Temperature-Responsive Injectable Composite Hydrogels Based on Poly(N-Isopropylacrylamide), Chitosan, and Hemp-Derived Cellulose Nanocrystals

Injectable and temperature-responsive Poly(<i>N</i>-Isopropylacrylamide) (PNIPAAm)/Chitosan composite hydrogels reinforced with cellulose nanocrystals (CNCs) were successfully fabricated via photopolymerization. 0.1-3% (<i>w</i>/<i>v)</i> of cellulose nanocrystals were incorporated into the PNIPAAm/chitosan matrix to form thermo-responsive injectable composite hydrogels. FT-IR spectra confirmed the successful formation of these hydrogels, highlighting the characteristic peaks PNIPAAm, chitosan and CNCs. The inclusion of CNCs led to a reduced pore size as compared to the control hydrogels. The mechanical properties of the hydrogel were characterized under various temperature conditions. Rheology tests showed that storage modulus (G') increased significantly above 30 °C, indicating gel-like behavior. Thermogravimetric analysis showed thermal stability up to 300 °C. The volume phase transition temperatures (VPTT) of the hydrogels were found to be in the range of 34-38 °C, close to physiological body temperature. The equilibrium swelling ratio (ESR) of the CNC-containing hydrogels was higher than that of the control. In vitro studies with Human Dermal Fibroblast adult (HDFa) cells showed the hydrogels to be non-toxic, suggesting their potential for biomedical applications.