In many conifers the pine cone on the tree has its scales tightly closed protecting the seeds that lie inside. When the cone falls off the tree and starts to dry out the scales open up, scattering the seeds.  The forces that drive the opening movement are fibers running at 90 degrees to one another on the inner and outer surface of the scale.  As the scale dries the fibers shorten and cause the scale to flex towards the stem of the cone. 

Julian Vincent, the biomimetics doyen of Bath, has teamed up with clothing manufactures to produce cloth that works on the pine cone principle. They envision tiny hairs on the outer layer of the fabric that will stay closed when the wearer is not sweating and needs protection from the wind, but will open up to allow a breeze through when the wearer starts to sweat.

 The projec tis being undertaken by Veronika Kapsali, at the London College of Fashion. She says:  

It’s been great fun working on a project that is going to lead to a fundamental change in clothing

Bath Press Release

 James McLurkin, a graduate student at MIT, is engaged in what I believe is the most profitable form of biomimetics - stealing ideas about behavior. Ants search aimlessly for food, yet after they have found it and returned (via the aimless path that brought them) to the nest, susequent workers shorten the path over successive trip until it is as direct as can be given the terrain.  The best thing is that they optimize on time which takes into account the difficulty of various routes, rather than purely on distance. 

The method the ants use is a simple byproduct of the nature of their trailing behavior.  They follow scent trails and any randomly derived trail that is a little shorter than the parent trail will smell stronger to the next ant along because there has been less time for the scent to evaporate. It is a slowly evolving solution, but it ends up near optimality without trying all possible combinations.

McLurkin builds small, autonomous robots that interact with one another in the same way ants and bees do - simpleminded exchanges of very basic information. From this basic beginning he has a start on some seriously useful robotics. The project is aimed at imbuing swarms of tiny (even nanoscale) robots with a set of useful behaviors. 

MIT Homepage

Lemelson Student Prize notice

Julian Vincent and his crew at Bath have used the ovipositor of the wood wasp as a model for a new sort of drill they suppose might be of use in low gravity situations.

We worked out how a wood wasp drill works, and then tried to make a machine out of it. One side pushes in and cuts, and the other side is pulling itself out and gathering the sawdust and taking it up to the top. In a way it is a paradigm of biomimetics. We allowed the wasp to do nearly all our work. Now we have a pretty good prototype first time round, courtesy of nature

Alex Ellery at Surrey, a space roboticist, explains that the ovipositor of the wasp is a tube split in half. The wasp bores by alternately sliding the two halves past one another. Rasp-like teeth on the outside of the tube do double duty, alternately holding fast in the wood, then cutting and carrying the sawdust out of the hole.  Since these teeth provide the purchase for drilling there is no need for gravity. 

PDF on space robot drill

BBC article

If you are interested in keeping ahead of the biomimetics field it is a good idea to be notified when Julian Vincent publishes a new article. His book on biomaterials is the classic in the field, and as the head of the University of Bath’s Center for Biomimetics and Natural Technologies he is on the forefront of current biomimetics research. One of his research projects that is getting quite a bit of current press is on clothing that mimics pine cones in order to shed internally generated moisture.  I’ll write about that in a future entry.

In a Wired article on a Nature article it is reported that researchers at UCSF have spliced light sensitive genes into bacteria. Dishes of the little darlings can then be exposed to light, in this case images of the researchers.  There is no need to develop the images because the light sensitive genes, stolen from algae, produce a dark material on exposure to light.  The article says this is an example of ’synthetic biology’ but it seems in the spirit of biomimetics.  By understanding the function of the algal genes the researchers were able to co-opt the in vivo system to another purpose.

Wired Article

Nature Article (subscription required)

No animal with a high metabolic rate can extract enough oxygen from water to survive. That is the fundamental problem with the artificial gill.  Let us suppose a system could be disigned that would extract a normal human’s oxygen needs from seawater. Ignore for a moment the issues of volume changes imposed by pressure at depth.  Ignore also that oxygen must be delivered mixed with some other gas because it is toxic in high concentrations. Consider a person floating at the surface with the needed oxygen supplied by this machine and the extra gas somehow recycled so it need not be regenerated. 

The resting metabolic rate (energy output) of this relaxed person is about 8 megajoules  or 2000 kilocalories per day.  It takes about 1 liter of oxygen to aerobically produce 20 Kilojoules of energy, or 400 liters of oxygen per day to stay alive.  No problem to obtain this from air since air is about 20% oxygen  - this translates to a pretty trivial 2000 liters of air per day.  Converting liters to moles so we can easily work in both dissolved and gas phase we get that 400 liters of oxygen is about 18 moles of the gas.

