| Hydrogels,which consist of a water-swollen three-dimensional polymer network,can absorb a large amount of water and maintain the original structure without being dissolved.Due to its properties of high moisture content,rapid swelling,soft,rubbery viscous and good biocompatibility,hydrogels have a wide range of applications in tissue engineering,drug delivery systems,and medical devices;Microgels are nanometer-and micrometer-sized of the threedimensional network of polymer particles by solvent swelling,whose particle size can be regulated by external stimuli.The Supramolecular interactions are applied to the gel system,which can achieve reversible control of the gel properties due to the reversible and dynamic,giving the materials a new function.In this paper,we focused on the design of photo-responsive supramolecular crosslinkers based on the host-guest interaction between cyclodextrin(CD)and photoisomerizable azobenzene(Azo),which was used to construct the structure of gels.The lightcontrolled self-healing and degradation of the materials were examined at different microscopic levels.The results of specific research are as follows:1.Firstly,Water-soluble poly-(?-CD)nanogels were obtained by cross-linking ?-cyclodextrin(?-CD)monomer with epichlorohydrin under basic conditions.Then the host–guest macrocrosslinker was assembled from poly-(?-CD)nanogels and azobenzeneacrylamide,which was used to crosslink acrylamide monomer to obtain novel hydrogel with light-tunable self-healing properties.After the damage of the hydrogel material,the hydrogel could repair its wound autonomously through the dynamic host–guest interaction between trans-Azo and ?-CD.In addition,the wounded hydrogel will lose its ability of self-healing when exposed to ultraviolet light(UV)due to the transition from trans-Azo to cis-Azo,and the self-healing behavior could be recovered upon the irradiation of visible light when the cis-Azo became trans-Azo.2.A dynamic supramolecular crosslink(?-CDAAm @ AzoAAm)with one acrylamide on each end on the basis of noncovalent host-guest interactions between(Azo)and ?-cyclodextrin(?-CD)which was used in the precipitation polymerization of N-isopropylacryamide(NIPAM)to synthesize microgels containing light-responsive crosslinkers.The photoisomerizable azobenzene moiety can change its binding affinity with ?-CD causing the variety of crosslinking density.The microgels can deswell upon UV irradiation(? = 365 nm)due to the decomplexation of host-guest system with the dissolving of polymer chains.And the polymer chains can reassemble when irradiated with visible light(? = 450 nm)due to the complexation of host-guest system with the reconstruction of crosslinks,as the cis-Azo are converted to trans-Azo state.Interestingly,heating can benefit the reassemble in a certain degree due to the thermally driven.3.A series of core-shell structure supramolecular microgels were successfully prepared by controlling the adding order and the amount of(NIPAM)monomer,supramolecular crosslinker(?-CDAAm @ AzoAAm)and N-N methylene bisacrylamide(BIS)crosslinker with the free radical precipitation polymerization.The supramolecular crosslinker(?-CDAAm @ AzoAAm)can remotely control the particle size of in different networks of microgels.These results indicate that the introduction of photo-responsive supramolecular crosslinkers into gel system can be successfully designed to construct the network structure of gels,giving the gel a new stimuli-responsive mode of light.So the supramolecular crosslinkers can intelligently regulate the properties of gels on the macroscopic and microscopic levels remotely and reversibly.It has a good application prospect in the fields of designing light-controlled smart materials,optical storage and biological materials. |
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