What is biomimetics?
Biomimetics: what butterflies and solar panels have in common
Fedor Senatov, Post-science
Materials scientist Fyodor Senatov — about how bone implants are made, how a skyscraper looks like a termite mound and why Leonardo da Vinci was engaged in bionics
Bionics
This is a field of science related to the repetition of natural features in technological structures. For example, when creating an airplane, you can study the wing of a bird and repeat its geometry and structure in order to observe the necessary aerodynamics.
The first person who was engaged in bionics documented was Leonardo da Vinci. In his diaries, you can see how he drew various engineering devices, inspired by the flight of a bird and other natural objects.
When designing trains, it is necessary to take into account aerodynamics. Therefore, they have an elongated shape resembling a bird's beak. Nature itself has prepared good aerodynamics for the birds so that they can cut through the air or dive for fish into the water column with the least loss in speed. So trains can move with minimal noise and minimal friction against the air.
Another example is that there are many different moves in the termite mound, which at first glance seem chaotic. But in fact, they are laid in such a way that the optimal air temperature was observed inside the termite mound, even in the heat. When designing large buildings, it is important not only to purchase air conditioners, but also to build so that there is a natural inflow of air and its circulation. Tall buildings are designed taking into account natural air ducts, like termite passages.
Biomimetics
Biomimetics explores the nuances of the structure and properties of natural materials in order to reproduce them. Natural objects have three important properties: anisotropy, hierarchy and dynamism.
Anisotropy means that an object has different properties along one direction and along the other. Imagine a bone. It has elongated pores — trabeculae. The strength of the bones along the trabeculae is higher than across. Therefore, it is much easier to break a bone across.
The second property is hierarchy. Let's look at the example of the same bone: it has small pores that pass into a network of large ones. This is the hierarchy. The same may apply to any other natural objects.
The third characteristic of natural objects is dynamism. The bone can regenerate and change with age. This characterizes the human bone in terms of its adaptation to loads, because depending on whether there are loads or not, the bone gets used to them in different ways.
If we can reproduce all three of these characteristics — dynamism, anisotropy and hierarchy — then we can say that we use biomimetic approaches.
How to replicate natural structures
The first method is direct repetition. You can take a 3D scanner, make a CT scan or an MRI of the same bone and print it on a 3D printer. This is a technological approach that has a minimum of science in it and the potential of which is expanding thanks to the development of 3D printing methods and high-precision study of structures using different microscopes.
The second is the reverse engineering method: bone microscopy is done, the chemical composition and mechanical characteristics are studied, and then these properties are reproduced on an artificial object with some improvements. This is how implants are developed.
The third is bio—inspiration: the geometry of a natural object is analyzed, and then engineers try to build this object anew. At the same time, the deep structure and other characteristics are not taken into account. This approach is more often used in design and architecture.
Butterfly wings and gecko paws
The butterfly wing analogue is one of the first approaches to creating biomimetic materials. The variety of colors on a butterfly's wing is due not to special pigments, but to micro- and nanostructures of the wing, which consist of a hierarchy of pores, holes and fibers. If you reproduce the structure of a butterfly wing on a synthetic material, you can achieve the same optical characteristics.
This is important for solar panels. Perovskites are materials for creating solar cells. If you repeat the structure of the butterfly wing in them, then you can achieve optimal light absorption characteristics, that is, the batteries will give more energy.
The second example is dry adhesives, which are needed for robotics. If you look at the gecko's foot, you can see that it consists of a hierarchy of fibers. Due to the fact that there are small villi consisting of other villi, geckos can climb even steep walls. There is no glue inside the gecko's paws, it is a dry adhesive. Coupling is due to physical interaction. It is possible to reproduce the same villi using silicone or polyurethane, creating a hierarchy of villi and their anisotropy. If such a material is attached to a robot, it will be able to climb steep walls. One of the first known robots is Gekko, created with the participation of MIT. These robots can be involved in rescue work — or just wash the windows of skyscrapers.
Segmentation
Fish have scales, crocodile skin consists of pimples, and armadillos have plates. All this is necessary for animals for protection and good mobility. Moreover, if one scale or plate is damaged, the rest is not damaged. Such a segmented structure can be used to create armor.
Yuri Estrin from Monash University in Australia has created osteomorphic blocks. Due to the geometry, the blocks firmly adhere to each other without glue or additional clips. If you assemble a plate from osteomorphic blocks and hit it, only the cube that was hit will collapse. Everyone else will hold each other like the plates of an armadillo. In this way, you can make armor consisting of small blocks that redistribute the impact.
Another interesting example of the use of natural objects is the creation of analogues of the web. In the spider's glands, the web is liquid, but as soon as the spider releases it, it hardens and stretches. Protein molecules can be stacked in the form of small crystals, or they can be chaotic. It turns out that the web is a long thread, inside of which there are more solid small segments oriented along this thread of the web. Thanks to this structure and orientation of protein molecules, the web has high strength, as well as flexibility and lightness. In terms of its strength, it can be compared with good steel samples.
About the author: Fedor Senatov — Candidate of Physical and Mathematical Sciences, Associate Professor of the Department of Physical Chemistry, Head of the educational program iPhD "Biomaterial Science" of NUST MISIS.
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