Effect of clay content on electrostimulus deformation and volume recovery behavior of a clay-chitosan hybrid composite

Electrostimulus-responsive hybrid composites composed of chitosan (CS) and clay were successfully developed and systematically characterized. The addition of negatively charged clay as an ionic cross-linker strongly affect the cross-linking density as well as the mechanical property, swelling–deswelling behavior and fatigue property of the hybrids. With lower clay content, the crystallinity of the CS was slightly reduced, resulting in a decrease in the mechanical properties and an increase in the swelling ratio of the hybrid. However, the swelling kinetics were accelerated due to a reduction in CS crystallinity. On the other hand, with increasing clay concentration, the increased cross-linked bonding mechanically reinforced the hybrid beyond the aforementioned adverse effect, to show improved tensile strength and a decrease in the swelling ratio. The voltage-induced deformation of hybrids became more pronounced with increasing applied voltage, but became less pronounced with increasing clay content under an applied electric field. After repeatedly switching the electric field on and off, the higher clay concentration (C_clay > 0.5 wt.%) of the hybrid composites maintained the same capability of deswelling and swelling after more than 10 cycles, compared with both the pure CS film and the hybrid composites with lower clay content (e.g., 0.5 wt.%). Compared with pure CS, a significant improvement in the anti-fatigue property against cyclic electric stimulations of the hybrid was found, which encourages the use of such a new class of hybrid composite in medical and pharmaceutical applications.