Nanocellulose reinforced P(AAm-co-AAc) hydrogels with improved mechanical properties and biocompatibility

Carboxylate modified cellulose nanofibril (CNF) was used to reinforce poly(acrylamide-co-acrylic acid) (P(AAm-co-AAc)) hydrogel via in-situ polymerization. With introduction of Fe3+-carboxylate complexation, a dual cross-linking network structure in the P(AAm-co-AAc)/CNF hydrogels was constructed, i.e. the covalently cross-linked acrylic components forming a macromolecular network, and the noncovalently COO--Fe3+ ionic coordination bonds acting as secondary cross-linking points. The microstructure of the hydrogels was characterized by scanning electron microscopy (SEM). By incorporating 0.6 wt% CNF, the elastic modulus, tensile strength and toughness of P(AAm-co-AAc) hydrogel were improved by 240%, 104% and 51%, respectively. The addition of CNF also enhanced the energy dissipation in loading and unloading tests. P(AAm-co-AAc)/CNF nanocomposite hydrogels showed water content (70-80%) comparable with that in human cartilage (75%). The biocompatibility tests suggested that P(AAm-co-AAc)/CNF had no toxicity to cells and cells can adhere and proliferate well on the surface, making it suitable for biomedical and tissue engineering applications.