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Living, breathing biomimetic meta materials
12 September 2016 | David Bradley
An intriguing video has been doing the rounds (since 2015) in the science-oriented corners of social media for a while. You may well have seen it, it shows a "material" being squashed between two Petri dish halves and bouncing back to its original shape, of being picked up and dropped and landing with a silent energy-damped thud. It's weird, what is this stuff, some new kind of non-Newtonian polymer blend to rival Silly Putty or one of those other great technological advances of the latter part of the twentieth century?
No. A closer look reveals that some of the "molecules" are so big that they're visible to the camera eye and crawling around the edges of the blob of material. An even closer look reveals that these molecules have six legs and biting mouth parts. In fact, they are not molecules at all, they are fire ants; fire ants clinging to each other and behaving in concert, responding to the stresses and strains to which the mass of ants is subjected.
Now, we have known for a long time that ants are social creatures and work together to build a nest, bring food to that nest, grow their own food in the form of subterranean fluorescent fungi, serve their queen, act as guards against intruders like a kind of immune system for the nest. But, this clingy behavior that makes them resemble a mobile meta material is quite astounding. It got me thinking, there are several chains of thought in materials research.
For instance, some scientists and technologists track biology and develop biomimetic materials with startlingly natural properties for a wide range of applications. Those materials are generally not dynamic, they don't behave like the fire ant meta-organism, although various shape-shifting gels and their ilk have been created that respond to environmental change. In parallel with biomimicry there are those researchers working on composites and meta materials, systems that perhaps combine macro-, micro-, or nano-scopic components to generate properties and characteristics that are beyond the behavior of conventional materials and those we see in nature, perhaps the most famous are the "invisibility", or cloaking, meta materials that have clamored for attention in the mainstream pop sci press in recent years.
My thought, then on seeing the fire ant meta organism-material was that perhaps we could devise an entirely new type of supra-meta-material. Materials based not on macromolecules, whether synthetic polymers, proteins, or nucleic acids, but where the components are individual organisms that work together to endow the collective with unique non-classical properties. It did occur to me that science fiction is a little ahead of me on this idea, particularly with the nanobot swarms in Michael Crichton's 2002 novel Prey and the "healing" nanobots of the 2005 Doctor Who episode The Empty Child. There are no doubt other examples.
A living technology, organisms (engineered, modified and augmented) working dynamically in self-repairing structures that can be used in a range of applications vehicle and aircraft safety, building foundations that are resistant to seismic shock, heating and cooling systems, power generation. I am sure those with greater imagination than I can think of examples of where a responsive and adaptive system, a synthetic ecosystem, a bio meta material might be useful. I then realized on writing this last paragraph that such systems already exist not just in the self-protecting blobs of fire ants but in the form of slime moulds and certain seaweeds in which single cell creatures coordinate their structures and properties to work together to solve their individual problems of nutrition, reproduction and waste disposal as a collective. There are probably many other examples. Perhaps the meta materials scientists and the biomimetic teams should get together. The whole is often greater than the sum of the parts, after all.
David Bradley blogs at Sciencebase Science Blog and tweets @sciencebase, he is author of the popular science book "Deceived Wisdom".
The studies on fire ant solid-liquid collective behavior was carried out by David Hu and his team at Georgia Tech, part of the phenomenon is related to the ants creating waterproof rafts by hitching themselves together. They have also investigated how hairiness keeps animals clean and many other fascinating aspects of what one might picture as the meta world of living things.
http://www.news.gatech.edu/2015/10/26/ants-both-solid-and-liquid
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