Frank Fish and his colleagues have published a paper on the aerial exuberance of the spinner dolphin (Stenella longirostris). This dolphin is named for their revolutionary ‘play’ where they spin as many as seven times as they leap into the air.  While airborne the dolphin waggles back and forth as well as spinning around.  It had been assumed that the wriggling motion was powering the spin as when a human high diver twists. Fish shows that this is simply not possible because the dolphin backbone is unwilling to do more than a back and forth motion.  This can’t be translated into rotational movement, instead the power comes from beneath the sea.  As the dolphin prepares to jump it begins a deceptively slow rotation. When the pectoral fins break the surface they no longer stabilize the body and the spinning begins.  All of the energy for spinning comes from the few tail beats before the jump.  They also show that the force of smacking back down is sufficient to dislodge remoras.

JEB abstract

In a previous entry I have pointed out the biophotonic possibilities in butterfly wings. A recent article in the Journal of Experimental Biology provides an extensive survey of wing scale optical properties. There had been no less than four different methods proposed by which butterfly wing scales could reflect colored light, this study found that only one method is at work.

The … analyses … of colour producing butterfly scales document that all species are appropriately nanostructured to produce visible colours by coherent scattering, i.e. differential interference and reinforcement of scattered, visible wavelengths.

They also found that the blue pigment of one Papilio species is not an incoherent Tyndal scattering phenomenon but rather the result of a fluorescent blue pigment. The take home message is that whether the nanostructuring is external or internal the method of filtering is the same.

JEB Abstract

I wrote a post on the sythesis of a bioengineered resilin a while ago.  This article is on the same research but is longer and more interesting than my post. 

The solid recombinant resilin features properties matching those of the natural version, Elvin says. The group is now working to better understand the material’s basic function so it can synthesize novel polymers that incorporate as building blocks the protein sequence responsible for elasticity.

Scientific American article

Speedo’s Fastskin suit cuts seconds off top swimmers times.  It is also an example of biomimicry in that the rough surface is supposed to be imimtating the tiny dermal denticles of sharks. The basic idea of the suit is that the little irregularities cause local micro-turbulence that decreases drag by allowing a quicker return to free stream velocity at a distance from the surface. 

I had thought that there was not very much experimental evidence that this system works, but I recently came across some really wonderful research on how the system functions. The suits are not very good mimics of sharks skin, but speedo has certainly commercialized a biomimetic product. More on the theory and experiments in a later post.

Random coverage

I am up in the air over whether this is biomimetic but it certainly is bioinspired. Mitchell Joachim of MITs Media lab leads a team that is designing a tree house. Not a house that will be put in a tree, but rather a living tree that will be sculpted into a house. Obviously a house that is also a tree will have radically innovative systems for all aspects of living. Water would be gathered in a roof-top trough and circulate by gravity through the house, where it would be used by the inhabitants, filtered through a garden, and purified in a pond containing bacteria, fish, and plants that consume organic waste. A composting system would treat human refuse. The main construction technique will be ‘pleaching’, weaving together growing branches to form various support and shelter structures. The only real drawback I see is that 10 years is the low end on an estimate for how long it will take to grow this house. Article

Starfish remain attached to irregularly shaped, slick surfaced rocks even while waves wash over them. This tenacity in a fluid environment should be of interest to biomimeticists, and has recently been quantified by biologists. Belgian researchers looked at the material properties and the adhesive capabilities of individual starfish tube feet.  Hundreds of the these hydrostatic structures propel the animal along and serve to hold it fast in the face of water drag.  The solution to the problem of sticking proves to be an interesting relief if you want to manufacture a wet attachment mechanism.

The tube foot is very compliant and over a relatively short time period will conform to the contours of even a rough substrate.  This leaves only a little room, the region of nanoscale roughness between surface and tube foot, that needs to be filled in with adhesive. The tube foot secretes this small amount of adhesive and is able to maintain the same attachment stress regardless of surface roughness.  Since a rough surface has more surface area than a smooth one the actual attachment force goes up on rough surfaces and only requires a very small amount of adhesive. This is welcome news if you want to build a mimic of this system as the adhesive delivery will be both complex and difficult to manufacture. The less of it needed the better. 

JEB Abstract

The adhesive qualities of the gecko foot rely on a nanoscale hairy spatula system that has been the subject of substantial biomimetic research. The upshot is that each spatula is so small and compliant that it can get very close to the substrate. So close that van der Waals weak forces become and important adhesive mechanism.  This is of interest to engineers because these adhesive forces do not require any adhesive fluid to be secreted, a boon for nano and microscale material handling. The attachment of the macroscale animal, whether it is a lizard, an insect or a spider relies on a huge number of these hairs.  For each critter the safety factor, the attachment strength above expected loading, is likely to be different. Antonia Kesel from Bremen has added to our general fund of information on these tiny spatulae by measuring single seta attachment force with an atomic force microscope (AFM) for the attachment structures of the jumping spider Evarchia. The tip of the AFM is allowed to come in contact with the seta and is then pulled away.  The deflection in the beam on which the tip rides is a measure of the attachment force.  These measures are notoriously difficult to obtain because the attachment force depends so heavily on local environmental conditions as well as the relative orientation of tip and spatula.  In this case the safety factor was calculated at 271 times body weight.  There are interesting scaling arguments for the effectiveness of this method of dry adhesion in Stas Gorb’s book.

Smart Materials Abstract

Cute ‘Spiderman’ popular press reporting of research

Secondary harmonic generation (SHG) is when the frequency of light that impinges on the surface of a material is doubled by some physical characteristic of the material.  The shifted light is emitted with a very different color than the input light.  These starch crystals from rice are showing SHG of incident red light.  The cool thing about this biomimetic generator is that the light can impinge over a wide range of angles.

Image info

An explanation of SHG

Face recognition software is complicated and expensive…perhaps some recent experimentation on bees offers insight into a simpler solution.  Bees have fewer than a million neurons and only a small subset are devoted to the tasks of visual patterns and memory. Yet Adrian Dyer in Mainz, Germany has managed to teach bees to recognize human faces.  The bees could distinguish between two faces they had been taught to love or hate and also could pick out a known face when faced with a choice between known and unknown.  This implies that there are some very simple biomimetic solutions to problems of machine vision and face recognition in particular. 

JEB article

A couple of Swedish researchers found that many animals have ‘multi-focal’ lenses in their eyes. These lenses are shaped so that different wavelengths of light are well focused on the retina. In association with these multi-focal lenes were slit shaped pupils. It turns out that a round pupil would block light from passing through some of the off axis focal centers. A slit pupil though allows all the foci access to incoming light allowing the animal to maintaina sharp, colorful image in both bright and dim light.

This is a strategy that I have not seen in conventional optics. Though a good deal of work goes into the manufacture of lenes with small chromatic aberation I have never seen a commercially produced multifocal lens. If such a lens exists it should have a slit shaped iris rather than a round one.

JEB Summary