In January, we noted the work of biophysicist Kellar Autumn on an improved understanding of how gecko feet could exhibit such incredible adhesive power, yet leave no residue and even clean themselves during use. Gecko feet have complex microstructures known as setae and spatulae (tiny hairs and the fringes splitting off from them) that make use of Van der Waals force to allow geckos to stick to just about anything. Autumn's ultimate goal is to devise an artificial analogue to gecko adhesion, in order to make (in his words) not just the glue of the future, but the screw of the future: a dry, ultra-strong yet readily detached as needed, residue-free adhesive that works in vacuum, underwater, and on any surface.
But Autumn isn't the only one working on that goal.
On Friday, a research team led by University of Akron polymer scientist Dr. Ali Dhinojwala announced the development of artificial setae and spatulae made of multi-wall carbon nanotubes. What's more, the geckomimetic tubes demonstrate an adhesive force substantially more powerful than gecko feet.
As they summarize in their report in Chemical Communications:
...we have successfully demonstrated that structures found in gecko feet can be fabricated on polymer surfaces by using multiwalled carbon nanotubes. These structures have remarkable adhesion forces at the nanometer level, 200 times higher than that of a gecko foot-hair, and offer excellent potential as dry adhesives for microelectronics and space applications. The polymer used is a glassy PMMA [poly(methyl methacrylite), aka Lucite] but this approach can be applied to elastomeric polymers with different moduli and flexibility. This will provide the flexibility to deform at many different length scales compared to that of gecko foot-hair. We are currently extending our procedure to optimize the nanotube structures, to obtain macroscopic contact areas with high adhesion and different polymer matrices.
As the summary suggests, while they've managed to assemble the artificial gecko hair at the nanoscale, they have yet to make the nanotube setae work at a usable size.
If this seems like just another nanotube story, think for a moment about the implications when this material moves from the research bench to store shelves. These would be adhesive devices -- bandages, "nails," fasteners, seals -- that could withstand hundreds or even thousands of pounds of pressure, but be removed easily with an appropriate twist. And when removed, there's nothing sticky left behind, and the adhesive device could be used again with precisely the same strength. Imagine being able to design something where each component could be adjusted as easily as a sticky note is moved on a sheet of paper -- and yet, in use, the components would hold together tighter than if they were bolted in place. This would be the ultimate utility for "design for disassembly," an enabler for a "cradle-to-"cradle" world.
As this research continues to accelerate, we may soon find ourselves in a world held together by artificial gecko feet.
