Poly(N-isopropylacrylamide) and N-Isopropylacrylamide

N-Isopropylacrylamide is a biocompatible monomeric unit that can be used to form stimuli responsive polymers due to its temperature sensitive properties, including temperature-based volumetric and phase changes.

Since Pelton first synthesized temperature-sensitive Poly(N-isopropyl acrylamide) microgels in 1986, the responsive microgels have attracted considerable attention due to their potential applications, including controlled drug delivery, catalysis, and chemical separation.

Poly(N-isopropylacrylamide) is a synthetic thermogelling polymer that has received significant attention in tissue engineering and drug delivery. Aqueous solutions of poly(N-isopropylacrylamide) (PNIPAAm) exhibit a lower critical solution temperature (LCST), typically occurring around 32 - 34 °C. Below the LCST, water hydrates PNIPAAm chains. Above the transition temperature, the polymer becomes hydrophobic, resulting in a dramatic phase separation and formation of a solid gel without toxic monomers or crosslinkers. However, PNIPAAm homopolymers exhibit poor elastic properties and hold little water at physiological temperatures due to hydrophobicity.

Christiani et al. incorporate chondroitin sulfate covalently into the PNIPAAm network, which offers the potential for enzymatic degradability, anti-inflammatory activity, and increased water and nutrient absorption. PNIPAAm copolymers with CS were prepared by polymerizing the monomer NIPAAm in the presence of methacrylate-functionalized CS to form a grafted copolymer (PNIPAAm-g-CS). Because of the low crosslinking density of the copolymer, PNIPAAm-g-CS forms a viscous solution in water at RT and an elastic gel at physiological temperature due to the LCST. The polymer solutions become flowable again upon cooling below the LCST due to the reversibility of the transition.

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