Adhesion strategies that rely on mechanical interlocking or molecular attractions between surfaces can suffer when coming into contact with liquids. Thus far, artificial wet and dry adhesives have included hierarchical mushroom-shaped or porous structures that allow suction or capillarity, supramolecular structures comprising nanoparticles, and chemistry-based attractants that use various protein polyelectrolytes. However, it is challenging to develop adhesives that are simple to make and also perform well-and repeatedly-under both wet and dry conditions, while avoiding non-chemical contamination on the adhered surfaces. Here we present an artificial, biologically inspired, reversible wet/dry adhesion system that is based on the dome-like protuberances found in the suction cups of octopi. To mimic the architecture of these protuberances, we use a simple, solution-based, air-trap technique that involves fabricating a patterned structure as a polymeric master, and using it to produce a reversed architecture, without any sophisticated chemical syntheses or surface modifications. The micrometre-scale domes in our artificial adhesive enhance the suction stress. This octopus-inspired system exhibits strong, reversible, highly repeatable adhesion to silicon wafers, glass, and rough skin surfaces under various conditions (dry, moist, under water and under oil). To demonstrate a potential application, we also used our adhesive to transport a large silicon wafer in air and under water without any resulting surface contamination.

on dry and rough surfaces (maximum ≈10 N cm −2 ). [1] Close observations have indicated nanoscale hairs of high aspect ratio (AR) with slated tips. [21][22][23][24][25][26][27][28][29][30] This geometry allows directional appliance of van der Waals forces against engaged surfaces for stable attachment. The attachment strategies and fixation systems of beetles have also been investigated. [9] Concave, mushroom-shaped architectures on the forelegs of beetles ensure stable adherences onto rough, waxy surfaces [31][32][33][34][35][36] or locomotion via capillary adhesion. [37][38][39] Studies on their attachment systems revealed that the mushroom-shaped structures with wide concave tips can generate van der Waals interactions [40] as well as a suction effect against engaged surfaces. [41,42] Moreover, needles located in the proboscis of mosquitos [43][44][45][46] or endoparasites (e.g., Pomphorhynchus laevis) [47] alike, induce mechanical interlocking on dry skin or wet organs. The needles provide strong adhesion in both normal and shear directions for the insect species to easily consume nutrients. Recently, the architectures of octopus suckers were investigated to understand their underlying attachment mechanism. Existing in clusters on octopus tentacles, suction cups are crucial for octopi's survival underwater for functions such as preying, grasping, locomotion, and even sensing. The cup-shaped protruding chamber (infundibulum) is known to adapt and seal conformably on rough surfaces. [12,13,15,48] Meanwhile, the dome-like protuberance in the lower chamber (acetabulum) forms pressure difference between the segregated lower and upper chambers within the suction cup architecture. [49] This enhances suction stress to adhere strongly onto wet or underwater surfaces. The footpads of slugs are covered with structures of microscale compression waves with viscous mucus. This can be used to both lubricate a slug's movement over surfaces and facilitate the transfer of adhesive force to the engaged surfaces. [16,19,20,[50][51][52] Specifically, the mucus with interpenetrating positively charged chemistries produce pedal waves; this in all creates an adhesive and elastic dissipative matrix, and guides the movement of slugs on attached surfaces. [53] Hence, structural features within the as-mentioned organisms have built the platform of bioinspired adhesive systems for potential use in clean transfer systems, [54][55][56][57][58][59] soft robotics, [60,61] stimuli-responsive adhesives for dry or wet surfaces, [62][63][64] and various wearable devices with diagnostic and therapeutic functionalities. [65][66][67][68][69] Among various applications of bioinspired multiscale architectures, patches attachable to skin have been of high interest (Figure 1b). Human skin, the outermost organ of the human The attachment phenomena of various hierarchical architectures found in nature have extensively drawn attention for developing highly biocompatible adhesive on skin or wet inner organs without any chemical glue. Structural adhesive sy...

Amphibian adhesion systems can enhance adhesion forces on wet or rough surfaces via hexagonal architectures, enabling omnidirectional peel resistance and drainage against wet and rough surfaces, often under flowing water. In addition, an octopus has versatile suction cups with convex cup structures located inside the suction chambers for strong adhesion in various dry and wet conditions. Highly air-permeable, water-drainable, and reusable skin patches with enhanced pulling adhesion and omnidirectional peel resistance, inspired by the microchannel network in the toe pads of tree frogs and convex cups in the suckers of octopi, are presented. By investigating various geometric parameters of microchannels on the adhesive surface, a simple model to maximize peeling strength via a time-dependent zig-zag profile and an arresting effect against crack propagation is first developed. Octopus-like convex cups are employed on the top surfaces of the hexagonal structures to improve adhesion on skin in sweaty and even flowing water conditions. The amount of reduced graphene oxide nanoplatelets coated on the frog and octopus-inspired hierarchical architectures is controlled to utilize the patches as flexible electrodes which can monitor electrocardiography signals without delamination from wet skin under motion.

High adhesion and water resistance on skin surfaces are highly demanded properties for wearable and skin‐attachable electronics in various medical applications. Here, stretchable electronics with octopus‐like patterns (OPs) imprinted on a carbon‐based conductive polymer composite (CPC) film are presented. The bioinspired conductive suckers with dome‐like architectures are successfully exploited to sustain weight (500 g) in underwater, wherein this performance is known to be challenging. In addition, the artificial patch allows highly adhesive capabilities under both dry and wet conditions on various surfaces such as silicon (max. 5.24 N cm−2) and skin replica (max. 1.89 N cm−2) without contamination after detachment with an effortless peel‐off technique. The resulting device with low volumetric ratio of conductive carbon black presents sensitive and reliable piezoresistive responses to lateral strain and vertical pressure. By controlling the ratio of the carbon nanoplatelets in the polymeric matrix, electronic patch demonstrates both detection of electrocardiogram (ECG) and bending motions of wrist in dry and wet environments. Based on the characteristics shown in this work, the proposed electronic patch is a promising approach to realize wearable and skin‐attachable sensor devices for in vitro and in vivo monitoring of various biosignals.

Conductive fibers, which are highly adaptable to the morphologies of the human body, are attractive for the development of wearable systems, smart clothing, and textronics to detect various biological signals and human motions. A fiber‐based conductive sensor interconnected with hierarchical microhairy architectures, exhibiting remarkable stretchability (<200%) and sensitivity for various stimuli (pressure, stretching, and bending), is developed. For distinguishability of multiple gestures, two hierarchical hairy conductive fibers are twisted to fabricate a fiber‐type sensor, which monitors distinct waveforms of electrical signals retrieved from pressure, stretching, and bending. This sensor is highly robust under repeated appliances of external stimuli over multiple cyclic tests of various modes (<2200 cycles for each stimulus). Upon formation of a self‐assembled monolayer, it exhibits stable performance even under wet conditions. For practical applications, this sensor can be weaved into a smart glove to demonstrate a pressure and gesture‐discernible wearable controller for virtual reality (VR) interface, shedding light on advances in wearable electronics with medical and healthcare functionalities and VR systems.