Gecko Hair Manufacturing
Nature can be an inspiration for innovations in science. One such inspiration is comes from the gecko lizard which can climb on walls and ceilings of almost any suface texture. Rather than using it's claws or sticky substances, the gecko is able to stick to smooth surfaces through dry adhesion which requires no energy to hold it to the surface and leaves no residue. The dry adhesion force comes from surface contact forces such as van der Waals forces which act between all materials in contact.

The gecko's trick to sticking to surfaces lies in its feet, specifically the very fine hairs on its toes. There are billions of these tiny hairs which make contact with the surface and create a huge collective surface area of contact. The hairs have physical propeties which let them bend and conform to a wide variety of surface roughnesses, meaning that the gecko's secret lies in the structure of these hairs themselves. By studying this structure, we are able to mimic the biological structures with synthetic materials.

The structure of the biological gecko hair is very complicated as well as very miniscule. Each hair is made from multiple sections, a micro-hair which is roughly 5 microns in diameter, and atop each of these micro-hairs sit tens to hundreds of nano-hairs which are 200 nanometers in diameter (1/250th of a human hair) in a tree-like branching structure.

Goal: Develop techniques for producing synthetic gecko foot hairs with nano/micro hair heirarchy. Refine these techniques into processes which will alow for cost effective mass production. Utilize the gecko hair material to create advanced ultra-mobile robots.

Approach: Six electromagnetic coils surround a working volume, wherein the magnetic micro-robot (Mag-μBot) resides. The four upright coils create in-plane magnetic fields and gradients, while the top and bottom coils create vertical fields and gradients. Using DC in-plane fields and gradients alone cannot reliably translate a Mag-μBot, due to high stiction and friction to the surface. A nonuniform oscillating magnetic field is produced, which causes the Mag-μBot to experience a nonuniform rocking motion. This induces stick-slip behavior in the robot resulting in controllable translation. By varying the pulsing frequency and waveform shape, control of micro-robot velocity is achieved. Maximum velocities observed are typically over 50 mm/s in air (over 100 body lengths per second) and 20 mm/s underwater. A Mag-μBot is a composite of Neodymium-Iron-Boron particles in a polyurethane matrix, which is fabricated in a photolithography-based molding procedure to create large numbers of Mag-μBots. They can be fabricated to arbitrary planar shapes, with dimensions typically under 500 μm. Alternatively, a piece of bulk Neodymium-Iron-Boron can be laser cut into a micro-robot in a serial fashion. Visual servoing is possible using computer vision to track the Mag-μBot. Motion tasks can be planned and executed using path-planning techniques from a computer. Autonomous strategies can be applied to position and orient microparticles in the workspace.

Topics

• Contact Self-Cleaning of Adhesive Microfibers
• Directional Adhesives
• Hierarchical Adhesives
• Micro- and sub-micron size structures
• Dopamine methacrylamide-coated microfibrillar structures
• Micromanipulation using gecko fibers

By using our Force Characterization Systems we are able to get immediate feedback from our gecko hair samples, therefore we can rapidly evolve our designs to reach an optimal design.

Benefits: The new synthetic adhesive will have countless uses from space exploration robots to surgical applications to post-it notes. This reusable, self-cleaning adhesive material can be thought of as a one sided velcro which can stick to almost everything.

Videos: (newest to oldest)
Video 1: 30um diameter polyurethane fibers attaching to a curved glass surface.

