Stick to it!

There is little doubt that, since its invention in the 1920s, adhesive tape in its various forms has been a great boon to mankind. Whether used to render torn banknotes back into legal tender, removing fluff from an item of clothing, providing temporary repairs to everything from car wing mirrors to the wings of aircraft or even just to stick one bit of paper to another, it has become an indispensable item in the home and workplace. However, it does have limitations. For one thing, its very nature as an adhesive substance prevents it from being used again effectively, having lost some of its adhesive properties on the surface to which it was previously adhering and also possibly as a result of picking up dirt, grease or dust that renders it less sticky. Another drawback, of course, is that normal adhesive tape cannot be used on wet surfaces, restricting its usefulness to situations where it is possible to ensure that the surface on which the tape is being placed is clean and dry. The Challenge The challenge this month, then, is to develop an adhesive tape that does not suffer these disadvantages. This new substance will have to be stronger, reusable and capable of operating in conditions in which traditional sticky tape cannot. The solution does not have to involve adhesive in the traditional sense, of course. It could involve magnets, for instance – although that would obviously present other drawbacks, not to mention limitations! Perhaps, then, some arrangement of spikes could allow the tape to the surface to which it is attached? Undoubtedly this would adhere, but the damage done to the object may make users think before deploying such a solution. As ever in the Coffee Time Challenge, we do have a particular solution in mind. In this instance, it is one that has borrowed heavily from nature in order to achieve its end. It is a dry adhesive tape that not only boasts impressive bonding strength, but can also be attached and detached thousands of times without losing its adhesive properties. This solution is ingenious, fascinating and will be revealed in our March issue, but who is to say you can't do better? -Solution- The solution to February 2012 Coffee Time Challenge The solution to this Challenge of how to improve on sticky tape comes from researchers at the Zoological Institute at the University of Kiel, who have have turned to the biology of gravity-defying ceiling walkers, such as geckos and insects. These creatures served as inspiration for a new dry adhesive tape that not only boasts impressive bonding strength, but can also be attached and detached thousands of times without losing its adhesive properties. The secret to the wall climbing ability of many insects and geckos lies in the thousands of tiny hairs called setae that cover their feet and legs. The sheer abundance of these hairs, coupled with flattened tips that can splay out to maximise contact on even rough surface areas, make it sufficient for the Van der Waals forces, which operate at a molecular level and are relatively weak compared to normal chemical bonds, to provide the requisite adhesive strength that allows them to scurry along walls and ceilings. It is this technique that the research group, led by Stanislav Gorb, have mimicked with their silicone tape. By patterning the tape with tiny hairs similar to setae, they created a tape that was at least two times harder to pull off of a surface than a flat tape of the same material. Additionally, the bioinspired tape leaves no sticky residue, can also work underwater, and can be repeatedly peeled off thousands of times without losing its ability to grip. Providing an illustration of the adhesive properties of the new tape, a 20 x 20 cm (7.87 in) square piece was able to support the weight of one team member dangling from the ceiling. The researchers are also looking to nature in the form of beetle coverwings, snake skin, and anti-adhesive plants, for inspiration for other bio-inspired materials.