Using design principles inspired by the nanoscopic hairs on the gecko, UC Berkeley researchers and colleagues have created a novel microfiber array which has very high friction but is not ``sticky''. Usual high friction materials, such as soft rubbers or polymers, are tacky, and would be uncomfortable on shoe soles (think gum stuck to the bottom of one's shoe). The high friction micro fiber array works by having tens of millions of contacts per square centimeter which approximate the intimate contact soft rubber has with a surface. The microfibers are made from a rigid plastic which is 100 to 1000 times harder than rubber, and can resist high temperatures without softening. The microfiber array has friction which is 10 to 30 times greater than the friction of the starting plastic. This novel material could potentially replace soft rubber on surfaces which need high friction like shoes, tires, or sport gloves.
Point of Contact
Prof. Ronald S. Fearing, UC Berkeley;
510-642-9193; ronf @ eecs . berkeley .
edu
Supported by National Science Foundation and Defense Advanced Research
Projects Agency
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  Scanning electron microscope picture of synthetic fibers which are 20 micrometers tall and 600 nanometers in diameter. (Microfibers are about 100 times smaller than a human hair.) There are approximately 40 million fibers per square centimeter (250 million fibers per square inch). |
 Scanning electron microscope picture of setae from Anolis lizard. (Picture copyright Kellar Autumn). Anolis seta are approximately the same size as the synthetic fiber array. |
Conceptual drawing showing how microfibers engage with a surface. A compressive load brings more hairs into contact, increasing true contact area. Friction increases with true area of contact.
High Friction
Friction is the force that resists sliding between two surfaces. High friction materials can prevent sliding under high loads or steep inclines. Such materials are typically soft and can achieve intimate contact with an opposing surface. A typical high friction material is rubber, which is used in a variety of applications such as shoes and tires.
The adhesive system of gecko lizards also demonstrates high friction. Unlike other high friction materials, the gecko's adhesive is composed of rigid, durable material. Intimate contact with an opposing surface is achieved through the bending of millions of compliant micro-sized hairs called setae.
Gecko-inspired High Friction
A synthetic microstructure similar to the gecko adhesive was made by casting plastic into a porous mold. This procedure yields an array of vertically aligned polymer fibers that are each less than a micron in diameter and 20 microns high (about one fifth the thickness of a sheet of paper).