Ionically conductive gelatin-based hybrid composite hydrogels with high mechanical strength, self-healing, and freezing-tolerant properties

Conductive hydrogels with stretchable three-dimensional (3D) polymeric networks are considered promising alternatives for electronic flexible devices. Fabrication of hydrogels with high mechanical strength, biocompatibility, and functionality remains challenging. In this study, we synthesized chitin nanowhiskers (ChNs) and dialdehyde microfibrillated cellulose (DAMFC) fibrils synergistically enhanced by gelatin hybrid composite hydrogels. The Schiff base reaction between the aldehyde groups on the surface of the DAMFC fibrils and the amino groups on the gelatin chains formed a large dynamic 3D network. DAMFC fibrils were covalently connected to the gelatin matrix, affording hydrogels high mechanical strength with a compressive stress of 3.482 MPa under 85% strain. In contrast, the dynamic Schiff base bonds endowed the hydrogels with good self-healing properties. The mechanical properties of the hydrogels were further improved by immersing the hybrid composite hydrogels in NaCl solution. The hydrogels exhibited good electrical conductivity and freezing tolerance. The investigated all-natural-polymer conductive hydrogels with high mechanical strength, freezing tolerance, and self-healing properties showed great potential in the fields of tissue engineering and flexible electronics.