Fabrication of Bio-Inspired Actuated Nanostructures with Arbitrary Geometry and Stiffness
Wiki entry by : Dongwoo Lee, AP225 Fall 2010.
Paper in this Wiki : Fabrication of Bio-Inspired Actuated Nanostructures with Arbitrary Geometry and Stiffness, B. Pokroy, A. K. Epstein, M. C. M. Persson-Gulda, J. Aizenberg, Adv. Mater., 2009, 21, 463-469.
The paper describes the fabrication method of high aspect ratio pillar structure which is inspired by biology. (This structure is utilized by creatures such as Gecko lizard to create sticking force between vertical surface and his foot pad.) The main advantage of this method is that it can produce low cost pillar structure with variety materials and orientations. In this work, PDMS was used as a mold not as the final structure. Fig. 1. shows the fabrication procedure. Si nanoposts were fabricated first then PDMS was poured on it. Now, one can change the orientation (Fig.2) of the holes in the PDMS mold to cast the final structure with desired orientation and material. (With various materials, the authors could create the pillar structures with a stiffness that ranges from 1MPa to several gigaPascals.) The authors investigated the actuation ability of the structure. (fig. 3) The actuation is driven by the electrostatic forces imposed by the e-beam. The movement is reversible and can be repeated multiple times.
Soft Matter Discussion
The paper talks about a creative and simple method to fabricate bio-inspired pillar structure. Compared to the previous works, this work made it possible to fabricate multi-matarial and multi-oriented pillar structure that more resembles to the counterparts in real world. One can improve the functionality of the structure introducing hierarchical structures. In real Gecko lizard's foot pad, there are multi scale structure to make it stick to the wall as close as possible. Also, more kind of materials can be casted in the PDMS mold once the knowledge about material compatibility is clear. Last, to make the structure have the sensing ability as fish can sense the flow with its micro pillars on its skin, optics knowledge can be utilized. In robotics. This concept was implemeted in a robotics paper. 
 Yong-Lae Park, Kelvin Chau, Richard J. Black and Mark R. Cutkosky, Force Sensing Robot Fingers using Embedded Fiber Bragg Grating Sensors and Shape Deposition Manufacturing, 2007 IEEE International Conference on Robotics and Automation Roma, Italy, 10-14 April 2007