Bumps and Grooves Protect Surface

Biological Strategy

Desert scorpion

AskNature Team

Image: HTO /

Protect From Dirt/solids

When dirt and other small solids adhere to living systems, they can slow them down, create blockages, reduce their ability to carry out vital functions, or cause surface wear and tear. Due to electrostatic forces, it’s easy for dirt and other solids to adhere to surfaces, so living systems must overcome those forces. An earthworm, for example, uses a small electric current to keep soil particles from adhering to its body as it moves through the soil. This enables it to move more efficiently by reducing drag.

Search this Function

Manage Mechanical Wear

A living system is subject to mechanical wear when two parts rub against each other or when the living system comes in contact with abrasive components in its environment, such as sand or coral. Some abrasive components are a constant force, such as finger joints moving, while others occur infrequently, such as a sand storm moving across a desert. Living systems protect from mechanical wear using strategies appropriate to the level and frequency of the source, such as having abrasion-resistant surfaces, replaceable parts, or lubricants. For example, human joints like shoulders and knees move against each other all day, every day. To protect from mechanical wear, a lubricant reduces friction between the cartilage and the joint.

Search this Function

Arachnids

Class Arachnida (“spider”): Spiders, mites, ticks, scorpions

Arachnids get a bad reputation, but they play an important role in the ecosystem by controlling insect populations. Almost half of the species in the class are spiders, and most live in terrestrial environments. Unlike insects, most arachnids have two body sections: the cephalothorax, which is the head and thorax fused together, and the abdomen. Mites and ticks, on the other hand, have only one body section that is relatively flat. This body shape comes in handy for the species that are parasitic, because it makes it harder for their hosts to bite or scratch them off.

Search this Living System

The surface of the desert scorpion resists erosion by sand due to bumps and grooves that decrease flow.

A) Swirling air caught in the grooves creates air cushions and slow down the velocity of the wind. Airborne particles then either B) bounce away without impact or C) hit the surface at a much slower velocity and less impact. D) A particle hitting a flat surface where the wind does not diminish in velocity will have a much higher impact.

Desert scorpion (Androctonus australis) is a typical animal living in sandy deserts, and may face erosive action of blowing sand at a high speed. Based on the idea of bionics and biologic experimental techniques, the mechanisms of the sand erosion resistance of desert scorpion were investigated. Results showed that the desert scorpions used special microtextures such as bumps and grooves to construct the functional surfaces to achieve the erosion resistance…[studies showed that] the microtextured surfaces exhibited better erosion resistance than the smooth surfaces.” (Zhiwu et al. 2012:2914)

“Using gas flow analysis, the researchers showed that “the flow velocities are higher around the surface of the smooth sample than those of the convex surface and the grooved surface. Especially in the groove channel, the flow velocity was significantly lower than that of the smooth surface. It is shown that the flow path lines on the smooth surface were smooth. On the convex surface they were changed to a certain degree; it is indicated that the air flow was disturbed by the convex hull. But in the groove channel, the grooved surface has a great influence on the airflow. The air was rotating in the groove channel, forming a stable low-speed reverse flow zone.

“The special flow pattern in the groove has significant influence on the erosion resistance of the grooved sample. The rotating flow in the groove has an ‘air cushion’ effect. On one hand, the grooves can enhance fluid turbulence, which lead to change of the flow field around the groove surface, and the particle motion pattern was subsequently changed. Some of the particles will leave the surface along with air flow without impact, and these particles would impact the surface if the surface was smooth. Therefore, the number of particles impacting the surface was decreased. On the other hand, as a result of the decrease the [sic] flow velocity, the velocities of the particles in the two-phase flow were decreased as well. The rotating flow in the groove can absorb particle energy which was used for impacting, and the energy used in impact was correspondingly reduced. These features all help to reduce the particle impact damage on the sample surface and reduce erosion wear.” (Zhiwu et al. 2012:2917-2918)

Last Updated September 14, 2016

References

Journal article

Erosion Resistance of Bionic Functional Surfaces Inspired from Desert Scorpions

Langmuir | 30/12/2011 | Han Zhiwu, Zhang Junqiu, Ge Chao, Wen Li, Luquan Ren

embedly preview

AskNature