Comparison of properties between NIPAAm-based simultaneously physically and chemically gelling polymer systems for use in vivo.

In this work, a comparison between two different physical-chemical gels, poly(NIPAAm-co-cysteamine) with poly(NIPAAm-co-cysteamine-vinylsulfone) and poly(NIPAAm-co-cysteamine) with poly(NIPAAm-co-HEMA-acrylate), is made. These hydrogels undergo gelation via dual mechanisms: temperature sensitivity (physical gelation) and chemical crosslinking (chemical gelation). The advantages of using both gelation mechanisms are to reduce the creep experienced by purely physical gels and to increase the elastic modulus of purely chemical gels. Here, the physical-chemical gels were synthesized and characterized for their chemical, structural, thermal, mechanical and morphological properties. The gels were also tested for their gelation kinetics, swelling, degradation and cytotoxicity. The copolymers were successfully synthesized and their phase transition temperatures fall in a feasible range (29-34°C) for use in vivo. With rheology, it was shown that use of simultaneous physical and chemical gelation resulted in improved properties, with increased elastic moduli and reduced frequency dependence. The rates of reaction of thiols to vinyls differ between the two systems, demonstrating a greater effect of chemical gelation in one gelling system over the other, due to the faster rate of thiols consumed into reaction. The morphology of the gels proved to be quite different when analyzed by scanning electron microscopy, showing differences in swelling behaviors. Cell studies illustrated good growth of cells exposed to the gels. Both hydrogels, although possessing slight differences, demonstrate the capability of being injected in vivo for use as embolic agents for occlusion of aneurysms.