Stimuli-response of gelatin hydrogel under direct current electric field

A gelatin hydrogel crosslinked with glutaraldehyde has been prepared, and its swelling ratio at equlibium, mechanical properties and stimuli-response behavior were studied. The results indicated that the water take-up of the gelatin hydrogel decreased as the concentration of NaCl solutions increased, and the mechanical properties of gelatin hydrogel films swollen in 0.01 mol/L NaCl solution are shown as follows:4.29 kPa of Young's modulus, 5.11 kPa of tensile strength and 110% of elongation at break. The hydrogel sheets bended toward the cathode under a non-contact D. C. electric field in NaCl aqueous solutions. The bending speed and deflection of the hydrogel sheets increased with increasing of the applied voltage. The electroresponsive behavior of the hydrogel was also affected by the electrolyte concentration of the external NaCl solution, and there is a critical ionic strength of 0.03. Under a cyclically varying electric field, the hydrogel sheets exhibited a good reversible bending behavior. The bending of gelatin hydrogels was initially explained by a bending theory of polyelectrolyte hydrogels based on the change of osmotic pressure due to the ion concentration difference between the inside and the outside of the hydrogel.