Hybrid CNCs/PNIPAAm Thermoresponsive Hydrogels Showing Enhanced Mechanical Strength and Biocompatibility

Thermoresponsive hydrogels contain an extraordinary quantity of water and possesstissue‐like properties, which makes them suitable for bio‐applications where reversible physical/chemical changes of the material are required. However, due to this high‐water content, the hydrogels often break upon phase‐changing, e.g., when switching to a swollen state under a thermal stimulus. A PNIPAAm hydrogel was incorporated with low percentages (< 1 wt%) of cellulose nanocrystals (CNCs) to enhance the mechanical properties of the hydrogel without affecting its thermoresponsiveness. The hybrid CNCs/hydrogels were synthesized using a simple in situ free radical polymerization procedure, in a simple and scalable mixing method. The hybrid hydrogels showed a 12% shrinkage from their original size when exposed to a temperature above the critical solution temperature of PNIPAAm. An improvement of the storage and loss modulus of 20× fold was observed for the CNCs‐hydrogel, compared to the PNIPAAm only. The hydrogels were applied as coatings on glass substrates without losing their thermoresponsive properties. Moreover, the hydrogels have no cytotoxic effects, with U‐2 OS cells showing over 99% viability following two‐day exposure to hydrogel extracts. These hybrid CNCs‐PNIPAAm hydrogels show high potential as biomaterials for tissue and cell engineering, wound dressings, medical adhesives, or drug delivery systems.