Adhesion Enhancement of Micropillar Array by Combining the Adhesive Design from Gecko and Tree Frog

Abstract

It has long been demonstrated the gecko‐inspired micropillar array with T‐shape tips possesses the best adhesion performance of a given material. The further enhancement of the adhesion performances of T‐shape micropillars can offer redundant adhesion to compensate for the inevitable improper contacts. Here, the array of T‐shape polydimethylsiloxane (PDMS) micropillars is incorporated with gradient dispersed calcium carbonate nanoparticles in the micropillar stalk, termed as T‐shape gradient micropillars (TG), possessing the modulus gradient with stiff tip and soft root. The gradient modulus in TG facilitates the contact formation and regulates the stress at the detaching interface, resulting in a 4.6 times adhesion and 2.4 times friction as compared with the pure PDMS T‐shape micropillar arrays. The study here provides a new design strategy for the super‐strong structured dry adhesives.

Electrochemistry‐Induced Improvements of Mechanical Strength, Self‐Healing, and Interfacial Adhesion of Hydrogels

“…As shown in Figure 4d, 0.5 h electrochemistry treating improved the adhesion energy to 200 J m −2 . Extending the electrochemistry treating time to 3 h could increase the maximum adhesion energy to 1400 J m −2 (Movie S2, Supporting Information), stronger than many adhesive interfaces that were constructed through microstructural creation on the surface (adhesion energy: 50 J m −2 ), [ 30 ] or by introduction of functional groups on the surface (adhesion energy: 418 J m −2 ). [ 31 ] In the meantime, this adhesion interaction was also higher than the bonding strength of tendons (adhesion energy: ≈800 J m −2 ).…”

Gecko’s Feet-Inspired Self-Peeling Switchable Dry/Wet Adhesive

“…It is well known that geckos can run rapidly on almost any surface due to the van der Waals force generated on intimate contact between the hierarchical microstructures (setae) on their toes and the contacted surfaces. , The rapid switch between the attachment and detachment state during locomotion is achieved by the dynamic and reversible mechanical deformation of its toes, which follows a typical peeling mechanism. , The high adhesion force, obtained when the toe is rolling in attachment, could decrease several orders of magnitude when the toe is rolling out detachment, as shown in Figure a. , Although some researchers have used a mechanical peeling mechanism to develop reversible adhesion devices, there are still several shortcomings in the reported design strategies. − First, the crack propagation mechanism between the smooth surface peeling device and the substrate limits its ability to grasp objects with curvature or roughness firmly. ,, Second, surface microstructures such as pillars and mushrooms can resist the crack propagation mechanism effectively and have a good adaptability to nonflat surfaces. ,− However, materials usually suitable for preparing these microstructured devices are chemically inert or have low surface energy (e.g., polyvinylsiloxane, polydimethylsiloxane, polyurethane, and so on), limiting their adhesion ability (especially in the wet environment). − ,− Although the negative pressure microstructure of octopus devices can adhere in the wet state, the poor crack resistance on nonflat substrates and the limitation of materials also reduce its adhesion ability. ,, In addition, almost all gecko’s feet-like switchable adhesive devices mentioned above failed under wet or underwater conditions due to the limitations of their materials. Surface modification of microstructures and coatings mentioned above can improve their adhesion ability, ,,, but these studies only focused on the combined effect of the microstructure and surface chemistry (molecular design), neglecting the role of mechanical deformation and peeling mechanism.…”

Bioinspired Hierarchical Structures for Contact‐Sensible Adhesives

“…To date, strong adhesion can be achieved in manufactured adhesives by employing delicate structures of different shapes (e.g., pillar, [ 26 ] wedge, [ 27 ] spatula, [ 28 ] microsuction, [ 29 ] funnel, [ 30 ] and mushroom [ 31–35 ] ) and materials (e.g., polyurethane, [ 29 ] polyvinylsiloxane, [ 31 ] silicone rubber, [ 33,36 ] hydrogels, [ 37 ] and nanocomposites [ 12 ] ) with homogeneous, layered, [ 38–40 ] and even gradient material properties. [ 41–43 ] Nevertheless, this is a passive strategy due to the lack of detection or feedback on the contact interface. In contrast, biological systems use the so‐called active strategy to realize a fast adhesion‐based locomotion by sensing the contact status in real‐time.…”