ME Seminars on "Modeling “Morning Glory:” how do we develop simple analytical models for internal bores?" & "Microfabrication of Bio-Inspired Adhesive Systems"
ME Seminar Series Presents 2 Short Form Seminars:
Microfabrication of Bio-Inspired Adhesive Systems
Sathya S. Chary
Most geckos can rapidly attach and detach from almost any kind of surface using the weak but universal van der Waals forces. This ability is attributed to the hierarchical structure of their feet (involving macroscale toe pads, arrays of ‘seta’ microfibers, and nanoscale spatula tips), and how these anisotropic structures are moved (articulated) to generate strong adhesion and friction forces on gripping that rapidly relax on releasing. Inspired by the gecko adhesive system, various structured surfaces have been fabricated suitable for robotic applications.
First, vast arrays of both vertical and tilted rectangular PDMS micro-flaps were fabricated using micro-electromechanical systems (MEMS) fabrication techniques. Friction and adhesion force properties were investigated using a custom-built tester with a flat-on-flat test geometry and millimeter-scale contact area. Demonstrating the importance of both asymmetric tilted structures (such as the fibers in geckos) and an optimal articulation mechanism, it was found that the anisotropic structure of the tilted micro-flaps resulted in highly anisotropic adhesion and friction forces when articulated along different directions: high friction and adhesion when sheared along the tilt direction, and low friction and adhesion when sheared against tilt.
Then, the importance of both tilt angle and fiber shape was demonstrated with tilted half-cylinder PDMS microfiber arrays. With suitable articulation, the adhesion force was switched from a maximum of 9.4 kPa for strong attachment to a minimum of zero for easy detachment. Practical applications require adhesives to be highly durable in addition to being anisotropic – this material retained up to 77% of the initial adhesion after 10,000 test cycles.