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Gecko Foot-Hairs Inspired Repeatable Elastomer Micro-Fibrillar Adhesives
Micro- and nanoscale beta-keratin fibrillar structures on the feet of geckos and other climbing insects have been of great interest because they can repeatedly and strongly adhere to wide range of surfaces in various environments. In this presentation, mechanics, fabrication, characterization, and applications of elastomer fibrillar adhesives inspired by these biological foot-hairs will be introduced. Various polymer micro/nano-fiber designs are proposed and fabricated using optical lithography, dip-transfer, and molding based micro/nanofabrication techniques. First, adhesion and friction of vertical polyurethane elastomer micro-fiber arrays with mushroom like tip endings are shown to enhance adhesion and friction as strong as gecko foot-hairs on smooth and rigid surfaces. These elastomer fibers are highly repeatable ; their adhesion reduces only around 15% after thousands of attachment-detachment cycles. A water droplet is demonstrated to clean these synthetic fibers fully when they are contaminated by dirt particles. The bare fibers degrade their adhesion under water ; therefore, mussel inspired DOPA methacrylate coatings on the fiber tip endings are used to enable improved adhesion strength in such fully submerged conditions. Moreover, it is shown that fibers have reduced adhesion on smooth soft substrates due to reduced equal load sharing.
Next, hierarchical fiber arrays from millimeter scale down to molecular scale are also fabricated and demonstrated to enhance adhesion on single asperity rough surfaces. Here, ATRP process is used to graft PBA dangling chains from PDMS micro-pillars as nanoscale fibrillar structures to enhance adhesion at the molecular scale. Furthermore, oriented elastomer fibers with angled tips are proposed to enable highly directional/anisotropic friction and controlled adhesion similar to biological foot-hairs. Finally, miniature robotics (climbing robots and medical soft capsule robots) and robotic manipulation applications of these fibrillar adhesives are demonstrated. In addition to these robotic applications, these new gripping materials could have broad applications in sports, space, textile, product design, medical, and packaging industry.