Effects of Terminal Sterilization on PEG-Based Bioresorbable Polymers Used in Biomedical Applications.

The effects of ethylene oxide (EO), vaporized hydrogen peroxide (VHP), gamma (γ) radiation, and electron-beam (E-beam) on the physiochemical and morphological properties of medical device polymers are investigated. Polymers with ether, carbonate, carboxylic acid, amide and ester functionalities are selected from a family of poly(ethylene glycol) (PEG) containing tyrosine-derived polycarbonates (TyrPCs) to include slow, medium, fast, and ultrafast degrading polymers. Poly(lactic acid) (PLA) is used for comparison. Molecular weight (Mw) of all tested polymers decreases upon gamma and E-beam, and this effect becomes more pronounced at higher PEG content. Gamma sterilization increases the glass transition temperature of polymers with high PEG content. EO esterifies the carboxylic acid groups in desaminotyrosol-tyrosine (DT) and causes significant degradation. VHP causes hydroxylation of the phenyl ring, and hydrolytic degradation. This study signifies the importance of the chemical composition when selecting a sterilization method, and provides suggested conditions for each of the sterilization methods.

Ethylene oxide's role as a reactive agent during sterilization: effects of polymer composition and device architecture.

Sterilization conditions need to be optimized to effectively neutralize the bioburden while using short exposure times for minimizing the changes in chemical composition, material properties and device architecture. Towards this goal, effects of ethylene oxide (EtO) exposure parameters such as time, temperature, humidity, and EtO concentration on the polymer properties were investigated by monitoring the changes in composition, and the morphology of different types of structures in a family of poly(ethylene glycol) (PEG)-containing tyrosine-derived polycarbonates. EtO was found to esterify the carboxyl groups present in the desaminotyrosyl-tyrosine groups. Sterilization under conditions more severe than those normally used reduced the glass transition temperature (Tg) and the molecular weight of the polymers, and the presence of PEG in the polymer enhanced this effect. Furthermore, electron micrographs showed that EtO sterilization cycle conditions, even those considered "mild," were found to damage the fragile structures such as those found in electrospun mats and porous scaffolds. Our study shows that the presence of EtO-susceptible groups, fusible architecture, and surface morphology should be taken into account in choosing the appropriate EtO sterilization conditions.