Dual-responsive composite hydrogels based on TEMPO-oxidized cellulose nanofibril and poly(N-isopropylacrylamide) for model drug release

Dual responsive composite hydrogels were successfully prepared by combining cellulose nanofibril (CNF) isolated by 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidation with thermally responsive poly(N-isopropylacrylamide) (PNIPAAm) for drug release at 10 wt% CNF loading and - 20 degrees C polymerization temperature. pH responsive hydrogels were acquired by adjusting the carboxyl charge level of the CNF during TEMPO-mediated oxidation. CNF-PNIPAAm hydrogels fabricated were characterized in regards to compressive strength, functional group, low critical solution temperature (LCST), and swelling ratio of the hydrogels at different temperatures from 20 to 60 degrees C and pH levels from 2 to 10. Finally, the drug release behavior of these hydrogels was also investigated using methylene blue as a model drug. As the carboxylate content increases, the dual responsiveness of hydrogel improved at the expense of the compression strength. The CNF-PNIPAAm hydrogels were swollen and translucent below the LCST, and shrunken and opaque above the LCST. The Higuchi and the Krosmeyer and Peppas model was best-fitted to the drug release behavior of these hydrogels at pH 10 and pH 2, respectively. The results also indicated that a proper selection of polymerization temperature provided a way of tuning the dual-responsiveness of the hydrogels. These results also suggest that the CNF-PNIPAAm hydrogels can release drugs on demand.