Peter Forbes

Gecko Update

To bring a new technology to mass market can take up to 40 years. When I wrote The Gecko’s Foot (2005), I commented that predicting which bio-inspired technologies would come good and when was the toughest job. Bringing products to market is actually harder than innovating in the first place. The clear frontrunner of the technologies featured in the book has been Lotus Effect applications. The Lotus Effect spawned a new science of super-wetting and super non-wetting materials and new applications that have emerged since the book were featured in my Scientific American article in August 2008. In the last year the greatest strides have been made in gecko adhesion itself. Several labs are working on this and are making great progress.

While I was writing the book, I had the idea of making gecko-like arrays using carbon nanotubes and suggested this to Dr Binqing Wei at Louisiana State University. Unfortunately the nanotube idea is so obvious that many others had drawn the same conclusion: nanotube arrays are now widely used to mimic the gecko and are achieving good results.  Another Chinese team at the universities of Akron, Dayton and the Georgia Institute of Technology has created a nanotube array that mimics the real geckos in the important aspect of having a thicker spatulate end to the very thin fibres. They can create 10-100 billion such fibres per square centimetre. These arrays have strong adhesion when pulled along the line of the object they are stuck to but they release easily when pulled away from the surface, exactly what you want in a reusable adhesive.

The original gecko-array fabricator, Ron Fearing, at University of California, Berkeley, has also now produced an array that mimics the gecko’s directionality, using polypropylene fibre.

One of the most fascinating ideas is to combine the techniques of the two very different creatures with remarkable adhesive properties:  geckos and mussels. Mussel glue sets underwater: it evolved that way because that’s where mussels live. Mussel glue research goes back as far as the gecko’s and in 2007 Philip Messersmith's team at North-western University, Illinois reported ‘A reversible wet/dry adhesive inspired by mussels and geckos.’ They call it ‘geckel’. It sounds an idea almost too good to be true. A gecko-like array of tiny pillars is capped with a synthetic mussel-type polymer. The result works in both wet and dry conditions and maintains its strength for 1000 cycles.

Which technique will win through: carbon nanotubes; geckel or directional polypropylene arrays? Or maybe all or none of the above? What is clear is that gecko’s foot adhesives have reached a very interesting  stage of their career.

 

Leave a Reply