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Synthetic setae emulate the setae found on the toes of a gecko and scientific research in this area is driven towards the development of dry adhesives. Geckos have no difficulty mastering vertical walls and are apparently capable of adhering themselves to just about any surface. The 5-toed feet of a gecko are covered with elastic hairs called setae and the end of these hairs are split into so-called spatulas (no doubt because they carry a resemblance to actual spatulas). The sheer abundance and proximity to the surface of these spatulas make it sufficient for Van der Waals forces alone to provide the required adhesive strength 1.
One experimental inroad to artificial setae is provided by nanotubes. In one particular scheme 2 a thick layer of nanotubes is embedded in a polymer matrix and the adhesive force is calculated to be 200 times that provided by the gecko hairs. These multi walled nanotubes (MWNT) are generated by chemical vapour deposition with xylene as a carbon source and ferrocene as a catalyst and exposure of 10 minutes to 800 ░C on a quartz or silicon substrate. The nanotubes have a diameter of 1 to 2 nanometres and a length of 65 micrometres. They are dipped into a solution of methyl methacrylate with azobisisobutylonitrile as a catalyst and 1-decenethiol as a chain transfer agent and polymerized to PMMA at 50 ░C for 24 hours. The top is then etched away by immersion with a solvent like acetone exposing the MWNT hairs. In the final step the artificial skin and hairs are stripped from the silicon or quartz substrate. Scanning probe microscopy provides a means to measure adhesive force.
Researchers at Stanford University have created a robot which uses synthetic setae in order to scale walls just as a gecko would.3.
- 1 Evidence for van der Waals adhesion in gecko setae Kellar Autumn, Metin Sitti, Yiching A. Liang, Anne M. Peattieći, Wendy R. Hansen, Simon Sponberg, Thomas W. Kenny, Ronald Fearing, Jacob N. Israelachvili, and Robert J. Full PNAS August 27, 2002 Online Article
- 2 Synthetic gecko foot-hairs from multiwalled carbon nanotubes Betul Yurdumakan, Nachiket R. Raravikar, Pulickel M. Ajayan and Ali Dhinojwala Chemical Communications, 2005, (30), 3799 - 3801 Abstract
- 3 http://www.newscientisttech.com/channel/tech/mg19025526.500.html