Wednesday, March 12, 2014

Learn Engineering from Nature

Surface Structure of a Springtail
Christian Thaulow, NTNU, Norway 

Biomimetics is the imitation of the models, systems, and elements of nature for the purpose of solving complex human problems. The terms biomimicry and biomimetics come from the Greek words bios, meaning life, and mimesis, meaning to imitate. A closely related field is bionics.

Over the last 3.6 billion years, nature has gone through a process of trial and error to refine the living organisms, processes, and materials on Earth. The emerging field of biomimetics has given rise to new technologies created from biologically inspired engineering at both the macro scale and nanoscale levels. Biomimetics is not a new idea. Humans have been looking at nature for answers to both complex and simple problems throughout our existence. Nature has solved many of today's engineering problems such as self-healing abilities, environmental exposure tolerance and resistance, hydrophobicity, self-assembly, and harnessing solar energy through the evolutionary mechanics of selective advantages.

No, this isn't something out of horror movie. These are the gears - a remarkable feat of "organic engineering" - of aIssus coleaptratus nymph (photo courtesy of The University of Cambridge).

Nature turns out to be as prodigious an engineer as human beings. The University of Cambridge recently discovered that a European plant-hopping insect called the Issus coleaptratus possesses natural, biological gears not unlike those found in bicycles, transmissions, and automobile differentials. Adding to the surprise of this discovery, the Issus has been living comfortably in European gardens for decades. Only ornamental “gears” have been spotted in nature prior to this discovery; those of the Issus, however, play an essential role in the insect’s survival.

This is a micrograph of a rainbow butterfly's microstructure. The arrangement of the grooves gives rise to a dull blue color that can be observed with the naked eye.

There are many displays of iridescence in nature, found in many different climates, for presumably, many different reasons. Iridescence is simply coloration due to a microscopic physical geometry, rather than the pigments that are usually considered to be sources of coloration. The wings of Blue Morpho butterfly,the Urania ripheus butterfly, the Rainboy Butterfly, and the surface of the mother of pearl, sea shell, all share a similar mode of coloration: iridescence. The apparent bend of the light comes from interference caused by small surface grooves on the surface. There are approximately 4 striations on one micrometer of Blue Morpho wing, and they are supposed to be made of chitin, the same material marine creature's shells are made of. Looking at objects of this size is well within the magnification range of the microscope.

Scanning electron microscope image of the eye on a leaf miner moth. 
(Image:Dartmouth College)

Using the compound eyes of the humble moth as their inspiration, an international team of physicists from the City University of New York and Tongji University in Shanghai applied biomimicry to develop new nanoscale materials that could someday increase the resolution of the resulting X-ray images without the need for larger radiation dosages which occur due to amplification of input radiation.

Moths have large compound eyes which consist out of many thousands of ommatidia-structures which form a primitive cornea and lens that are connected to photoreceptor cells. Their eyes are also anti-reflective and bounce back very little of the light that strikes them in order to help the insects be stealthier and less visible to predators during their nocturnal flights. Because of this feature, engineers have looked to the moth eye to help design more efficient coatings for solar panels and displays.

Led by Yasha Yi, a professor of the City University of New York, who is also affiliated with MIT and New York University, the researchers took another path and used the moth eye as a model for a new class of materials that improve the light-capturing efficiency of X-ray machines and similar medical imaging devices.

Glass spheres among microhairs that are mushroom-shaped to improve adhesive force. 
(SEM: Michael Röhrig, KIT)

Geckos outclass adhesive tapes in one respect: Even after repeated contact with dirt and dust do their feet perfectly adhere to smooth surfaces. Researchers of the KIT and the Carnegie Mellon University, Pittsburgh, have now developed the first adhesive tape that does not only adhere to a surface as reliably as the toes of a gecko, but also possesses similar self-cleaning properties. Using such a tape, food packagings or bandages might be opened and closed several times.

Through the study of nanobiomimicry, key components of nanodevices like nanowires, quantum dots, and nanotubes have been produced in an efficient and simple manner when compared to more conventional lithographic techniques. Many of these biologically derived structures are then developed into applications for photovoltaics, sensors, filtration, insulation, and medical uses. The field of nanobiomimetics is highly multidisciplinary, and requires collaboration between biologists, engineers, physicists, material scientists, nanotechnologists and other related fields. In the past century, the growing field of nanotechnology has produced several novel materials and enabled scientists to produce nanoscale biological replicas.