Preparation And Release Property Study Of Dually Thermoand Photo-responsive Hydrogel Containing ?-CD Moiety

Hydrogel is a polymer material with a three-dimensional network structure.Due to the presence of hydrophilic groups and cross-linked structures,it has the characteristics of swelling with water and keeping the original structure from dissolving.The introduction of smart hydrogels formed by different sensitive components through graft polymerization can respond to external environmental stimuli such as light,temperature,pH,etc.Different types of stimulus response systems have their own characteristics and advantages.Among them,the temperature-sensitive hydrogel can effectively load and release drug molecules through the volume responsive change of swelling/shrinking under different temperature stimuli,so it has been deeply researched and developed in the field of drug controlled release.In recent years,light-sensitive hydrogels formed by introducing cyclodextrin and azobenzene(Azo),a light-controlled supramolecular system with host-guest recognition,into hydrogels because of their safety and the unique advantages such as convenience have gradually attracted more and more attention from researchers.The purpose of this research is to prepare a thermo-and photo-responsive hydrogel containing ?-cyclodextrin(?-CD)and study its controlled release properties.The thermo-sensitive component is poly-N-isopropylacrylamide(PNIPAM),and its polymer network undergoes reversible swelling/shrinking volume changes above and below the lowest critical phase transition temperature(LCST),which enables it to treat drug molecules in the environment.Effective adsorption and release.The photosensitive component is a photo-controlled supramolecular system composed of ?-CD and Azo with host-guest recognition.The cyclodextrin cavity increases the loading site of drug molecules while using the selective inclusion effect of ?-CD on cis/trans Azo,using ultraviolet light(365nm)and visible light(430nm)as the illumination light source.By achieving reversible combination/dissociation changes between the two,the "switch" of the ?-CD cavity is controlled to achieve the purpose of controlling the free/fixed state transition of drug molecules in the ?-CD cavity.The smart hydrogel prepared by combining the dual advantages of thermo-sensitive and photo-sensitive responsemechanisms,through the responsive coordination between the two sensitive systems,on the basis of increasing the drug load,realize the real-time regulation of the release mode of drug molecules.In this paper,the modified photo-sensitive component and thermo-sensitive component are introduced into the polymer network by graft polymerization.A photothermal dual-stimulus response hydrogel containing ?-CD(PNIPAM-Azo/?-CD).The infrared spectroscopy(FTIR),nuclear magnetic resonance(NMR),elemental analysis(EA)and integrated thermal analysis(TG-DSC)and other test methods were used to analyze and characterize the intermediates and hydrogels.At the same time,the reversible photo-isomerization effect and photo-isomerization rate of the Azo group in the photosensitive component of the hydrogel were tested,and the swelling/de-swelling effect of the temperature-sensitive component could be detected.The effects of the content ratio of crosslinking agent and N-isopropylacrylamide on the swelling/de-swelling properties of hydrogels were also studied.The results show that the photosensitive component and the thermo-sensitive component grafted into the hydrogel have good photostimulation response and temperature stimulus response,respectively,and can achieve the photoisomerization change of the Azo group by light stimulation and temperature stimulation.Responsive behavior of swelling/shrinking of hydrogel polymer networks.Finally,using methylene blue(MB)as the model drug model,the drug loading and release behavior of the hydrogel under different temperatures(20/37?)and different wavelengths of light(365/430nm)was investigated.The results show that the recombination/dissociation behavior of the Azo group and ?-CD in the hydrogel polymer network under light stimulation can regulate the loading and release of MB molecules.When the ambient temperature is higher than LCST,PNIPAM-Azo/?-CD undergoes rapid volume shrinkage,which realizes the pulsed release of MB molecules.Then,as the polymer network continues to collapse,the mesh shrinks,and a dense layer is formed on the surface,which ultimately hinders The release of MB molecules.When the ambient temperature is lower than LCST,the polymer network absorbs water and expands,which is beneficial to the free release of MB molecules.The comprehensive results indicate thatthe PNIPAM-Azo/?-CD in combination with the light stimulation response and temperature stimulation response system.After the photosensitive component and the temperature-sensitive component are grafted into the hydrogel,they can realize the selective recognition effect of ?-CD on the Azo group and MB molecule by light stimulation,and the swelling of the hydrogel polymer network by temperature stimulation /Shrinking response behavior.Comprehensively shows good drug storage and controlled release performance.Finally,the Ritger-Peppas equation was used to study the release mechanism of the hydrogel.The results showed that the dominant release mechanism of MB was the non-Fickian diffusion mechanism.