There is considerable interest in the manufacture of nanoscale submersible vehicles. The biological world is rife with them, from sperm to ciliates, but until now their manufacture has been impossible. A team of researchers from France have added a magnetic tail to human red blood cells and caused them to ‘swim’ in an oscillating magnetic field. The tail is a strand of DNA with a built in affinity for tiny magnetic spheres. When the DNA strand is attached to the blood cell and the field is turned on the cell swims in the opposite direction of a sperm - tail first. The really cool thing about this research is that we now have a platform for testing different nanoscale swimming strategies and morphologies.

The eight arms of the octopus are a roboticists wet-dream and nightmare all at once. Being able to control so many different, flexible manipulators would be a true boon for a robot, but the difficulty of controlling arms without joints is a computational nightmare. It may turn out not to be so very difficult. A team in Israel has made a 2 dimensional computer model in which a simple pulse of contractile activity in both the longitudinal and circumferential muscles passes along the arm. The arm will bend and the bend travels down the arm much as it does in a live animal. Perhaps soft manipulators will not be as difficult to control as had been thought.

Here is a link to a very cool article about a fellow who has the software for his hearing implant hacked so he can better hear Bolero. The article uses the term ‘bionic’ which has historically meant machine man interfaced devices, but in Europe is used as a synonym of biomimetics. I have not yet decided how we will use it here in the blog, but I will post a definition of bionic when I do.

One of the clearest examples of taking a biomimetic product to market is that of the ‘Lotus Effect‘ products. The basic principle as well as the fine details of design are based on the way that water rolls off the leaves of the lotus plant (Nelumbo nucifera). Pay attention to the time line, it is probably as good as it gets for moving biological understanding to commercial realization.

In the 1970’s Wilhelm Barthlott, now at the University of Bonn, Germany, noticed the dirt resistant properties of certain plant leaves. If you stop and think a moment, in spite of living in a dirt filled world, indeed, with their very roots in soil, plants seldom have much noticeable grime on their surfaces. This is a good thing since it would undoubtedly interfere with photosynthesis. This lack of dirt is not due to paucity of local grime but rather to the ease with which any water that hits the leaf washes away offending particles.

Dirt washes away because the surface of the some leaves, and the sacred lotus in particular, are very resistant to ‘wetting’. Wetting refers to the ability of a liquid droplet to spread out on a surface and depends on the properties of the substrate and the liquid. Wettability can be quantified by measuring the contact angle that a droplet forms with a surface. On a water wettable surface, say untreated wood, a droplet will lay out nearly flat with a very low contact angle. The same droplet on a newly waxed table stays drop-like and has a high contact angle. When water hits a wettable surface any dirt on the surface is jostled around then settles back on the surface. On the other hand when water hits an unwettable or hydrophobic surface the dirt becomes suspended in the water droplet and can’t get back to the surface. As the drop rolls it carries dirt with it.

Obviously this is not a completely novel idea. The reason we wax out cars is not that wax is a bullet-proof, scuff resistant coating, but rather that it makes it easier to wash dirt off and harder for dirt to stick. The secret to the lotus plant’s dirt busting is a bit more complicated than just wax, but wax is at the root of the solution. The leaves of the lotus are covered with a waxy secretion that repels water. The surface geometry of the wax further repels water. Tiny mounds of wax, on the micron size scale, serve to hold surface drops of water up above the leaf, increasing contact angle beyond that found on an unpatterned wax surface.

Barthlott patented the pattern of bumps in the hydrophobic surface and called it the Lotus Effect ™. The German paint company STO has introduced a paint with emulsified waxes that dries into a micro rough surface. This paint, Lotusan, will stay clean as long as there are regular applications of water. It is really only suitable for exterior use, but in that capacity it now has a 4 year track record. Of course the surface is subject to attack by the elements and I suspect that the oilier the local dirt the hard it is for Lotusan to stay clean. In fact, if Lotusan does get dirty it is problematic to clean it since rubbing it disturbs the micro-patterned surface ruining the self-cleaning properties.

Further products in late development or early commercialization are self cleaning roof tiles and a sprayable self cleaning coating.

I am a comparative biomechanic and my training relied heavily on the books by Steve Vogel and his colleague Steve Wainwright at Duke University. They helped to train a generation of my colleagues with now classic volumes like Life in Moving Fluids, Axis and Circumference, Life’s Devices and Mechanical Design in Organisms. The field has moved considerably since the publication of these volumes so it’s great to see a new and heavily updated volume from Vogel.

