A Reversible Underwater Adhesion Hydrogel Based On Shape-memory Effect

Hydrogel have attracted much attention because of their excellent biocompatibility and high water content,with many encouraging applications such as wound dressings,medical adhesives,wearable devices.These applications all rely on the adhesion of hydrogel.The adhesion of hydrogel to a large extent determines the scope of application.However,the adhesion of traditional adhesive hydrogel will be significantly weakened in wet environment,and the adhesion is difficult to control.Inspired by the wet adhesion microstructure of treefrog foot-pads,a new reversible underwater adhesion strategy is proposed in this study.We synthesize an anti-swelling hydrogel with shape-memory property.We achieve excellent drainage effect and enhance the adhesion performance of the hydrogel in wet environment by constructing a microstructure on the surface of the hydrogel.Reversible underwater adhesion property depends on the shape-memory property of hydrogel.After heating,the surface microstructure of the hydrogel recovers and the flat structure is formed again,which reduces the adhesion of the hydrogel and makes it easy to detach.The water retention property of hydrogel are further enhanced by introducing moisturizing components into the hydrogel.Firstly,the long-chain chemical crosslinker PEG-DMA and physical crosslinker UM are synthesized.Organogel is synthesized by free radical copolymerization and hydrogel is formed by solvent exchange.Two physical interaction forces,hydrogen bond and dipoledipole interaction,are introduced into hydrogel to obtain shape-memory and excellent antiswelling properties.Furthermore,the composition proportion of hydrogel is further optimized to improve the performance of hydrogel,and the related properties of hydrogel are characterized.Meanwhile,the mechanism of anti-swelling and shape-memory property is studied.Secondly,hydrogel have excellent underwater adhesion property by constructing microstructures on the surface of hydrogel.The change of microstructure depends on the shape-memory property of the hydrogel.The microstructure of the surface of the hydrogel is restored to the flat structure through thermal stimulation,and the adhesion property of the material is reduced,so as to achieve the purpose of controlling the adhesion property of the hydrogel through temperature.The experimental results show that the hexagonal microstructure plays a key role in determining the wet adhesion property of hydrogel.The mechanism of the microstructure in wet adhesion and the mechanism of the reduction of adhesion after shape-memory recovery are also studied.Finally,the water retention property of hydrogel is further enhanced by introducing moisturizing components into the hydrogel.Hydrogel can maintain excellent performance even after long term use by virtue of glycerol’s excellent water retention.The effect of glycerol with different volume fraction on the water retention property of hydrogel is studied.The influence of the moisturizing components on the original properties is characterized and the biocompatibility of the hydrogel is characterized by in vitro cell experiment.