Selectively Detachable Hydrogel Adhesion Enabled by Stimulus-Specific Cleavable Cross-Linkers

The development of detachable hydrogel adhesion presents an advancement in the fields of soft electronics and bioengineering as it offers additional functionalities to these applications. However, conventional methods typically rely on a single detachment trigger, so it is unclear whether unintentional detachment might occur in the specific environments of other detachment systems. This makes it difficult to directly introduce two independent detachment triggers directly. In this article, we present a strategy for selective detachable adhesion based on two types of cleavable cross-linkers, <i>N</i>,<i>N</i>'-bis(acryloyl)cystamine (BAC) and <i>N</i>,<i>N</i>'-(1,2-dihydroxyethylene)bis(acrylamide) (DHEBA), each with an independent cleavage trigger. BAC can be cleaved through the reduction of disulfide bonds using reducing agents, while DHEBA can be hydrolyzed through heating. We constructed stitching polymer networks for topological adhesion using two types of cleavable cross-linkers, allowing the networks to be selectively degraded depending on which cross-linker was used. Our findings show that the use of cleavable cross-linkers achieved selectively detachable adhesion in various hydrogels, with adhesion energy that reached up to 1223 J m^-² in polyacrylamide-alginate (PAAm-alginate) tough hydrogel. This strategy also proved versatile as it led to effective adhesion with various substrates, including aluminum, copper, glass, and polyester film (PET). Furthermore, we took advantage of the high programmability of this approach to construct hydrogel-based YES and AND logic gates, whose output changed depending on the applied input triggers. In addition, we designed a selective-release capsule model capable of dual-solution release, which emphasizes the potential of our strategy in creating programmable and responsive soft materials.