Media Appearances:

• "Precision Control of Micro Machines" on MIT Technology Review, [link]
• "The Works: Robots" on the History Channel, September 2008, [iTunes Link]
• Engineering TV episode, "Magnetically Actuated Micro-Robots", June 2008, [Link]
• NIST Microrobotics Challenge, 2007, 2008, and 2010 [Link], [CNN YouTube Video]

Members: Uyiosa Abusomwan, Sukho Song

Past Members: Mike Murphy, Seok Kim, Burak Aksak Paul Glass, Yigit Menguc, Jiho Song


Papers:

2012

• U. Abusomwan and M. Sitti, "Effect of Retraction Speed on Adhesion of Elastomer Fibrillar Structures," Applied Physics Letters, vol. 101, 211907, Nov. 2012 link.
• Y. Menguc, S. Y. Yang, S. Kim, J. A. Rogers, and M. Sitti, “Gecko Inspired Controllable Adhesive Structures Applied to Micromanipulation,” Advanced Functional Materials, vol. 22, no. 6, pp. 1246-1254, March 21, 2012. (Appeared in the frontispiece cover of this issue)

2011

• E. Cheung and M. Sitti, "Enhancing Adhesion of Biologically Inspired Polymer Microfibers with a Viscous Oil Coating," Journal of Adhesion, vol. 87, no. 6, pp. 547-557, 2011.
• P. Glass, C. Bellini, M. Sitti, and E. S. Di Martino, "Biaxial Mechanical Modeling of the Small Intestine," Journal of the Mechanical Behavior of Biomedical Materials, vol. 4, no. 8, pp. 1727-40, Nov. 2011.
• B. Aksak, C. Y. Hui, and M. Sitti, "Effect of Aspect Ratio on Adhesion for Soft Elastic Fibers," Journal of the Royal Society Interface, vol. 8, no. 61, pp. 1166-1175, 7 Aug. 2011.
• B. Sumer, B. Aksak, K. Chuengsatiansup, K. Sahin, J. D. Taylor, and M. Sitti, "Piezoelectric Vertical Polymer Fiber Array as a Tactile Sensor," Sensor Letters, vol. 9, no. 2, pp. 457-463, April 2011.
• H. Chung, P. Glass, J. M. Pothen, M. Sitti, and N. R. Washburn. Enhanced Adhesion of Dopamine Methacrylamide Elastomers via Viscoelasticity Tuning, Biomacromolecules, 12 (2), pp. 342-347, February 2011. link.
• M. Murphy, C. Kute, Y. Menguc, and M. Sitti, ''Waalbot II: Adhesion Recovery and Improved Performance of a Climbing Robot using Fibrillar Adhesives,'' The International Journal of Robotics Research, Jan. 2011, link

2010

• S. Kim, J. Wub, A. Carlson, S. H. Jin, A. Kovalsky, P. Glass, N. Ahmed, S. L. Elgan, P. M. Ferreira, M. Sitti, Y. Huang, and J. A. Rogers, ''Microstructured Elastomeric Surfaces with Reversible Adhesion for Applications in Assembly by Transfer Printing,'' Proceedings of National Academy of Sciences USA, vol. 107, no. 40, pp. 17095-17100, October 5, 2010.
• P. Glass, H. Chung, N. R. Washburn, and M. Sitti, ''Enhanced Wet Adhesion of Elastomeric Micro-Fiber Arrays with Mushroom Tip Geometry and a Photopolymerized p(DMA-co-MEA) Tip Coating,'' Langmuir, vol. 26, no. 22, pp. 17357-17362, 2010.
• B. Sumer, C. D. Onal, B. Aksak, and M. Sitti, ''An Experimental Analysis of Elliptical Adhesive Contact,'' Journal of Applied Physics, vol. 107, no. 11, pp. 113512-8, June 2010

2009

• S. Kim, M. Sitti, Tao Xie and Xingcheng Xiao, "Reversible dry micro-fibrillar adhesives with thermally controllable adhesion," Soft Matter, Vol.5, pp. 3689 - 3692, July 2009, link.
• P. Glass, H. Chung, N. R. Washburn, and M. Sitti. Enhanced Reversible Adhesion of Dopamine Methacrylamide-Coated Elastomer Microfibrillar Structures under Wet Conditions. Langmuir, 25 (12), pp. 6607-6612, June 2009. available online.
• P. Glass, M. Sitti, A. Pennathur, and R. Appasamy. A Swallowable Tethered Capsule Endoscope for Diagnosing Barrett's Esophagus. Gastrointestinal Endoscopy, 69 (5), p. 106, Apr. 2009.
• M. Murphy, S. Kim, M. Sitti, "Enhanced Adhesion by Gecko Inspired Hierarchical Fibrillar Adhesives", ACS Appl. Mater. Interfaces, in press, 2009.
available online
• M. Murphy, B. Aksak, and M. Sitti, "Gecko Inspired Directional and Controllable Adhesion" Small, 5, 170-175, 2009. available online

