An intelligent, adhesive composite material, similar to the adhesive mechanisms that allow geckos and other animals to walk upside down or cling to a wall, has been developed and it can be controlled using light. Scientists at Kiel University created the artificial, microstructured transport device that can be remotely controlled using UV light, making it possible to precisely transport objects in a micro-range. The new composite material consists of two substances: an adhesive material (blue) and an elastic LCE (liquid crystal elastomer) plastic (yellow). LCE is made up of azobenzene molecules that bend — thus bending the whole material — when they are irradiated with UV light. The curvature causes the adhesive elements to detach from the object. Courtesy of Emre Kizilkan and Jan Strueben. "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 can be done very quickly," said researcher Emre Kizilkan. The scientists first developed an elastic porous material — liquid crystal elastomer (LCE) — which bends when illuminated with UV light for its special molecular structure. Then they noticed that the more porous the material, the more it bent. Kizilkan and fellow researchers made use of this fact. "Due to their structures, porous materials can be very easily incorporated to other materials," said Kizilkan. "So we tested what happens when we combined the elastic material, which reacts well to light, with a bio-inspired material that has good adhesive properties." This resulted in an intelligent, adhesive composite material that can indeed be controlled by light. The surface consists of mushroom-shaped adhesive microstructures, similar to those found on the feet of some species of beetle. Flat or three-dimensional small elements such as microscope slides or glass spheres can attach and be picked up. When the composite material is illuminated with UV light, it bends. Because of the bending of the surface, more and more adhesive elements detach from the object, until it can finally be dropped down again. "We were able to show that our new material can be used to transport objects,” said Kizilkan. “Moreover, we demonstrated that the transport can be controlled very precisely with light, on a micro-level.” When illuminated with UV light, the intelligent material with the adhesive surface bends. This way it can lift, transport and put down flat and three-dimensional objects like this 1-mm-diameter glass sphere. Courtesy of Emre Kizilkan. Through tunable ultraviolet light illumination, the adhesive ability of this bio-inspired transport device was reduced up to a factor of 2.7 in terms of adhesive forces and was quickly recovered when the light stimulus ceased. The findings could be used for future applications in the fields of robotics, industry and medical technology. It also has possible uses in building sensitive sensors and micro-computer chips. The Kiel-based research team's results were published in the scientific journal Science Robotics (doi: 10.1126/scirobotics.aak9454).