Problem-solving biomimicry

Materials World magazine
,
1 Sep 2018

Flat bark bugs, lizards, camels and tide pools have inspired the latest research in mimicking nature, bringing this problem-solving into engineering and medicine. Ines Nastali reports.

Take a look around – for many of our engineering and design problems, we can see that nature has already provided a solution, or is at least pointing the way. A recently concluded EU project, Laser-Induced Nanostructures as Biomimetic Model of Fluid Transport in the Integument of Animals, summarised in the handy abbreviation LiNaBioFluid, looked at ‘laser-fabrication of biomimetic surfaces with unique wetting properties, inspired by the hierarchical micro and nano-structures of the integument of animals’, in order to reduce friction and wear in lubricants, to steer fluids better and, therefore, make machines more efficient, the researchers involved state on the project website. 

Efforts were aimed at a variety of applications, including slide bearings in combustion engines – which the researchers claim they have achieved a 90% friction reduction, ultimately achieving a CO2 reduction – needles used for drug delivery through the skin, and wound dressings that can drain fluids away from wounds in a controlled manner. 

These are some of the many examples of researchers copying nature’s clever solutions in order to solve mankind’s engineering problems, known as biomimicry. 

A bug’s life 

The LiNaBioFluid researchers wanting to improve the lubrication process used electron microscopes to study how lizards living in arid conditions collect dew through their skin and how flat bark bugs’ skin changes colour when they are wet.

They discovered that the animals make use of the principle that, at the micro scale, rough surfaces have less friction than smooth ones. While the principle was already known, researchers wanted to expand their previously limited scientific knowledge about the flat bark bug in general. 

‘The fluid transport on the cuticle of some bark bugs includes the transport of the fluid out of the capillary, followed by the spreading of the fluid on an extended area with microstructures. This special kind of fluid transport is assumed to be caused by the specific microstructures and wettability of the bark bug cuticle,’ the researchers state. 

While the bugs transport moisture from a system of capillaries to a wider area on their body, lizards do the opposite by collecting water from a plain area to be fed into the capillary network. Therefore, the scientists also took high-resolution images of the animals’ skin surfaces to further examine the structures that produce these properties. ‘Finally, these structures were duplicated using advanced laser technology on hard, inorganic materials like silicon, steel, bronze and titanium alloys,’ they said.

They opted for laser technology as ‘it is not feasible to mimic the surface structure of the bark bug cuticle or the scale of a moisture harvesting lizard on a larger surface of several square centimetres by a scribing technique such as electron beam lithography due to the long processing times required’, they state. ‘Therefore, we employed the self-organised structures occurring on laser irradiated surfaces for structuring of surfaces on technically relevant hard materials, which show many similarities to those found in the animal integuments.’

Mimicking design

Harvesting the knowledge that camels, just like the lizards, collect morning dew, students from California State University, USA, developed a building insulation grid that can be retrofitted to the outside of existing buildings. The aim being to reduce the building’s temperature without using electricity. 

This Phalanx insulation derived from the camel’s nasal cavity structure, which creates turbulence, and the interior nose walls that absorb moisture. Similar techniques to cool down are used by termites and even wheat.

The insulation consists of three layers and would be mounted on top of the outside wall. The first layer is honeycomb inspired and traps the heat from the sun, the air that comes with the heat rises up into the second, capillary layer, when it heats up, and through surface tension, water is absorbed and evaporates, which absorbs heat again and thereby cools the house wall. 

Phalanx insulation was one of eight winners of the Biomimicry Global Design Challenge 2018, which were announced at the end of June. The challenge is organised by the Biomimicry Institute based in the USA, which also curated an online database AskNature of nature inspired solutions to protect buildings from fractures or floods, and to help designers to learn from nature when planning future projects. 

The concrete pool

Another winner of the design challenge was the team that developed ECOncrete. They managed to mimic natural tide pools and rocky shores to attract marine growth that has been robbed of its habitat by coastal defence systems. 

The company’s tide pools are made of concrete, containing ground granulated blast-furnace slag (GGB) and Portland cement. Around 10% of this concrete has been replaced with quarry by-products that would have otherwise been disposed of. ‘We have identified quarries around the world that have a certain geological layer, which is useful to us,’ Ido Sella, Marine Ecologist and Co-founder of ECOncrete, told Materials World. Particles of around 40μm then get added to the cement mix and shipped to customers. 

‘Concrete only attracts specific species, which are known to be robust and often invasive,’ Sella said. With the tide pools, enhanced sea walls or concrete mattresses employed in coastal areas, the company was able to ‘reduce the amount of alien and increase the amount of local species,’ he said, adding that they found that their concrete also offers better freeze protection than common Portland cement-based alternatives. 

In addition, less greenhouse gas is emitted during production, the company claims. ‘When slag cement replaces 50% of the Portland cement, greenhouse gas emissions per cubic yard of concrete are reduced by 45%. For example, while an average of 931kg of CO2 are emitted for every 1,000kg of ordinary Portland cement, GGB emits 26.5kg.’ With an increased amount of marine life settled – such as oysters, coralline algae, tube worms or barnacles – anthropogenic CO2 emissions can be reduced as the oceans and the life within act as a carbon sink. 

This project also shows, nature can provide structural engineering protection. ‘Be it oysters and corals that physically protect the concrete from scour and chloride attacks, or plant canopy capable of buffering temperature changes and the humidity level on the concrete surface.'