2008

• S. Kim, J.-H. Jang, M. Sitti, and E. Thomas, "Fabrication of gecko foot inspired elastomer nanofibers with spatulate tips," IEEE Nanotechnology, 2008.
• S. Kim, and M. Sitti, "Fabrication and characterization of biologically inspired mushroom-shaped elastomer microfiber arrays," ASME IDETC Micro/Nano Systems, 2008.
• S. Kim and M. Sitti, "Fabrication and characterization of biologically Inspired microfiber arrays with spatulate tips," International Conference on Micromanufacturing, 2008.
• C. Y. Hui, R. Long, S. Kim, and M. Sitti, “Modeling the soft backing layer thickness effect on adhesion of elastic microfiber arrays,” Journal of Applied Physics, vol. 104, pp. 044301-044309, 2008.
• B. Aksak, M. Murphy, M. Sitti, "Gecko Inspired Micro-Fibrillar Adhesives for Wall Climbing Robots on Micro/Nanoscale Rough Surfaces," ICRA, Pasadena, CA, May 2008. [pdf]

2007

• S. Kim, B. Aksak, M. Sitti, "Enhanced Friction of Elastomer Microfiber Adhesives with Spatulate Tips," Applied Physics Letters, 91, 2007.
• M. Murphy, B. Aksak, M. Sitti, "Adhesion and Anisotropic Friction Enhancements of Angled Heterogeneous Micro-Fiber Arrays with Spherical and Spatula Tips," Journal of Adhesion Science and Technology, 21, 1281-1296, 2007.available online
• S. Kim, M. Sitti, C. Hui, R. Long, and A. Jagota, Applied Physics Letters, 91, 161905 (2007)
• B. Aksak, M. Murphy, M. Sitti, "Adhesion of Biologically Inspired Vertical and Angled Polymer Microfiber Arrays", Langmuir, 0743-7463, 2007. available online.

2006

• S. Kim and M. Sitti, ''Biologically Inspired Polymer Microfibers with Spatulate Tips as Repeatable Fibrillar Adhesives,'' Applied Physics Letters, vol. 89, no. 26, pp. 26911-13, 27 Dec. 2006. pdf
• G. Shah, M. Sitti, ''Modeling and Design of Biomimetic Adhesives Inspired by Gecko Foot-Hairs'' IEEE International Conference on Robotics and Biomimetics (ROBIO), Shenyang, China, Aug 2004. pdf
• C. Menon, M. Murphy, M. Sitti, ''Gecko Inspired Surface Climbing Robots'' IEEE International Conference on Robotics and Biomimetics (ROBIO), Shenyang, China, Aug 2004. pdf
• M. Sitti and R. S. Fearing, ''Synthetic Gecko Foot-Hair Micro/Nano-Structures as Dry Adhesives for Future Wall-Climbing Robots,'' IEEE Robotics and Automation Conference, pp. 1164-1170, Taiwan, September 2003. pdf
• M. Sitti and R. S. Fearing, ''Nanomolding based Fabrication of Synthetic Gecko Foot-Hair Micro/Nanostructures,'' IEEE Nanotechnology Conference, pp. 137-140, Washington, DC, USA, August 2002. pdf
• K. Autumn, M. Sitti, Y. A. Liang, A. Peattie, W. Hansen, S. Sponberg, T. Kenny, R. Fearing, J. Israelachvili & R. J. Full, ''Evidence for van der Waals attachment for geckos,'' PNAS, vol. 99, no. 19, pp. 12252-12256, 17 Sept. 2002. pdf

List of biologically inspired adhesive publications