thermia, and embolization, at the target location. [9,10] Recently, also soft-bodied wireless medical robots have become possible, where soft body enables programmable shape change, multifunctionality, and reconfiguration and safe operation inside the body. [11][12][13][14][15] Efforts have been made to develop and implement such robots, including fabrication of microscale soft robotic devices, and synthesis of biocompatible or biodegradable materials and strategies for locomotion inside the body. [16][17][18][19] However, applying these approaches have many limitations to operate safely and robustly in such complicated environments.Among various limitations, achieving strong adhesion to biological tissues whose surfaces are soft, rough, and wet is critical for the robots to efficiently implement various biomedical functions, including collecting bio-signals, bonding with unwanted derivatives and destroying them, healing wounds, and applying electrical impulses to nerves. [20][21][22][23] Although there are already commercial adhesives for tissues, the lack of long-term durability causes the failure of adhesion on the tissue. [24,25] Tough adhesives made of double-layered hydrogels [24][25][26] and dry double-sided tapes [27] were recently suggested for biological adhesives. These tissue adhesives are capable of strong adhesion to wet tissues, it is very difficult to detach them, indicating that a surgical operation is required for the detachment process. In addition, uncontrolled detachment can cause not only a problem of leaving an undesirable residue in Recently, the realization of minimally invasive medical interventions on targeted tissues using wireless small-scale medical robots has received an increasing attention. For effective implementation, such robots should have a strong adhesion capability to biological tissues and at the same time easy controlled detachment should be possible, which has been challenging. To address such issue, a small-scale soft robot with octopus-inspired hydrogel adhesive (OHA) is proposed. Hydrogels of different Young's moduli are adapted to achieve a biocompatible adhesive with strong wet adhesion by preventing the collapse of the octopus-inspired patterns during preloading. Introduction of poly(N-isopropylacrylamide) hydrogel for dome-like protuberance structure inside the sucker wall of polyethylene glycol diacrylate hydrogel provides a strong tissue attachment in underwater and at the same time enables easy detachment by temperature changes due to its temperature-dependent volume change property. It is finally demonstrated that the small-scale soft OHA robot can efficiently implement biomedical functions owing to strong adhesion and controllable detachment on biological tissues while operating inside the body. Such robots with repeatable tissue attachment and detachment possibility pave the way for future wireless soft miniature robots with minimally invasive medical interventions.
