covalent bonds is typically hard to remove. Adhesion through physical interactions may be detachable, but usually requires solvents to act at the bonding front [25,30] ; the operation can be time-consuming and environmentally harmful. Some traditional adhesives are chemically modified to be detachable upon a change in temperature (e.g., epoxy) [31,32] or an exposure of light (e.g., pressure-sensitive adhesive), [23,33] but they are usually cytotoxic and ineffective for wet materials like hydrogels and living tissues. Some bioinspired adhesion systems also use noncontact stimuli like temperature or magnetic field to trigger detachment. [34][35][36] Nevertheless, their adhesions rely on specific materials with special surface geometry, or generate low adhesion energy (1-10 J m −2 ). Achieving both strong adhesion and easy detachment has been a challenge.Here we describe an approach to achieve both strong adhesion and lighttriggered easy detachment. We first describe the principle of strong and photodetachable adhesion using two hydrogels as adherends (Figure 1). Each hydrogel aggregates water molecules and a covalent polymer network. The polymer networks in the two hydrogels have no matching functional groups for bonding, so that the two hydrogels by themselves adhere poorly. We achieve strong adhesion by spreading an aqueous solution of polymer chains on the surfaces of the two hydrogels, and triggering the polymer chains to cross-link into a third polymer network in situ, in topological entanglement with the preexisting polymer networks of the two hydrogels. The third polymer network acts as a molecular suture that stitches the two preexisting polymer networks of the hydrogels together. This process is called topological adhesion, or topohesion for short. [25] We achieve photodetach by functionalizing the stitching polymer network for photodetach, and triggering the network to dissociate upon an exposure to light of a certain frequency range.The principle described above requires two triggers. The first trigger, which we call the topohesion-trigger, causes the stitching polymer chains to cross-link into a new polymer network in topological entanglement with the preexisting polymer networks of the two hydrogels. The second trigger, which we call the photodetach-trigger, causes the stitching network to dissociate in response to light of certain frequency range. Conceivably the two triggers can be realized with various chemistries. Here we demonstrate topohesion and photodetach using two facts of chemistry: 1) Fe 3+ ions and carboxyl groups form coordination complexes, [37,38] and 2) the coordination complexes

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Bioelectronic implantable systems (BIS) targeting biomedical and clinical research should combine long‐term performance and biointegration in vivo. Here, recent advances in novel encapsulations to protect flexible versions of such systems from the surrounding biological environment are reviewed, focusing on material strategies and synthesis techniques. Considerable effort is put on thin‐film encapsulation (TFE), and specifically organic–inorganic multilayer architectures as a flexible and conformal alternative to conventional rigid cans. TFE is in direct contact with the biological medium and thus must exhibit not only biocompatibility, inertness, and hermeticity but also mechanical robustness, conformability, and compatibility with the manufacturing of microfabricated devices. Quantitative characterization methods of the barrier and mechanical performance of the TFE are reviewed with a particular emphasis on water‐vapor transmission rate through electrical, optical, or electrochemical principles. The integrability and functionalization of TFE into functional bioelectronic interfaces are also discussed. TFE represents a must‐have component for the next‐generation bioelectronic implants with diagnostic or therapeutic functions in human healthcare and precision medicine.

Flexible and soft bioelectronics display conflicting demands on miniaturization, compliance, and reliability. Here, the authors investigate the design and performance of thin encapsulation multilayers against hermeticity and mechanical integrity. Partially cracked organic/inorganic multilayer coatings are demonstrated to display surprisingly year‐long hermetic lifetime under demanding mechanical and environmental loading. The thin hermetic encapsulation is grown in a single process chamber as a continuous multilayer with dyads of atomic layer deposited (ALD) Al2O3‐TiO2 and chemical vapor deposited Parylene C films with strong interlayer adhesion. Upon tensile loading, tortuous diffusion pathways defined along channel cracks in the ALD oxide films and through tough Parylene films efficiently postpone the hermeticity failure of the partially cracked coating. The authors assessed the coating performance against prolonged exposure to biomimetic physiological conditions using coated magnesium films, platinum interdigitated electrodes, and optoelectronic devices prepared on stretchable substrates. Designed extension of the lifetime preventing direct failures reduces from over 5 years yet tolerates the lifetime of 3 years even with the presence of critical damage, while others will directly fail less than two months at 37 °C. This strategy should accelerate progress on thin hermetic packaging for miniaturized and compliant implantable electronics.