Facile preparation of cellulose hydrogel with Achilles tendon-like super strength through aligning hierarchical fibrous structure

The extreme mechanical strength of fibrous connective tissues in the human body, such as ligaments and tendons, has always been challenging for hydrogel scientists. Here, we created extremely strong, purely cellulose-based hydrogels (DCC-E gels). The fracture stress and Young’s modulus of the gels were improved to the level of an Achilles tendon even at their equilibrium swollen state. To make DCC-E gels, regenerated cellulose gels were first prepared with ethanol as the anti-solvent. DCC-E gels were then prepared by applying Drying in Confined Condition method, where regenerated cellulose gels were prestretched and dried while their length was fixed. Although strength improvement of materials is typically only achieved at the expense of toughness, a significant increase in strength was achieved while maintaining high levels of toughness. The high strength and toughness of the DCC-E gels were realized by optimizing the cellulose fibril arrangement from nanoscale to macroscale, which was done by selection of an appropriate solvent used for cellulose regeneration. Parallel aggregated fibrous structures observed in the DCC-E gels are thought to play a central role in the enhancement of both toughness and strength. This study can assist in expanding the application of biopolymer-based hydrogels in tissue engineering and soft electronics.