A small team of researchers from Kiel University in Germany recently developed a material that gets its grip from light. The technology relies on light-actuated grippers which are activated simply by shining a UV light on a new adhesive material. The researchers are working towards a device that will emulate the way geckos seamlessly scurry across precarious surfaces in almost any direction.
How Geckos Get a Grip
While many creatures may prefer dexterous hands or long claws to get a grip, geckos use an entirely different approach. They do not use sticky secretion suction cups or tiny hooks. Instead, geckos use an amazingly minute and compact array of microscopic hairs. The hairs give them their remarkable grip which enables them to scale walls and dart across ceilings at virtually any angle on virtually every surface. They are undoubtedly the ultimate climbers.
[Image Source: Wikipedia]
With seemingly no effort, a gecko can scurry across a vertical pane of glass and hang upside down on what seems to be just about every material. The secret to their unprecedentedly sticky grip is owed to the bundle of microscopic hairs which extend from each one of their four feet. While it might seem obvious that the hairs latch onto microscopic imperfections along surfaces that they climb, it is certainly not the only force at play. Also assisting them in their scaling endeavors is a surprising culprit, that being Van der Waals forces.
Van der Waals forces are responsible for holding together groups of atoms and molecules. Unlike covalent and ionic bonding which hold atoms together, Van der Waals forces act upon millions of atoms and molecules to hold them together as a group, like the molecules in water.
Geckos and der Waals
Electrons determine the polarity of a molecule. However, they are also moving around incredibly fast which can momentarily change the polarity of an atom or molecule. The momentary shift gives a molecule just enough time to bind to another. As Science describes;
This force comes from fluctuations in charge distributions between neighboring molecules, which need not be polar; their charge fluctuations naturally fall into synch, creating an attractive force.
It is an extremely weak force that is easy to break. That is unless you have millions of hairs to make it of use.
“Van der Waals forces are the weakest sort of interatomic forces that we have,” says P. Alex Greany, a professor of mechanical engineering at Oregon State University in Corvallis. “It’s amazing that geckos are able to use this really weak force.”
So what’s really going on?
Scientists are constantly toggling their beliefs and expertise on how geckos’ feet get a grip. Each individual species uses different techniques to optimize and adapt their climbing technique in accordance with the environment and what materials they have to climb. The hairs and feet are complex amongst the 850 known species of gecko. Naturally, there is much to learn, but scientists are honing down the techniques they use.
Currently, it is well understood that millions of microscopic hairs known as setae branch out to form billions of tiny contact points called spatulae. The branches exponentially increase the amount of contact, creating an exponential amount of Van der Waals forces, and finally giving geckos their renowned grip.
Naturally, as with many nature wonders, scientists tried to emulate the same effects with synthetic material. Scientists fascination in replicating gecko grip has yielded a few promising results. However, most techniques require heat or electricity to activate and deactivate the adhesion. It is easy to design a material that sticks. However, engineering a grip which can turn off and on willingly is an entirely different beast. Despite the mounting challenge scientists are nearing closer to dexterous grippers with their new implementation of light actuated gecko-grip material.
Geckos do it, why can’t we
Geckos walk across every surface as if it were the ground. So if they are held in place on so tight by Van der Waals forces, how can they walk so easily? The key to their dismount is their angled, microscopic toe hairs. Certain angles help latch the gecko to a surface.
According to a study published in 2014, some geckos can tweak the angles of here hair ever so slightly, making it much easier to detach. The discovery was made in 2014, so the technique has only recently been used in on synthetic versions.
Further increasing their grippy-ness spring loaded detachment mechanism launches them back into motion. The discovery is big, and now scientists are using the information to perfect their gecko tech.
Synthesizing actuated grippers
Naturally, as with many nature wonders, scientists are trying to emulate the same effects with synthetic material. The fascination of replicating gecko grip has yielded a few promising results in the scientific community. However, most of the techniques require heat or electricity to activate and deactivate the adhesion. Now, scientists are nearing closer to dexterous grippers with their new implementation of light actuated gecko-grip material.
A team lead by Emre Kizilkan at Kiel University recently developed a bioinspired adhesive material that can be controlled remotely by using UV light. The team first developed an elastic porous material (LCE, liquid crystal elastomer) which bends in the presence of UV light. The LCE was then combined with an adhesive compound to make a composite material that can control its grip with a little UV light.
Composite material bending under UV light [Image Source: Kiel University]
Using their newly developed method, the team could to precisely control the composite material to pick up and move a small glass slide. Activating the material with light enabled the team to gently pick up and place the glass without leaving a residue.
“The advantage of light is that it can be used very precisely. It is reversible, so it can be switched on and off again, and that very quickly,” says Emre Kizilkan from the Functional Morphology and Biomechanics research group under Professor Stanislav Gorb at the Zoological Institute.
Close up of adhesive material with LCE substrate [Image Source: Kiel University]
Getting a grip in the future
The researchers hope their intelligent adhesive composite material will be used to improve medical techniques and other procedures require transporting objects in the micro range. Or, as many might hope, it could be used to make the ultimate spiderman gloves. The applications are endless.
“We were able to show that our new material can be used to transport objects. Moreover, we demonstrated that the transport can be controlled very precisely with light – on a micro-level,” explains Kizilkan. Gorb adds: “We use light as a remote control, so to say. Our bioinspired adhesive material doesn’t leave any residues on the objects, either.”
The technology is impressive, however, it still proves that nature remains the mother of all engineering.