Moreover, the chemical reactions used for detachment are often slow and not fully reversible. Despite the great success of these methods, using additional triggers still makes detachment inconvenient. Zhao and co-workers introduced a disulfide bond into covalent linkages to render redox-controlled reversible detachment and attachment 37. For example, Suo and co-workers implemented a photolysable bond to allow detachment of adhesives upon UV light illumination 36. To meet these needs, a few strategies have been introduced. It remains challenging to develop bio-adhesives that can rapidly, robustly, and conformally integrate with various wet tissues or bioelectronic devices yet detachable if misplaced 35. In particular, as most surgeries are operated on dynamic tissue surfaces, mispositioning tape-type adhesives is almost unavoidable. However, once covalent adhesion bonds are formed, the adhesives cannot be removed easily 32, 33, 34. These adhesives are mechanically robust and can function properly on dynamic surfaces or tissues bearing considerable tension. To circumvent these drawbacks, tape-type adhesives based on covalent surface bonding have been introduced 29, 30, 31. They are also prone to detach from surfaces due to swelling of the adhesives or bleeding from the tissue 24, 25, 26, 27, 28. Tape-type adhesives can be instant and reversible, but the adhesion strength is typically low (<50 kPa) if they only form non-covalent bonds with the tissues. This long curing time greatly limits their applications in scenarios that require rapid and strong adhesion, such as attaching bioelectric devices to a beating heart or instant hemostasis 17, 18. Glue-type adhesives require a long curing process (hours to days) to establish strong cohesion and interfacial adhesion. Recently, bio-adhesives have emerged as potential alternatives to sutures 3, 4, 5, 6, as they are biocompatible, nontoxic, and easy to use 7, 8. However, suturing may cause tissue damage or scars at the fixing points and is difficult to apply to tissues with complex structures (e.g., spinal cord and heart). Sutures have long been the first choice in surgery for hemostasis, wound closure, and integration of bioelectronic devices 1, 2. Given that the hydrogel tapes are biocompatible, easy to use, and robust for bio-adhesion, we anticipate that they may find broad biomedical and clinical applications. We demonstrate that the tapes show fast and reversible adhesion at the initial stage and ultrastrong adhesion after the formation of covalent linkages over hours for various tissues and electronic devices. Specifically, inspired by the catechol chemistry discovered in mussel foot proteins, we develop an electrical oxidation approach to controllably oxidize catechol to catecholquinone, which reacts slowly with amino groups on the tissue surface. This timescale-dependent adhesion mechanism allows instant and robust wet adhesion to be combined with fault-tolerant convenient surgical operations. Here, we report hydrogel tapes that can form strong physical interactions with tissues in seconds and gradually form covalent bonds in hours.
Repositioning misplaced adhesives during surgical operations may cause severe secondary damage to tissues.
However, most strong bio-adhesives rely on the instant formation of irreversible covalent crosslinks to provide strong surface binding. Fast and strong bio-adhesives are in high demand for many biomedical applications, including closing wounds in surgeries, fixing implantable devices, and haemostasis.