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.
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 systems have become important to address the issues of human–machine interactions by smart outer/inner organ‐attachable devices for diagnosis and therapy. Here, advances in designs of biologically inspired adhesive architectures are reviewed in terms of distinct structural properties, attachment mechanisms to biosurfaces by physical interactions, and noteworthy fabrication methods. Recent demonstrations of bioinspired adhesive architectures as adhesive layers for medical applications from skin patches to multifunctional bioelectronics are presented. To conclude, current challenges and prospects on potential applications are also briefly discussed.
Nature has inspired various developments of hierarchically structured adhesive architectures for clean, reversible attachment to skin or organs within the human body. Recent progress in biologically inspired adhesive architectures is reviewed, from their geometric, material features, fabrication methods, and various medical applications from skin patches for wound protection to integrated bioelectronics with diagnostic and therapeutic functionalities.
(SH) is a seaweed that has several features that benefit health. In this study, we investigated the immune-enhancing effect of SH, focusing on the role of spleen-mediated immune functions. ...Chromatographic analysis of SH identified six types of monosaccharide contents, including mannose, rhamnose glucose, galactose xylose and fucose. SH increased cell proliferation of primary cultured naïve splenocytes treated with or without cyclophosphamide (CPA), an immunosuppression agent. SH also reversed the CPA-induced decrease in Th1 cytokines. In vivo investigation revealed that SH administration can increase the tissue weight of major immune organs, such as the spleen and thymus. A similar effect was observed in CPA-injected immunosuppressed BALB/c mice. SH treatment increased the weight of the spleen and thymus, blood immune cell count and Th1 cytokine expression. Additionally, the YAC-1-targeting activities of natural killer cells, which are important in innate immunity, were upregulated upon SH treatment. Overall, our study demonstrates the immune-enhancing effect of SH, suggesting its potential as a medicinal or therapeutic agent for pathologic conditions involving immunosuppression.
Mesenchymal stem cells such as human adipose tissue‐derived stem cells (hADSCs) have been used as a representative therapeutic agent for tissue regeneration because of their high proliferation and ...paracrine factor‐secreting abilities. However, certain points regarding conventional ADSC delivery systems, such as low cell density, secreted cytokine levels, and cell viability, still need to be addressed for treating severe wounds. In this study, we developed a three‐dimensional (3D) cavity‐structured stem cell‐laden system for overdense delivery of cells into severe wound sites. Our system includes a hydrophobic surface and cavities that can enhance the efficiency of cell delivery to the wound site. In particular, the cavities in the system facilitate hADSC spheroid formation, increasing therapeutic growth factor expression compared with 2D cultured cells. Our hADSC spheroid‐loaded patch exhibited remarkably improved cell localization at the wound site and dramatic therapeutic efficacy compared to the conventional cell injection method. Taken together, the hADSC spheroid delivery system focused on cell delivery, and stem cell homing effect at the wound site showed a significantly enhanced wound healing effect. By overcoming the limitations of conventional cell delivery methods, our overdense cell delivery system can contribute to biomedical and clinical applications.
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.
Highly air‐permeable, water‐drainable, and reusable skin patches with enhanced omnidirectional peel resistance and pulling adhesion, inspired by the toe pads of tree frogs and convex cups in the suckers of octopi, are presented. These patches are utilized as flexible electrodes by coating reduced graphene oxides to monitor electrocardiography signals without delamination on skin in sweaty and even flowing water conditions.
Mimicking the attachment of octopus suction cups has become appealing for the development of skin/organ adhesive patches capable of strong, reversible adhesion in dry and wet conditions. However, ...achieving high conformity against the three-dimensionally (3D) rough and curved surfaces of the human body remains an enduring challenge for further medical applications of wound protection, diagnosis, or therapeutics. Here, an adhesive patch inspired by the soft wrinkles of miniaturized 3D octopus suction cups is presented for high drainability and robust attachment against dry and wet human organs. Investigating the structural aspects of the wrinkles, a simple model is developed to maximize capillary interactions of the wrinkles against wet substrates. A layer of soft siloxane derivative is then transferred onto the wrinkles to enhance fixation against dry and sweaty skin as well as various wet organ surfaces. Our bioinspired patch offers opportunities for enhancing the versatility of adhesives for developing skin- and/or organ-attachable devices.
