Preparation of PNIPAM Hydrogel Containing Lipoic Acid

Poly(N-isopropylacrylamide) (PNIPAM) hydrogel has been studied as an important drug delivery system due to its volume transition or temperature-responsive swelling properties, whose phase separation temperature is similar to the body temperature. However, because of hydrophilic PNIPAM, hydrophobic drugs are difficult to be uniformly loaded in the networks. Antioxidant alpha-lipoic acid (LA) can be prepared as a polymer(polylipoic acid, PLA) by ring opening polymerization, which is hardly developed as a material due to its low molecular weight and easy depolymerization. To overcome this limitation, a hydrophobic active ingredient, LA was reacted with NIPAM into stable hydrogels. Simple thermal radical reaction successfully resulted in a hydrogel (PNIPAM/PLA), which was confirmed by DSC, FTIR, and Raman spectroscopy. The PNIPAM/PLA showed temperature-responsive properties, and their volume swelling decreased with an increase in lipoic acid content. These hydrogels can carry hydrophobic drugs with PNIPAM and the hydrogels could be useful as final drug delivery systems having lipoic acid as an antioxidant.