Comparative Biomechanics - Life’s Physical World
will serve a number of purposes over the next several years. For one, it is a well written, approachable primer to the interaction of biological problems and physics/engineering. Engineers and physicists need readable introductions to the complexity of biological design and this book does a reasonable, though not in depth, job of pointing out the myriad biological systems to which interesting math can be applied. Biologists in their turn need usefully written mathematically oriented tracts in order to understand the predictive power of the physical sciences. Since most biologists are not comfortable with post-pre-calculus mathematics the tone and clarity of this book will be a great bridge into the useful fields of fluid mechanics, elastics and dynamics, heat transfer and flow.

The book must have started as an updating of Life’s Devices, but somewhere along the way a complete rewrite of Life in Moving Fluids ended up forming the beginning of the book. There is great material on both solids and fluids, but by far the strongest work is in fluids. In part this is because there are so many equations in fluid mechanics that have application to biology (we are after all quite wet), these equations are in dire need of a clear explanation. From Bernoulli to Navier-Stokes, Vogel does an excellent job of walking the reader through both the derivation and the relevance. The explanations and derivations stay with the reader far longer than would be expected for heavy material of this sort.

This book is a great place to start when you are wondering what is known about the biomechanics of subject X, but it is also fascinating reading as a biological exploration.

Stanislas Gorb, of the Max Planck Institute in Stuttgart, has written a bookabout attachment mechanisms of insects. Though murderously expensive new ($145) since ‘dry’ adhesives are one of the hottest topics in nanobio and biomimetics this book does have a market. The savvy lay person could certainly learn enough from Gorb’s easygoing style to tease fact from hype in press coverage of the issue.

If you are looking for a really good in depth treatment of the phenomena of friction and attachment as they relate to surfaces and biological materials this is a great place to start. The material is a competent survey of the primary literature in the field and presents little new data not published elsewhere. On the other hand it does a fantastic job of summing up groups of papers that are difficult for the lay person to approach.

The introductory chapters explain the physical phenomena involved in attachment, and they are general enough topics that they nicely explain gecko adhesion as well. The book goes on to divide attachment strategies into either ‘hairy’ or ’smooth’. The former relies on large numbers of flexible projections to maximize realized contact area with a substrate. In contrast, ’smooth’ attachments rely on viscoelastic deformation of the attachment surface to flow into the nooks and crannies of irregular surfaces.

Among the most interesting topics covered in the book is one on the scaling of attachment force. Gorb reviews the literature for insects, spider and lizards and shows that there is a clear relationship between the amount of force required to support the animal and the number and width of the tiny hairs on the foot (or toe) pad. For those who are interested in the commercial possibilities of ‘dry’ adhesives this provides a clear link between the stickiness and the surface complexity (and hence cost) of possible biomimetic materials.

There are also very nice sections in the book that deal with the interaction between insects and the plants they walk on. This area of research is a hot topic because the nature of plant surfaces is such that they can be hard for insects to hang on to.

A beetle found in the Namib Desert stands tail high in the cool morning fog to drink the water that collects on its own back and drips into its mouth. English scientists mimicked the pattern of hydrophilic and hydrophobic surfaces they found on the beetles back to make small scale solid panel fog collectors

. Though the samples tested were just glass microscope slides, the concept seems that it might be easily scaled up to larger scale fog collection devices. Though fog collection has been installed in some remote areas to provide drinking and irrigation water, the current technology (nets on tubing) requires too much maintenance.

A form or mechanical function rooted in a design concept found in nature. An example of bioinspired design is the slippery shape of the new Mercedes Benz concept car. Typically products characterized as bioinspired design are close to commercialization or are already commercialized.

When Mercedes Benz engineers sat down to design the next generation concept car they drew their inspiration from the Yellow Boxfish (Ostracion cubicus). Despite its boxy shape, the boxfish has a drag coefficient nearly as low as a drop of water — the theoretical ideal. The low drag, combined with a thrifty 1.9 liter turbo-diesel engine, means you get 84 mpg while cruising at 56 miles per hour. Article

Fly feet end in tiny spatulas that conform to any surface they touch allowing the fly to adhere with unexpectedly high force. With an atomic force microscope to measure the adhesive properties of the little wet footprints they leave behind, it is clear that a good deal of this adhesive capability is due to capilary action between the surface and the seta. This means that a man-made adhesive based on the setae would have to be lubricated in some way. Since lubricants often attract dirt this requirement is not a welcome addition to our understanding of fibrous adhesion systems.