The development of an electronic skin patch that can be used in underwater environments can be considered essential for fabricating long-term wearable devices and biomedical applications. Herein, we ...report a stretchable conductive polymer composite (CPC) patch on which an octopus sucker-inspired structure is formed to conformally contact with biological skin that may be rough and wet. The patch is patterned with a hexagonal mesh structure for water and air permeability. The patch films are suited for a strain sensor or a stretchable electrode as their piezoresistive responses can be controlled by changing the concentration of conductive fillers to polymeric polyurethane. The CPC patch with a hexagonal mesh pattern (HMP) can be easily stretched for a strain sensor and is insensitive to tensile strain, making the patch suitable as a stretchable electrode. Furthermore, the octopus-like structures formed on the skeleton of the HMP allow the patch to maintain strong adhesion underwater by easily draining excess water trapped between the patch and skin. The sensor patch (<50 wt % carbon nanotubes (CNTs)) can sensitively detect the bending strain of a finger, and the electrode patch (50 wt % CNTs with addition of Ag flakes) can stably measure biosignals (e.g., electrocardiogram signals) under both dry and wet conditions owing to the octopus-like structure and HMP.
Adhesion capabilities of various skin architectures found in nature can generate remarkable physical interactions with their engaged surfaces. Among them, octopus suckers have unique hierarchical ...structures for reversible adhesion in dry and wet conditions. Here, highly adaptable, biocompatible, and repeatable adhesive patches with unfoldable, 3D microtips in micropillars inspired by the rim and infundibulum of octopus suction cup are presented. The bioinspired synthetic adhesives are fabricated by controlling the meniscus of a liquid precursor in a simple molding process without any hierarchical assemblies or additional surface treatments. Experimental and theoretical studies are investigated upon to increase the effective contact area between unfoldable microtips of devices, and enhance adhesion performances and adaptability on a Si wafer in both dry and underwater conditions (max. 11 N cm−2 in pull‐off strength) as well as on a moist pigskin (max. 14.6 mJ peeling energy). Moreover, the geometry‐controlled microsuckers exhibit high‐repeatability (over 100 cycles) in a pull‐off direction. The adhesive demonstrates stable attachments on a moist, hairy, and rough skin, without any observable chemical residues.
Octopus‐like adhesives with meniscus‐controlled unfoldable 3D microtips are fabricated by controlling the meniscus of a precursor during simple molding process. The octopus‐like adhesives show strong dry/wet adhesion performance against silicon wafers and rough hairy skin. The idea may bring forth the development of versatile applications such as clean, conformal patches for wound‐healing, and smart skin/organ‐attachable medical devices.
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.
Skin‐attachable and water‐resistant stretchable electronics are fabricated by employing an array of octopus‐like patterns on conductive polymer composite films. The electronic patch is not only highly sensitive to strain and pressure, but also strongly adhesive on dry and wet surfaces due to the suction effect. Finally, the device demonstrates measurements of biosignals and bending motions in underwater environments.
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•The insect-inspired polymeric bio-adhesive exhibits high adhesion onto skin and organ tissue.•Polymeric hierarchical microstructures are fabricated by modifying the surface ...properties.•The proposed bio-adhesive can enhance wet adhesion via the capillarity-assisted suction effect.•A highly conformal organ grasper is demonstrated through insect-inspired bio-adhesives.
Insect adhesion systems can enhance adhesion forces on wet or rough surfaces via oil-loadable spherical chambers and mushroom-shaped tips, enabling the achievement of an improved suction effect. In addition, highly conformal polymeric bio-adhesives with multiscale 3-dimensional (3D) architectures have been developed for stable adhesion performance on soft, wet, and non-flat skin or organ tissue. In this work, we propose a highly adaptable, biofluid-controllable, and reversible bio-adhesive with enhanced pulling adhesion and omnidirectional shear resistance. The development of this bio-adhesive was inspired by the hairy structure found in diving beetles, characterized by an oil-loadable spherical suction chamber and a mushroom-shaped tip. By investigating various geometrical and material parameters, a novel fabrication method was developed to control the diameter of the spherical chambers within the microcylinders and to create mushroom-like tips on the micropillars with 3D chambers. Owing to the capillarity-assisted suction effect and the omnidirectional shear resistance, originated from structural and materials features, the proposed bioinspired adhesive exhibits improved adhesion against dry and wet skin, as well as organ surfaces. Furthermore, diving beetle-inspired adhesives were employed on the top surfaces of a surgical grasper to utilize bioinspired architectures as highly conformal, wet-tolerant adhesive elements to minimize the damage of the engaged liver surfaces.
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