Flexible and Shape-Reconfigurable Hydrogel Interlocking Adhesives for High Adhesion in Wet Environments Based on Anisotropic Swelling of Hydrogel Microstructures

Abstract

This study presents wet-responsive, shape-reconfigurable, and flexible hydrogel adhesives that exhibit strong adhesion under wet environments based on reversible interlocking between reconfigurable microhook arrays. The experimental investigation on the swelling behavior and structural characterization of the hydrogel microstructures reveal that the microhook arrays undergo anisotropic swelling and shape transformation upon contact with water. The adhesion between the interlocked microhook arrays is greatly enhanced under wet conditions because of the hydration-triggered shape reconfiguration of the hydrogel microstructures. Furthermore, wet adhesion monotonically increases with water-exposure time. A maximum adhesion force of 79.9 N cm–2 in the shear direction is obtained with the hydrogel microhook array after 20 h of swelling, which is 732.3% greater than that under dry conditions (i.e., 9.6 N cm–2). A simple theoretical model is developed to describe the measured adhesion forces. The results are in good agreement with the experimental data.

Wet‐Responsive, Reconfigurable, and Biocompatible Hydrogel Adhesive Films for Transfer Printing of Nanomembranes

“…The changes in PEGDMA nano‐ or microstructures before and after swelling are shown in Figure b. To visualize the microstructural change, PEGDMA with a high MW of ≈6000 was utilized because hydrogels with higher MWs undergo a more noticeable volume expansion upon swelling . As can be seen, the swollen PEGDMA had more expanded and porous structures compared to the dried PEGDMA.…”

Bioinspired Multiscale Wet Adhesive Surfaces: Structures and Controlled Adhesion

“…Jeong et al designed adhesive microhooks that function by mechanical interlocking and derived the corresponding theory according to the force balance between the microhooks. The normal and friction forces are shown as follows where n and θ m represent the tilting angle and number of the microhooks, f 1 and f 2 represent the frictional forces on the interlocked microhooks, F x and F y are external forces along the direction of x ‐ and y ‐components, the bending force on the tips and adhesion force between the tip and the bottom substrates are represented by F b ,t and F ad , respectively. Furthermore, the test results of the adhesion of the microhooks were verified by the above theory, showing a high correlation.…”

“…Using the hooks and setose pads, teleost and mayfly larvae achieve underwater adhesion for fixation by employing the mechanical interlocking and friction strategies supplying us inspiration for fabricating wet adhesive surfaces. For instance, poly(ethylene glycol) dimethacrylate microhooks show greatly enhanced wet adhesion between two layer of microhooks due to shape‐reconfigurable triggered by water . Later, poly(urethane acrylate) (PUA) microhooks form a robust mechanical interlocking system, exhibiting strong and reversible adhesion taking advantage of physical interlocking .…”

“…Recently, responsively reversible wet/dry adhesive surfaces under the external stimuli such as temperature,4b,12 light, humidity, electric,87c and magnetic have attracted the attention of researchers for their tunable and reversible adhesion performance. For instance, Wang et al developed micropillar structured surfaces with self‐assembly of pDOPA‐AD‐MEA and pNIPAM‐CD, which show reversible and tunable properties on different substrates because of the host–guest interaction and thermoresponsiveness 4b.…”

Controlled Adhesion Anisotropy between Two Rectangular Grooved Surfaces

“…With this method, the high‐aspect‐ratio shape–memory pillar surface, carbon nanotube array surface, hybrid Ge/parylene nanowire surface, microtrichias surface, micro polymeric rectangular parallelepiped array surface, and reconfigurable microhook array surface can achieve a high normal or shearing adhesion force of tens of kPa . By utilizing the swelling of hydrogel material in wet environments, an ultrahigh normal adhesion strength of 140 kPa and a shearing strength of 800 kPa can be achieved with the mushroom‐shaped hydrogel microstructure . In macroscale, a commercial adhesive strip (Command brand, produced by 3M Co., Ltd.) makes two same millimeter‐scale mushroom‐shaped pillar array surfaces engage into each other to obtain a firm adhesion .…”