“There’s nothing in the world that hasn’t been thought of before. Invention is almost always just arranging things in a new way.”
-Van Phillips, inventor of a prosthetic leg inspired by cheetahs
One of the most beautiful things about Mother Nature is how she has learned from four billion years of evolution to carry out her tasks successfully, efficiently, and sustainably—without getting in the way of everything else. Humans, though, have a rare habit of destroying things after we use them. Take, for example, the millions of gallons of oil that have spilled into the ocean, destroying many an ecosystem to provide us with a non-renewable resource that keeps our houses warm and our cars running. Or look at the deforestation of our rain forests, which has led to the extinction of hundreds of known and unknown species for the purpose of temporarily creating a more comfortable life for us all.
Biomimetics—the study of nature to solve human problems—strives to eliminate this domineering mindset towards nature and look to her instead with respectful imitation, to improve our lives today without destroying the place that will take care of our offspring tomorrow. Over the years, remarkable achievements have been made in biomimetics, from the prosthetic leg inspired by cheetahs, to the the first flying machine which imitated the birds in the sky, to bulletproof vests fabricated using a process similar to how spiders spin their webs, and even to biologically-inspired photovoltaics from studying the process of photosynthesis. Questioning how nature solves its problems can lead us to discover answers to some of our most complicated problems. Over the next few months, you’ll see a series of posts from me about recent discoveries made by scientific groups working in the field of biomimetics. Let’s start off with a look at a remarkable discovery that was made here at UC Berkeley by a group studying the movement of the gecko.
Have you ever noticed the way a gecko manages to climb effortlessly up walls and hang down from branches with just a single toe, rain or shine? The bottom of a gecko’s toes are covered with millions of hair-like structures called setae which are several microns in size. Each seta is covered with hundreds of even smaller tips, spatulae (which are each about 100 nanometers in diameter). Individually, each seta experiences a small attractive van der Waals force pulling it towards the surface that the gecko is climbing. Since each foot has millions of setae, the small attractive forces add up to exceed the force of gravity acting on the little creature, enabling it to grip even the smoothest of surfaces. The gecko can control the flexing and releasing of the setae to obtain a tighter or weaker grip, enabling it to run in any direction—and along pretty much any kind of surface: dusty, wet, or rough. Geckos live in dirty, sandy places, yet their feet actually get cleaner as they move. Since only a few spatulae can adhere to a piece of dirt, the attractive forces between dirt particles and the setae are much weaker than the attractive forces between dirt particles and the surface the gecko is climbing. Thus, dirt particles are removed nearly effortlessly from the gecko’s feet.
A group of UC Berkeley researchers led by Professor Ronald Fearing of the Biomimetic Millisystems Lab have been inspired by these fascinating self-cleaning toes. In what they call the Gecko Adhesion Project, they have fabricated a self-cleaning adhesive made from arrays of long, slender polypropylene fibers that mimic setae but have a much heavier preload and peel strength (i.e. they’re stronger and stickier) than those of the gecko. The gecko adhesive, unlike conventional adhesive tapes, does not feel “sticky” to the touch. The adhesion is based solely on the geometry of the fibers: sliding the tape against a surface uncurls the fibers to engage the adhesive while sliding the tape in the opposite direction causes it to unstick (check out this video demonstration).
Such gecko-inspired synthetic adhesives have the potential to be fabricated from a range of materials that are environmentally friendly, economical, or resistant to high temperatures. Potential applications of gecko tape range from nanosurgery to robots to superhero suits. Perhaps one day, the adhesive will provide our friendly neighborhood Spiderman with a self-cleaning, more sustainable, and much stealthier way to climb up those tall buildings—you know, without leaving a trail of spidey-web in his path.
Lee, J., & Fearing, R. (2008). Contact Self-Cleaning of Synthetic Gecko Adhesive from Polymer Microfibers Langmuir, 24 (19), 10587-10591 DOI: 10.1021/la8021485
Lazaris, A. (2002). Spider Silk Fibers Spun from Soluble Recombinant Silk Produced in Mammalian Cells Science, 295 (5554), 472-476 DOI: 10.1126/science.1065780