Surfaces inspired by nature from the 3D printer

The structure of the surface of its wings gives the morpho butterfly its blue color.
 Credit: Pixabay, Garoch

Using laser radiation, researchers can print tiny structures with the highest precision. A method to imitate the superpowers of animals and plants and to make them accessible to technology.

In order to survive even in extreme habitats, many animals and plants have developed skills in the course of evolution that are only known from superheroes from films. They are mostly based on the extraordinary properties of their surfaces. The imitation of these properties holds great potential for technology to develop new products or to solve technical problems. A research team from Bochum and Kiel has succeeded in imitating the structural color of the famous blue Morpho butterflies using high-precision 3D printing technology. The researchers report on their findings on the so-called two-photon polymerization, or 2PP for short, in the Journal of Optical Microsystems from 2nd. September 2022.

Researchers from the Chair of Laser Application Technology at the Ruhr University Bochum (RUB) led by Prof. Dr. Andreas Ostendorf and Prof. Dr. Cemal Esen and the working group "Functional Morphology and Biomechanics" of the Christian-Albrechts-University in Kiel (CAU) by Prof. Dr. Stanislav Gorb involved.

3D printing for the production of biologically inspired fir trees

The 3D printing technology two-photon polymerization enables the production of complex structures on a micro and nanometer scale in order to imitate the extraordinary abilities of animals and plants for technical purposes. The picture shows the imitation of the tiny fir trees, which give the Morpho butterflies their color.
Credit: Zyla et al.

The 2PP is a laser-based printing process that enables three-dimensional processing of light-sensitive resins. Unlike conventional printing techniques, it is possible to implement complex 3D structures using virtual computer models without using support structures. In this context, individual structural features can be up to less than 100 nanometers. This corresponds to about a thousandth of the thickness of a human hair.

Thanks to the 2PP printing technology, the researchers were able to produce hierarchically constructed structures at the micro and nanometer level in order to imitate the structure color of the blue Morpho butterflies together with their extraordinary optical properties. In the butterflies themselves, the color is caused by tiny, fir tree-like structures on their wing surface. Complex physical phenomena between light and the fir trees also make it possible to perceive the blue color almost regardless of the angle. "This is astonishing in that color usually appears rainbow-like when it arises from similar physical phenomena, such as light refraction on structures," says co-author Gordon Zyla.

Biologically inspired structural colors for security against counterfeiting

Color is created by hierarchically structured structures: the result for a morpho-didius butterfly (left) and for biologically inspired structures (right), produced by means of two-photon polymerization. Credit: Zyla et al.

In the current work, the researchers were able to redesign the structures inspired by the butterflies in such a way that the resulting insensitive blue color can be observed evenly or only from certain directions. For this purpose, they first analyzed the optical properties and morphology of the wing surface of one Morpho-didius-Butterfly on the CAU. From this they deduced that they can control the direction in which the angle-insensitive color appears by changing the geometry of their previously developed structures only on the microscale, but still imitating the structures of the butterfly on the nanoscale.

The new designs proposed by the authors are suitable, for example, for the production of highly complex counterfeiting protection features. Her work also shows the great potential of the 2PP process in the biomimetics research area. By using new types of light-sensitive materials, a wide variety of functional structures from nature could be examined in this way for their use in technology. Superpowers in the animal and plant kingdom include improved adhesion or special wear resistance to various other surfaces, super hydrophobicity, which can be observed with the lotus effect, or certain colors, which are used as warning signals, for camouflage or intrasexual communication.

Source/Credit: Ruhr University Bochum

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