Doubly cross-linked nanocellulose hydrogels with excellent mechanical properties

Hydrogels are mostly used in biomedical sciences such as tissue engineering, drug delivery, and in vitro diagnostics. Nanocellulose hydrogels have multiple advantages because of their biodegradability, non-toxic properties, high water content and inherent biocompatibility. Moreover, 2,2,6,6-tetramethylpiperidinyl-1-oxyl(TEMPO)-oxidized cellulose nanofibrils (TOCNs) are completely individualized cellulose nanofibrils which have high aspect ratios, high elastic moduli, high strengths, high thermal stability, large surface areas, and large numbers of carboxylate groups on their surfaces. Here, the doubly cross-linked (DC) nanocellulose hydrogels with both ionic and chemical crosslinks were prepared and exhibited more improvement in mechanical properties than singly cross-linked nanocellulose hydrogels. The singly Fe³⁺ cross-linked nanocellulose hydrogel and chemically cross-linked nanocellulose hydrogel were broken at stresses of 117 kPa (strain = 80%) and 17 kPa (strain = 40%), respectively. The DC nanocellulose hydrogel exceeded a compressive strength of 450 kPa and a compressive strain of 90% without cracking. This greatly expands the application of nanocellulose hydrogels. Additionally, these nanocellulose hydrogels had good optical transparency and high swelling degree to meet the needs of practical applications. These DC nanocellulose hydrogels have great application prospects in the field of biomedical materials.