An Integrally Formed Janus Hydrogel for Robust Wet-Tissue Adhesive and Anti-Postoperative Adhesion.

Facile fabrication of asymmetrically adhesive hydrogel with robust wet tissue adhesion simultaneously with effective anti-postoperative adhesion still remains a great challenge. In this work, an integrally formed Janus hydrogel is facilely fabricated in one step by controlling the interfacial distribution of free carboxyl groups on the two sides of hydrogels. At a lower stirring speed, the generated bigger sized emulsion droplets mainly occupy the top surface of hydrogel, which effectively hinders the exposition of carboxyl groups on the top surface, driving them to be more distributed on the bottom surface, ultimately resulting in the poor adhesion of top surface but robust adhesion of bottom surface to various wet tissue even underwater. The difference in adhesive strength achieves as high as 20 times between the two surfaces. In vivo rabbit experiment outcomes clearly validate that the bottom surface of hydrogel firmly adheres to the stomach defect, and the other opposite surface can efficiently address the postoperative adhesion problem. Besides, this hydrogel exhibits superior mechanical toughness and conductivity which has been used as a highly adhesive strain sensor to real-time monitor the beating heart in vivo. This simple yet effective strategy provides a much more feasible approach for creating Janus hydrogels bioadhesives.