Editable and bidirectional shape memory chitin hydrogels based on physical/chemical crosslinking

Advances in soft robotics have enabled rapid progress in shape memory hydrogels, including unidirectional, bidirectional and multidirectional shape memory hydrogels. However, shape memory hydrogels with editable feature have hardly been reported. Here, chitin based bilayer hydrogels were prepared based on alkali/urea aqueous system. Due to the different swelling properties of the two layers, namely physical crosslinking layer and chemical crosslinking layer, the hydrogels can bend toward opposite direction in water and ethanol, showing a bidirectional shape memory behavior. Meanwhile, this bidirectional shape memory hydrogels can be programmed to different shapes with external force after immerging in alkali solution as a result of the hydrogen bond breakage and reformation via hydroxyl ion, displaying an editable feature. We believe that the editable and bidirectional shape memory chitin bilayer hydrogels have great potential in soft robotics.