Highly Efficient Switchable Underwater Adhesion in Channeled Hydrogel Networks

The ability to switch adhesion strength is a highly desirable property for adhesives applied in a wet environment. The major challenges involve the presence of a water layer between the substrate and adhesive, and the incorporation of efficient switching mechanisms. Despite the recent progresses in devising such systems, there exist several intrinsic limitations in the current strategies, such as high residual adhesion, the use of solid–liquid transition, or thin film configurations. Herein, a channeled poly(N-isopropylacrylamide) (PNIPAm) hydrogel containing bio-inspired dopamine-comonomers is reported, which undergoes temperature-controlled reversible switching of underwater adhesion on both hydrophilic and hydrophobic surfaces. The introduction of microscopic channels inside the hydrogel, achieved by removing a sacrificial agarose network, greatly facilitates water removal from the interface and thus promotes underwater adhesive strength. On glass, the maximum adhesive stress of the channeled hydrogel can reach six times that of hydrogels without channels. Additionally, high switching efficiency and low residual adhesion can be achieved by the thermal phase transition of the PNIPAm network, also demonstrated by the capture and release of lightweight, irregular, fragile, and biological objects using the hydrogel. The channeling strategy provides implications for designing future underwater adhesive systems for, e.g., soft robotics or biomedical applications.