Preparation And Properties Of Light-responsive Smart Hydrogels

Smart hydrogels are widely used in artificial muscles,biosensors,drug delivery control and biomedical micro-electromechanical devices due to their special functions such as super-stretching,stimulus response or self-healing.As one of smart hydrogels,light-responsive hydrogels have adjustable and intelligent effects mainly through the irradiation of light.There is no direct physical contact with external factors,which makes the light-responsive hydrogel cause great interest of researchers.In this paper,NIR light-responsive volume shrinkage hydrogels,NIR light-responsive self-healing hydrogels and UV cross-linking color changing smart hydrogels were studied.The structure,swelling properties and light-response characteristics of the hydrogels were characterized and analyzed The intelligent characteristics of the light-response were discussed,and the possible application fields were explored(1)Smart NIR light-responsive poly N-isopropylacrylamide(PNIPAM)nanocomposite hydrogels were prepared by incorporating sparse chemical cross-linking of small molecules The swelling properties,mechanical properties and NIR light-responsive properties of the pure PNIPAM,PNIPAM-graphene oxide(GO)and PNIPAM-GO-zirconia(ZrO2)hydrogels were invesitgated The introduction of GO induced PNIPAM the transformation from the thermosensitive to NIR light-responsive,and the oxidized groups of GO nanosheets could physically cross-link the PNIPAM chains to increase the toughness of the hydrogel networks ZrO2 powders could stabilize the hydrogel networks and strengthen the hydrogen bond interaction with the amide groups of PNIPAM chains,which greatly improved the loading capability and penetration resistance of PNIPAM-GO-ZrO2 composite hydrogel(2)Hydrophobically associating self-healing hydrogels,poly N,N-Dimethylacrylamide(PDMA),were prepared by copolymerization.The effects of GO doping content on the swelling properties,mechanical properties and self-repairing properties induced by NIR of PDMA-based hydrogels were studied Compared with the pure PDMA hydrogel,the equilibrium swelling ratio of the hydrogel decreased with the addition of lmg/mL GO.With the increase of GO content,the equilibrium swelling ratio of the hydrogel increased gradually due to the good hydrophilicity of GO nanosheets.When the concentration of GO was 5mg/mL,the mechanical properties of hydrogels were the best,because there were strong hydrogen bonds between GO nanosheets and the three-dimensional network of the hydrogel matrix,which improved the strength of the hydrogel.However,the presence of too many GO nanosheets hindered the copolymerization of SMA and DMAAm to a certain extent,and the reduction of chemical bond content reduced the strength of the hydrogel.After doping GO,the repair efficiency of hydrogel under the irradiation of NIR light was significantly improved.When the concentration of GO was more than 3mg/mL,the self-healing efficiency of hydrogels was close to 100%after NIR irradiation for 2h.As GO absorbed NIR light,the light energy was transformed into heat energy,which made the temperature of hydrogel rise obviously and was conducive to the movement of polymer chains.Under wet conditions,hydrophobic chains recombine and associate,and the damaged network structure of hydrogel was repaired to a certain extent.(3)PDMA-based discolored hydrogels were prepared by UV cross-linking.Because of the introduction of anthocyanins into hydrogels,the hydrogels exhibited pH-responsive discoloring properties.With the change of pH,the structure of anthocyanins could be transformed into each other,thus showing different colors.With the alternate repetition of pH=1 and 13,anthocyanins degraded and the color of hydrogels became lighter gradually.The hydrogel also had good self-healing property,and the combination of repaired hydrogel was strong.