Biomimetic Microstructured Hydrogels with Thermal-Triggered Switchable Underwater Adhesion and Stable Antiswelling Property

Abstract

The design of hydrogels with switchable adhesion and stable antiswelling property in a wet environment has remained a challenge. Here, we report a biomimetic hydrogel that can adhere and detach on-demand on various material surfaces, which is realized by thermal-triggered switchable shape transformation on hexagonal micropillar patterned hydrogels. The hydrogels are cross-linked by two cross-linkers of poly­(ethylene glycol) dimethacrylate and 2-ureidoethyl methacrylate, which guarantee the strong mechanical property and stable antiswelling property in a wet environment. The hydrogels can maintain stable water content in solutions with variable pH, temperature, and salt concentration, and the change in volume does not exceed 2%. In addition, due to the dynamical hydrogen bonds and dipole–dipole interaction in the hydrogels, the hydrogels exhibit a thermal-triggered shape-memory effect. The hydrogel can recover shape more than 80% in 15 s. Furthermore, inspired by the surface structure of tree-frog footpads, the hexagonal micropillar patterned hydrogels exhibit improved underwater adhesion strength. The underwater adhesion strength of hexagonal micropillar patterned hydrogels is seven times more than that of flat hydrogels. Based on the shape-memory effect of hydrogels, the adhesion strength can be altered by a thermal stimulus. The adhesion strength of the microstructures recovered from the hydrogel surface decreased to 15.4% of the initial adhesion strength. The switchable underwater adhesion of hydrogels can be applied in the fields of transfer printing, medical adhesives, mobile robots, etc.

Hydrogels for underwater adhesion: adhesion mechanism, design strategies and applications

“…26 The biomimetic microstructure works well in repelling the hydration layer. 38,39 The design of the biomimetic microstructure is inspired by the adhesive disc of the clingsh and the surface structure of tree-frog footpads, both of which possess hexagonal microstructures that can quickly repel the hydration layer. Therefore, the hydrogel and the adherend are in direct contact, which increases the actual contact area between the hydrogel and the adherend (Fig.…”

Patterning meets gels: Advances in engineering functional gels at micro/nanoscales for soft devices

“…Additionally, a microstructured shape memory hydrogel was demonstrated to realize switchable underwater adhesion triggered by heat-induced shape transformation. 100…”

“…Inspired by the adhesive disk of clingfish, microsturctured polyampholyte hydrogels could enable rapid water drainage at the microstructure interface, meanwhile the dynamic ionic bondings could facilitate interfacial bridging and energy dissipation during detachment. Additionally, a microstructured shape memory hydrogel was demonstrated to realize switchable underwater adhesion triggered by heat‐induced shape transformation 100 …”

Application and Development of Shape Memory Micro/Nano Patterns

“…[68][69][70][71] Moreover, they behave well in the switchable underwater adhesion. [72] Among these applications, array of micropillars is the most widely investigated in the field of wettability. As shown in Figure 4A, micropillars have different wettability under different tilt angles and arrangements.…”

“…Shape memory micro/nanopatterns have greatly promoted the development and application of polymer materials. This review mainly introduces various shapes of SMP micro/ [58][59][60][61][62][63][64][65][66][67]94,112] Array of micropillars Acrylate-based SMP, PCL, PDLLA, epoxy-based SMP, hydrogel Thermal-induced, magnetic induced, light-induced Replica molding, thermalembossing, laser ablation Biomedicine/smart wettability/ microoptics/smart adhesive [29,30,63,[68][69][70][71][72][73]95,96,99,113,117,118,[121][122][123][124][125][126][127][128][129][130][131][132][133]142,144] Microwells PCL, PCO Thermal-induced Thermal-embossing, breath figure…”