Improvement of the human body through the application of technology is called ‘bionics’ in the US because of the popular ‘70s television show ‘The Bionic Man’. In Europe bionics is a synonym for biomimetic.  Though bionics as understood by Americans is perhaps not strictly within the purview of biomimetics it usually does require significant biomechanical understanding and so it is appropriate that I am interested in this type of research.

In a Wired Magazine article there is a report on two companies that are using portable adaptive optics to improve human vision.  In one case the adaptive optics are dynamically reconfigured as the environment changes. The wearer of these glasses would have better than 20/20 vision because the lenses would dynamically correct for large scale abberations in the anatomy of the eye. Apparently PixelOptics believes they will have a working prototype ready in one year.  A tall order.

A less ambitious plan by Opthonics takes a single mapping of the irregularities of a subjects eyes and produces a set of customized lenses that correct for that individual’s anatomical peculiarities. Though they do not correct to better than 20/20 these lenses are already available.

Wired Article

Andrei Peressadko and Stas Gorb have been looking at the question of adhesion in biological structures for some time.  In his book on attachment organs Gorb divided all sticky things into two classes – smooth and hairy.  Smooth adhesive organs use a combination of compliance and glue to stick, while hairy systems use zillions of tiny hairs to get close to the surface. In the paper linked below Peressadko shows an interesting phenomenon that can only be associated with hairy systems….the greater the subdivision of the surface (and hence lower area) the higher the attachment force.   Adhesion in of a smooth, soft  polymer block to a substrate was considerably lower than adhesion of the same block which had the surface chopped into smaller squares. This is really counterintuitive – the lower surface area had higher adhesive forces.  The oddity is due to the smaller chunks of polymer being able to follow the substrate more closely.

Abstract of Article

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

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

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

Micro sensors are a hot area of reasearch.  Most of the exciting work seems to be focussed on the Micro Electromechanical machines (MEMs). These tiny devices are sculpted by ion beams or other fab techniques out of silicon or corbon for models of much larger devices that are manufactured by traditional methods.  An area that should heat up is the stealing of sensor design from biological systems.  These designs are often already quite small and optimized for the nanoscale world of nerve transduction.  A case in point is the nanoscale flow sensors in teh lateral line of fishes. In the paper summarized below the authors measured the senstivity of neuromasts, tiny sensory devices located in pipes on the surface of some fishes, to very low velocity flow fields.  They confirm that arrays of neuromasts can measure the speed and direction of passing vortices of water.

Inside JEB article

One of the key inputs to biomimetic robot design is the kinematics of the biological system being imitated.  There are several different ‘gecko’ robots that currently imitate the lizard by spinning various configurations of a sticky tire to climb walls.  The biomimetic models are united in their treatment of walls and floor in the same way.  This paper shows that the geckos are not so limited.  When running up walls they use a fundamentally different gait in which the legs are pulled into the body to set the clinging hairs (setae) into the surface.  On the ground they use a superficially similar gait but the forces on the feet push out rather than in on impact.  This important difference needs to be realized in the next generation of gecko-bots. 

Inside JEB article

Microfluidics is concerned with pumping and valving nanoliter volumes of liquids. There are many non-biological approaches but there are also some potentially interesting biomimetic approaches. A discovery phase project involves understanding the seemingly simple transport of water up a tree.  The pipes (xylem) in which water flows do not run the length of the tree.  Xylem cells connect, one with another through pits along their length. In the event that an air embolism appears in one xylem tube it cannot travel to another because each pit has a tiny backflow preventer valve.  When there is a pressure difference between adjacent cells the preventer flops across the pit and stops air from crossing intot he next cell.

Cool images

Some animals, like mammals and birds, maintain a constant, relatively high body temperature while others, fish and reptiles for instance, allow their body temperature to vary quite a lot. There are some hot-blooded exceptions, fish like tunas and white sharks, maintain a constant, high body temperature in certain parts of their body. An advantage of our (mammalian) strategy of temperature regulation is that evolution can optimize proteins for a particular temperature. Rather than having to work pretty well at a wide range of body temperatures mammal and bird muscle works REALLY well at 37 degrees Centigrade and not well at other temperatures. This optimization has now been shown to apply to endothermic sharks as well.

The salmon shark (Lamna ditropis) swims in the fridgid waters of the arctic yet it maintains a core body temperature well above ambient. Diego Bernal and several colleagues have demonstrated that the contractile properties of the muscle from the warm regions of this shark respond to temperature like mammalian muscle. Function is greatly impaired by changes in temperature. There are two important implications here. Firstly, the exact solution that allows muscle to maximize performance at a single, high temperature has evolved more than once. This is an excellent opportunity to look at the fine details of the evolution of a complex biochemical system. Second, the narrow range of activity for the cruising muscles of Lamna tells us, with greater certainty than the few thermo tag results, that the core temperature of the animal is truly invariant. This second factor may play a role in the distribution and habits of the lamnid sharks (salmon, white, mako and porbeagle).