There are a multitude of examples in nature of functional materials that exhibit superior properties as compared to man-made materials. Some examples of such advanced functionality are mechanical, optical, adhesive, self-cleaning, actuation and sensing properties.

It is fascinating to observe, that the common denominator of these vast designs is the use of fibers and high-aspect-ratio nano- and micro-structures. For example the superhydrophobic surface of the lotus leaf, the Gecko’s sticky feet, the fiber optical properties of the Venus’s flower basket sponge and there are many other examples.

We aspired to design a finely tunable, multifunctional, responsive nanostructured material that will show combined properties such as actuation/sensing, self cleaning, and be superhydrophobic as well.

Recently we developed hydrogel-muscle reversibly actuated Si nanostructures, which dynamically changed their orientation in response to humidity, with a 60 ms response time¹. Based on this we wanted to extend this bio-inspired design and use a materials approach to develop a low-cost procedure for producing an arbitrarily-designed actuated surface with high-aspect-ratio nanostructures that are themselves responsive to a variety of stimuli and have a finely-tuned geometry and stiffness. We have used soft lithographical techniques to replicate high aspect ratio structures from epoxy and have the ability to control the geometry of the high aspect ratio nano-posts (tilt, length and 2D array lattice and symmetry) as well as to tune the stiffness of the replicated material within 4 orders of magnitude (several MPa to a few GPa). We will present our fabrication method as well as show that these bio-inspired nanostructures can be actuated by different stimuli².

1. Science, 2007. 315(5811), 487-490.

2. Submitted to Advanced Materials (2008).

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