Moisture harvesting lizards are specialists in surviving in extremely dry environments. The finest surface structures of their skin allow them to retain water and to directionally transport it across their body. As part of the EU’s LiNaBioFluid project, it has been possible to transfer these structures to technical surfaces and to test their functionality in other areas of application.
Friction causes wear. The uneven wetting of a surface with lubricant causes excessive wear or increased energy consumption in many industrial applications. Reworks that counteract this problem are often only possible by resorting to complex procedures. The search for a solution warrants thinking outside the box. The animal world already holds solutions to similar problems. "The idea of the LiNaBioFluid project is to observe nature and to reproduce functionalities that nature creates on animals such as lizards on technical surfaces", explains Dr. Jörn Bonse from the Nanomaterial Technologies Division, who, together with his colleague Dr. Sabrina Kirner, links lizard skin and surface structures. When certain types of lizards walk through the damp desert sand in the morning, they can retain small amounts of water on their skin and transport it along their legs and across the back to the mouth. This is enabled by a specific surface microstructure of their skin. In order to transfer these structures to technical surfaces, BAM’s researchers use a laser that emits extremely short light pulses whose duration is in the range of a quadrillionth (10-15) part of a second. This is called a femtosecond laser. "BAM has had extensive expertise in material processing with ultrashort laser pulses since the beginning of the nineties. In recent years, research has advanced steadily towards surface structuring with micro and nanostructures", says Bonse.
Seven partner organisations striving for one goal
A special feature of the LiNaBioFluid project is the strong interdisciplinary collaboration between researchers in the fields of biology, materials science, chemistry and physics. An interdisciplinary consortium from four European countries are working together for the success of the project. There are seven partner organisations from Greece, Spain, Germany and Austria, as well as a company from the private sector. In 2016, the Aachen and Linz project partners received the renowned "International Bionic Award" of the Schauenburg Foundation for their outstanding research work. The LiNaBioFluid project runs for three years and is funded by the European Union. BAM’s task in this EU project is the micro- and nanostructuring of technical surfaces using femtosecond lasers. "In cooperation with the Macrotribology and Wear Protection Division, we are also testing the resulting structures for their tribological performance, thus checking if various lubricants can minimise friction and the associated wear", explains Bonse and adds: "The project has tremendous technological potential in terms of increasing the durability of surfaces rubbing against each other and a possible reduction of energy losses."
The project has a strong biological impact and therefore benefits enormously from the expertise of the corresponding university project partners in Linz and Aachen. "The biologists provide us with images and models of the surfaces of animals as they exist in nature. We transfer these to technical materials through laser structuring. For this purpose, the institutes involved use various ultrashort pulse laser systems and also different process strategies. Project partners in Greece are also investigating the wetting behaviour of such laser-structured surfaces with different liquids such as water and oil” – explains Dr. Sabrina Kirner on the interdisciplinary cooperation.
From research to application
The first research step involved the transfer of abstracted structures at a laboratory-scale to various metal samples. Bonse explains: "We use the lasers to create different types of surface structures in the nanometre and micrometre range. In terms of their characterisation, we are fortunate to have excellent cooperation between the Divisions and that we can use the surface analysis methods and the expertise of participating colleagues in the Materials Protection and Surface Technology Department. We benefit enormously from BAM’s excellent equipment."
Scientists from Spain, Germany, Greece and Austria are currently transferring these laboratory results to larger, industrially relevant areas and testing their properties. The research results are of particular interest to the mechanical engineering and automobile industries.
The idea of the EU’s LiNaBioFluid project (Laser-induced Nanostructures as Biomimetic Model of Fluid Transport in the Integument of Animals) is to use lizards and bark bugs as models of nature to functionalise technical surfaces.
The unique wetting properties of the outer shell of both animals enable fluids to be transferred in a directional manner. Lizards living in drought (e.g. deserts) are capable of transporting fluids through fine capillaries unidirectionally to the mouth. Bark bugs, on the other hand, use wetting with water for camouflage in order to adapt to the natural environment in the event of rain through a darker colouration or even to distribute oily defence secretions.
The aim of the project is to simulate these effects on technical surfaces. To harness the biomimetic structures for industrial applications, BAM uses ultrashort pulse lasers to create hierarchical micro- and nanostructures on different materials through direct structuring and self-assembly. The optimised surface and wetting properties could, among other effects, reduce friction and wear when using liquid lubricants.
The interdisciplinary consortium of the LiNaBioFluid project consists of seven partners from four different countries. Aside from BAM, these are:
The project is funded under the EU's Horizon 2020 FET Open programme (grant number: 665337).