Mechanical Analysis of Thermosensitive Hydrogels for Drug Delivery

Mechanical analysis was conducted on thermosensitive hydrogels to determine their suitability for use in a triggered-release chemotherapy system. Gels were tested in their hydrated state to mimic physiological conditions. Three types of polymer gels were tested: non-responsive in the form of poly(2-hydroxyethyl methacrylate) or PHEMA, negatively thermosensitive in the form of poly(N-isopropylacrylamide-co-acrylamide) or P(NIPAAm-co-AAm), and positively thermosensitive in the form of PHEMA grafted with oligomers of NIPAAm-co-AAm. The PHEMA gels create a good baseline test since they are thermally non-responsive. The negatively thermosensitive gels, based on PNIPAAm, shrink as they are heated turning diffusion off. Positively thermosensitive gels based on PHEMA grafted with oligomers of NIPAAm-co-AAm open to release a drug when heated. Results confirm the shrinking/swelling behavior of the P(NIPAAm-co-AAm) gels and show that the grafted oligomers may alter the physical structure of PHEMA gels. Because drug release rates depend on the structural organization of the polymer mesh, these results will be useful in designing release systems for various chemotherapeutic agents.