Rapid shape memory and pH-modulated spontaneous actuation of dopamine containing hydrogels

The dopamine containing hydrogels with rapid responsive shape memory capability were synthesized by a one-pot method. The temporary shape of hydrogel was fixed within 20 s in NaOH solution by the tris-complex crosslinking of metal-ligand complex between Fe 3+ ions and catechol groups, while the permanent shape was recovered completely in HCl solution within 60 s upon the change from tris-complex to mono-complex. The hydrogel showed unique spontaneous actuation behavior. It could curl spontaneously without further external force deformation when immersed in NaOH solution again after the first shape recovery in HCl solution. This might be attributed to the competitive result of swelling and additional tris-complex crosslinking formation when immersed in NaOH solution. In addition, the hydrogels also had proper modulus, elongation ratio and tensile strength. Such hydrogel provides a new candidate material for designing soft actuators and robots modulated with spontaneous actuating.