The problem lies in the amount of oxygen that will ‘fit’ into a liter of water.  Gasses dissolve in water in different amounts depending on the both the gas and the temperature of the water. Carbon dioxide for example is happy to dissolve in water and 390 micromols will dissolve in a liter at room temperature per kilopascal of pressure.  Carbon dioxide is about 30 times more soluble than oxygen so just 14 micromols will dissolve in a liter of water under the same conditions. So far I will admit that this excercise has been no fun, but you need to hang on for a few more steps…it really is better than believing in a biomimetic gill to support a diver.

Assume the oxygen in the water is in equilibrium with the air, that is, there is as much oxygen in the water as will fit given the temperature and oxygen content of air.  The pressure of air at the surface of the water is about 100 kPA and about 20% of the pressure is due to oxygen.  That means 20 kPa of pressure is due to oxygen and for every kilopascal, about 14 micromols of oxygen will dissolve.  OK, that is a grand total of nearly 300 micromols of oxygen.  Recall that to stay alive at rest a human uses 18 moles of oxygen - if it were possilbe to completely remove the dissovled oxygen this would be the amount found in 60,000 liters of water. 

Sixty thousand liters of water per day, 2500 liters per hour, 41 liters per minute, or 0.7 liters per second.  No matter how you look at it this is a  large amount of water.  Quite apart from the problematic assumption of complete extraction, moving this much water will engender a huge reaction force. The thrust generated by the gill system just by moving the water will be quite substantial.  This is simply impractical. It can’t work for humans.

How then does it work for fish?  Most fish have very low metabolic rates, they conform to the environmental temperature.  Tunas are among the few fish that do have some regional body warmth, and they have most elaborate gills and easily suffocate if prevented from ram ventilating at high speed .

Are artificial gills a total boondoggle?  Not at all, there are numerous sensible applications for a device that can transfer gas from one fluid to another with high efficiency.  But the motivation for building these devices simply can’t be as a replacement for SCUBA.

The research team at Waseda University in Japan led by Fukashi Kohori is working on REALLY imitating the oxygen transport system in an artificial gill.  Rather than using an organic compound with a high oxygen affinity Kohori proposes to use the same carrier as is found in vertebrate blood - hemoglobin.  He has written a description of the design parameters for an artificial gill that could support a human underwater. As in all models of this sort there is a problem moving from theory to reality because of a mismatch between the physics of water and the physiology of humans. 

Kohori’s more plausible research is a biomimetic kidney.

Another take on the biomimetic gill - in previous posts I have talked about the biomimetic oxygen carrying fluid and a solution to gas extraction that bypasses both the structural complexity of the gill and the need for transporting gas in a liquid carrier. An alternative approach to the Israeli extraction technique is to combine the oxygen transport fluid with an imitation of the structural complexity of the gill.  Here is an STTR phase I project that plans just that.

Infoscitex and Case Western Reserve University propose the development of a biomimetic synthetic gill design based on the subdividing regions of clef, filament, and lamellae found in natural fish gills.  

This project is aimed squarely at the most technically demanding aspect of this biomimetic process as they will have to perform microfabrication with a material that resists fouling and passes fluid easily.  No small task.  Still unaddressed is the fundamental physiological problem of creating an artificial gill to support humans underwater.

Article

We have previously mentioned cases where a man-made solution to a problem is later discovered to use a similar approach to what is found in nature. Here is another example.

The BBC picks up on one of the articles in the current issue of Science that I mentioned below. The article highlights the research of Peter Vukusic and Ian Hooper at the University of Exeter who determined that the wing scales of African swallow tail butterflies (and keep your Monty Python references to yourselves) bear a striking resemblance to two dimensional photonic crystals used in the creation of high-efficiency LEDs.

Like its counterpart in a high emission LED, it prevents the fluorescent colour from being trapped inside the structure and from being emitted sideways.

The scales also have a type of mirror underneath them to upwardly reflect all the fluorescent light that gets emitted down towards it. Again, this is very similar to the Bragg reflectors in high emission LEDs.

“Unlike the diodes, the butterfly’s system clearly doesn’t have semiconductor in it and it doesn’t produce its own radiative energy,” Dr Vukusic told the BBC News website “That makes it doubly efficient in a way.

“But the way light is extracted from the butterfly’s system is more than an analogy - it’s all but identical in design to the LED.”

The current issue of Science (subscription required) focuses on biomimetics:

When a child sees a bird flying past or the fluttering wings of a butterfly, does it inspire thoughts about how to build airplanes? Or does it simply convey the idea that flight is possible? We are immersed in the natural world, so it is not surprising that it inspires the design of engineered structures, or that we would like to probe this world further to learn all its secrets.

The four Reviews in this issue highlight this two-sided relationship as it applies to the development of new materials. From nature we have learned how soft brittle materials like chalk are made tougher through composite structures. Some of these same design principles have been applied to the much wider range of building blocks available to the engineer (Mayer, p. 1144). Advances in materials processing, particularly in the area of polymers, are also making it possible to fabricate systems with advanced optical capabilities (Lee and Szema, p. 1148), inspired by living eyes and by creatures that we have recently learned can see even though they appear to lack eyes.