Engineering from nature
Following the previous series that looked at stress analysis in varying sports equipment, this week starts a new series that will look into the new field of biomimicry. Biomimicry, as the name suggests is an examination of nature’s models, systems, processes and elements to help solve human problems. This week’s blogs will look at the temporary adhesive pads that are seen in gecko’s feet. The technology to temporarily stick to a surface was invented in the 1980’s when the “Post-It” note hit the market. However, nature had solved this problem millions of years ago as is seen in the foot pads of many different species of geckos. Until recently, scientists had no way to understand how the gecko was able to resist gravity and walk up walls. That is because nature structures its systems on a nanoscale, and only since about 1990 have the tools to examine these properties been available.
Engineering mechanics behind it
Looking at a human hand there are many ridges and lines that form our own unique fingerprint. These indentations largely increase the surface area of the hand and allow us the ability to hold or grasp things. Similarly, the foot of a gecko is covered with about a billion little hairs known as spatula, each no more than 200 nanometers long or wide. By comparison, a human hair is estimated to be 100,000 nanometers wide. These spatula work like Velcro when they contact a surface; by being so small that they can wedge between the atoms of a surface they are able to form molecular bonds with the surface.[ii] About 1,000 of these spatulae are arranged into groups called setae with these groups being arranged in rows which are actually visible without a microscope. In addition to having the spatulae, there is a soft pad with similar properties to silicon rubber that is permanently wetted by mucus that fills the channels in between the setae and allow for wet adhesion. Simply by will the gecko can attach the pad and resist up to 15 Newton’s of force pulling it off of the wall, and also by force the gecko can release its grip and walk with ease against gravity.
Applications and innovation
Engineers have been working on utilizing this technology to create new products. One current item on the market that utilized the material properties of gecko’s feet is known as Geckskin™ produced by a group of polymer scientists from the University of Massachusetts. This simple product is a 16 inch square that can hold up to 700 pounds of force and be removed with ease. The product utilizes an adhesive that is embedded with a soft pad and integrated into a stiff fabric; the main polymer at work is known as polydymethylsiloxane (PDMS).[iii] Another similar item is a product out of Stanford known as gecko tape, where just like geckos form a weak intermolecular bond to be super sticky at one moment, but not at the next. Engineers are looking at future project to increase the scale at which these adhesive pads are made. The goal is to create foot and hand pads that would allow human to completely free climb the side of a skyscraper, similar to the idea seen in the latest Mission Impossible™ movie. The current prototype uses Van Der Waals bonding with PDMS to allow the TBCP-II robot to climb a vertical glass wall, but has not yet been proven to work with a human because of the weight versus the contact area that a human body allows. Biologists, materials scientists and engineers have made great strides in this field to date, but the possibilities of what we can learn and develop from nature are almost endless. Electrical engineers in the fields of robotics have discovered the value of mimicking creatures of nature to design many different types of robots used in applications that range from personal home use to the battlefields of war.
As we move forward in this series, we will discuss some of the innovations and applications of biomimetics. We will look into ways that it has improved our way of life as we move forward further into the twenty first century.
[i] Bhushan, Bharat “Mechanical Engineering: The Magazine of Asme” Nature’s Nanotechnology Vol. 134/No. 12 December 2012, pg. 28
[ii] Carey, Bjorn “Live Science” Nature’s Velcro Lets Geckos Walk on Ceilings, 10 November 2005
[iii] Kaye, Leon “Triple Pundit” Gecko Feet Inspire a New Adhesiv, 20 March 2012