The tribological performance of a product and its internal components is important for extending its lifespan, limiting wear and breakdowns, or simply preventing mechanical losses due to friction.

Despite past improvements, further progress is still needed, particularly regarding friction surfaces. In the automotive industry, for example, it has been estimated that 17% of combustion energy is lost to internal mechanical friction. All parts of the drivetrain are affected: from the engine to the wheels, including the transmission.

Any improvement would also help reduce noise emitted by a product or internal component, and even compensate for heat loss.

Nature, an expert in friction, lubrication, and energy saving, possesses extensive know-how in this field.

To move, species must employ efficient techniques to minimize the energy they use. Whether on land or at sea, living things are experts at minimizing friction: their drag must be reduced to the maximum.

Lubrication and wear reduction techniques are an art mastered by living beings. To guarantee their survival and physical integrity, they must minimize damage caused by contact with the external environment.

To feed themselves, living things have also developed formidable techniques of predation and capture: nature abounds with ruthless and inescapable traps based, among other things, on exceptional lubrication properties.

As specialists in the field, Bionnov explains why and how biomimicry enables the development of new approaches and technologies in tribology. We present a selection of compelling examples.

Nepenthes Alata: the art of creating non-stick surfaces.

Carnivorous plants feed on insects, which serve as a source of nutrition. Each species has developed its own remarkably effective technique for attracting, capturing, and digesting its prey. Nepenthes alata is one such species with a particularly effective capture strategy.

At the end of each leaf is a pitcher that can reach several tens of centimeters in length, and which constitutes a formidable trap for every insect.

The trap's entrance is covered in nectar that attracts them and leads them directly into the pitcher, where the walls are so slippery that they cannot grip them to escape . The insects then fall into the digestive zone where they are quickly anesthetized and then dissolved.

Where do these anti-stick properties come from? The internal walls of the slippery zone are super-hydrophobic and microscopically rough: they are covered with wax crystals that prevent insects from attaching to them.

The company Adaptive Surface Technologies drew inspiration from this microstructure to create a non-stick, ultra-repellent and self-healing surface coating.

Named SLIPS®, this liquid coating is applicable to a wide range of materials such as metals and ceramics, and repels all kinds of liquids and soiling particles. This provides unparalleled performance, especially compared to sprayed superhydrophobic surfaces.

In the automotive industry, such a coating opens up new avenues for solutions to reduce friction and improve the lubrication of systems.

Image credits: ©Adaptive Surface Technologies ©Bioxegy © I. Scholz, M. Bückins, L. Dolge, T. Erlinghagen, A. Weth, F. Hischen, J. Mayer, S. Hoffmann, M. Riederer, M. Riedel, W. Baumgartner

Snakes: reduce friction without lubrication to ensure good travel speed.

Snakes are crawling animals. To move quickly across all kinds of surfaces, they must manage friction in two ways: gripping for better propulsion and gliding to avoid drag. Their skin is made up of regularly spaced individual scales that reduce friction and wear.

Another remarkable reptile is the sandfish: it glides across the sand like a snake in water. It possesses a unique outer skin, whose resistance to erosion surpasses that of steel! Its skin is composed of keratin and sulfur, giving it an extremely low coefficient of friction.

Researchers at the Karlsruhe Institute of Technology in Germany studied the morphology of the skin and scales of these reptiles, enabling them to create bio-inspired metallic surfaces with unparalleled coefficients of friction. On dry surfaces, they discovered that this design resulted in a 40% reduction in friction compared to an equivalent, unmodified flat surface.

Exploring the potential of biomimicry to create surface textures is a relatively new and promising field of research. In many industries, such as watchmaking, such surface morphology could significantly reduce wear at the point of dry contact between two metal parts, for example, internal gears.

Image credits: ©Christian Greiner, Michael Schäfer

Fish skin : designing a revolutionary industrial lubricant

Fish have a gland that secretes a specific mucus which attaches to the skin and envelops the body.

Composed of mucoproteins, this mucus plays a crucial role: it allows the fish to protect itself against the penetration of pathogenic microorganisms, but also to move quickly in the water thanks to its very low coefficient of friction.

This mucus is also very effective in making the fish more elusive to predators: it slips.

A team of Chinese researchers sought to reproduce the properties of this powerful mucus. They succeeded in developing a hydrophilic substance called a hydrogel.

Containing specific chemical compounds, this material varies according to pH and temperature, which modify the molecular chains: conformational changes occur. The coefficient of friction is adjustable and can be very low or very high: At high pH (7) and room temperature (~20 °C), the coefficient of friction is very low: 0.05. At low pH and high temperature (32 °C), the coefficient of friction becomes very high: 1.2.

This bio-inspired lubricant with adjustable friction is particularly promising and could be used in many industrial mechanical components, across all sectors!

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Biomimicry, a promising toolbox in tribology