Effects of Sterilization on Shape Memory Polyurethane Embolic Foam Devices
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Shape memory polymer (SMP) foams have been developed for various embolic applications. These polyurethane materials can be deformed and stored in a secondary shape, from which they can recover their primary shape after exposure to an external stimulus, such as heat and moisture. Tailored actuation temperatures of SMPs provide benefits for minimally invasive biomedical applications, but incur significant challenges for SMP-based medical device sterilization. Most sterilization methods require high temperature and/or humidity to effectively reduce the bioburden of the device, but the environment must be tightly controlled after device fabrication. Here, three probable sterilization methods: non-traditional ethylene oxide (ntEtO) gas sterilization gamma irradiation, and electron beam (ebeam) irradiation were investigated for SMP-based embolic medical devices. SMP foam was tested for changes in thermal properties using differential scanning calorimetry. Mechanical testing was used to analyze sterilization-induced material changes. Unconstrained expansion profiles were obtained to see if sterilization affected the shape memory properties of the foam. Finally, spectroscopy was done to analyze potential molecular changes in the foams. Thermal characterization of the sterilized foams indicated that ntEtO gas sterilization decreased the glass transition temperature. Gamma irradiation was hypothesized to generate oxidative radicals that threaten the biostability of the embolic medical device. Further material characterization was undertaken on the ebeam sterilized samples, which indicated minimal changes to foam integrity and device functionality.
Muschalek, Rachael Lee (2017). Effects of Sterilization on Shape Memory Polyurethane Embolic Foam Devices. Master's thesis, Texas A&M University. Available electronically from