A thermo and photoresponsive dual performing hydrogel for multiple controlled release mechanisms

Abstract

A hydrogel with dual thermo and photoresponsive characteristics was developed. Using poly(N-isopropylacrylamide) (PNIPAM) as the thermosensitive unit, the hydrogel network can undergo reversible swelling/shrinking behavior under different temperatures (20 °C and 37 °C) stimulation. A supramolecular host–guest complex composed of azobenzene (Azo) and α-cyclodextrin (α-CD) was used as the photosensitive unit. Azo and α-CD can undergo reversible recombination/dissociation behavior under the stimulation of different wavelengths of light (365 nm and 430 nm). Methylene blue (MB) was selected as the model drug to measure the controlled release behavior of the hydrogel under different temperatures and photoirradiations. The experimental results showed that the hydrogel containing the thermosensitive component (PNIPAM) and the photosensitive component (α-CD/Azo) released 69.3% and 47.2% of MB at 20 °C and 37 °C, respectively. Under the condition of light wavelengths at 430 nm and 365 nm, 73.2% and 65.6% of MB were released, respectively. The results showed that α-CD and Azo formed a supramolecular host–guest complex, which could undergo reversible binding/dissociation under the action of light stimulation, thereby controlling MB to enter and exit CD cavity. In addition, when the ambient temperature was lower or higher than the lower critical solution temperature of PNIPAM (LCST, 32 °C), the hydrogel underwent a responsive volume change to control the loading and release of MB molecules. So, combining the dual thermo and photoresponsibility, this smart hydrogel could be applied for multiple controlled release mechanisms.