Stimulus-responsive Shape Memory Hydrogels And The Investigation Of Spontaneous Actuation

Super strong hydrogels with shape memory behavior and spontaneous actuation hydrogels were prepared.Firstly,super strong hydrogels with hydrophobic association were obtained by solvent exchange.The dynamic reversible hydrophobic association endowed the gels with solvent responsive shape memory and actuation properties.Secondly,the catechol group was introduced in the hydrogel to prepare pH-triggered shape memory hydrogels with spontaneous actuation behavior.Finally,the principle of universality of spontaneous actuation of the hydrogels induced by swelling was investigated.The main contents and results are as follows:1.Solvent responsive gels were synthesized by copolymerization of the hydrophobic monomer butyl methacrylate?BMA?and hydropholic monomer methacrylic acid?MMA?and an N,N?-methylenebisacrylamide?BIS?crosslinker in a mixed solvent of H₂O and DMSO.Immersion the as-prepared gel in H₂O for specific time induced the super strong hydrogel with tensile strength up to 9 MPa and moduli to 200 MPa,which are comparable to the strength of human cartilage and skin.The reversible change of crosslinked network triggered by reversible formation and dissociation of the hydrophobic association in H₂O and DMSO endowed the BMA gels with excellent shape memory,reversible volume change and other interesting properties.Solvent responsive ultra-fast actuating and recovering of the rubber-gel bilayer composite soft actuator were achieved within 30 s.2.The dopamine containing hydrogels with rapid responsive shape memory capability were synthesized with one-pot method by copolymerizing the dopamine methacrylamide?DMA?,N,N-dimethylacrylamide?DMAA?and BIS.The temporary shape of the hydrogel was fixed within 20 s in NaOH solution by the tris-complex crosslinking of metal-ligand complex between Fe³⁺ions and catechol groups,while the permanent shape was recovered completely in HCl solution within 60 s upon the change from the tris-complex to the mono-complex.This hydrogel showed unique spontaneous actuation behavior,the hydrogel with little residual spiral shape can curl spontaneously without further external force deformation when immersed in NaOH again.This might be attributed to the competitive result of swelling and additional tris-complex crosslinking formation when immersed in NaOH solution.3.Further systematic investigation on the spontaneous actuation of different kinds of hydrogels found fast asymmetry swelling was the main factor to trigger the spontaneous actuation.The PAA hydrogels could fix the spiral shape in NaOH with external force.This was the results of asymmetrical swelling at the beginning of swelling caused by diffusion effect.The edges swelled before the inside of the hydrogels thus the volume between the edges and inside was different and then the spiral shape was fixed.The PAA hydrogels could recover to original shape in HCl solution due to deswelling which decreased the difference of volume between the edges and inside.The hydrogels with little residual spiral shape could spontaneously actuate between spiral shape and original shape by alternately immersing the gel in NaOH and HCl solution,because the asymmetrical swelling and deswelling forced the gel to curl and the hand of curl was induced by the residual spiral shape.This phenomenon only happens at the beginning of the hydrogels with fast swelling and deswelling.The spiral shape disappeared when the gels were equilibrium swelling and the hydrogels couldn't spontaneously actuate at the same time.