting performance during storage and even failure of medical devices during exploitation. This article establishes a good correlation between crystallinity and post-irradiation evolution of long-lived free radicals, with limited consideration of other structural features and the presence of additives.