Photoinduced Iron Reduction Achieves Shape Memory And Solvent-actuated Behavior Of Hydrogels

Hydrogel represents a class of soft and flexible material composed of hydrophilic polymer network and a large amount of water molecules permeated within.Hydrogels are biocompatible and mechanically similar to human tissues,makin them quite promising in a wide range of application fileds.Shape memory hydrogels possess the ability to change their shape by a programming process and later recover to the original shape by a proper stimulus.So far stimuli like heat,light,electricity and ultrasound have been developed to realize shape recovery of shape memory hydrogels.Among them,light is advantageous in its remote and spatiotemporal controllability.However,the preparation of light-responsive hydrogels usually requires sophisticated design and synthesis,which is the main limitation for the development of light-responsive shape memory hydrogels.In this thesis,we introduce the photo-reduction of Fe³⁺-carboxylate coordination process to the design of hydrogels as a molecular switch,which can be oxidized to form again by oxygen in air.After a systematic optimization,the hydrogels exhibit excellent shape memory properties and reversible actuating functions upon solvent exchange.The main points are summarized as follows.A new design of hydrogel,leads Fe³⁺-COOH into hydrogel as molecular switch of shale memory process,and prepares photoresponse shape memory hydrogel with good mechanical property,strong deformation capacity,high fixed rate and recovery through a convenient approach,while researches its potential applications,which mainly contain following contents.1.Systematically study shows that the hydrogel has excellent shape memory properties,up to 680%tensile strain can be fixed,and the shape fixity ratios can be higher than 90%and the shape recovery ratios is approaching 100%.2.Hydrogels fixed with tensile strain exhibit reversible bending behaviors upon UV irradiation,which is due to gradient dissociation of Fe³⁺-carboxylate coordination along the thickness direction.3.The hydrogel after irradiation bearing different regions with drastically different modulus and crosslinking density,which leads the hydrogel exhibiting altered swelling and shrinking rates and extents in different solvents,such as water and ethanol.4.Based on the same principle,photo-induced surface patterning can be applied to realize reversible deformation of micro-patterns on hydrogel surface.Moreover,the deformation can be anisotropically controlled by the orientation extent and degree of the hydrogel matrix.