Ways that nat­u­ral nan­otech­nol­ogy could in­spire hu­man de­sign

Tehran Times - - TECHNOLOGY -

Though nan­otech­nol­ogy is por­trayed as a fairly re­cent hu­man in­ven­tion, na­ture is ac­tu­ally full of nanoscopic ar­chi­tec­tures. They un­der­pin the es­sen­tial func­tions of a va­ri­ety of life forms, from bac­te­ria to ber­ries, wasps to whales.

In fact, tact­ful use of the prin­ci­ples of nanoscience can be traced to nat­u­ral struc­tures that are over 500m-year­sold. Be­low are just five sources of in­spi­ra­tion that sci­en­tists could use to cre­ate the next gen­er­a­tion of hu­man tech­nol­ogy.

Struc­tural col­ors

The col­oration of sev­eral types of bee­tles and but­ter­flies is pro­duced by sets of care­fully spaced nanoscopic pil­lars. Made of sug­ars such as chi­tosan, or pro­teins like ker­atin, the widths of slits be­tween the pil­lars are en­gi­neered to ma­nip­u­late light to achieve cer­tain colours or ef­fects like iri­des­cence. One ben­e­fit of this strat­egy is re­silience. Pig­ments tend to bleach with ex­po­sure to light, but struc­tural colours are sta­ble for re­mark­ably long pe­ri­ods. A re­cent study of struc­tural col­oration in metal­lic-blue mar­ble ber­ries, for ex­am­ple, fea­tured spec­i­mens col­lected in 1974, which had main­tained their color de­spite be­ing long dead.

An­other ad­van­tage is that color can be changed by sim­ply vary­ing the size and shape of the slits, and by fill­ing the pores with liq­uids or va­pors too. In fact, of­ten the first clue to the pres­ence of struc­tural col­oration is a vivid color change af­ter the spec­i­men has been soaked in wa­ter. Some wing struc­tures are so sen­si­tive to air den­sity in the slits that color changes are seen in re­sponse to tem­per­a­ture too.

Long range vis­i­bil­ity

In ad­di­tion to sim­ply de­flect­ing light at an an­gle to achieve the ap­pear­ance of color, some ul­tra-thin lay­ers of slit pan­els com­pletely re­verse the di­rec­tion of the travel of light rays. This de­flec­tion and block­ing of light can work to­gether to cre­ate stun­ning op­ti­cal ef­fects such as a sin­gle but­ter­fly’s wings with half-a-mile vis­i­bil­ity, and bee­tles with bril­liant white scales, mea­sur­ing a slim five mi­crom­e­ters. In fact, th­ese struc­tures are so im­pres­sive that they can out­per­form ar­ti­fi­cially en­gi­neered struc­tures that are 25 times thicker.

Ad­he­sion

Gecko feet can bind firmly to prac­ti­cally any solid sur­face in mil­lisec­onds, and de­tach with no ap­par­ent ef­fort. This ad­he­sion is purely phys­i­cal with no chem­i­cal in­ter­ac­tion be­tween the feet and sur­face.

The ac­tive ad­he­sive layer of the gecko’s foot is a branched nanoscopic layer of bris­tles called “spat­u­lae”, which mea­sure about 200 nanome­ters in length. Sev­eral thou­sand of th­ese spat­u­lae are at­tached to mi­cron sized “seta”. Both are made of very flex­i­ble ker­atin. Though re­search into the finer de­tails of the spat­u­lae’s at­tach­ment and de­tach­ment mech­a­nism is on­go­ing, the very fact that they op­er­ate with no sticky chem­i­cal is an im­pres­sive feat of de­sign.

Gecko’s feet have other fas­ci­nat­ing fea­tures too. They are self-clean­ing, re­sis­tant to self-mat­ting (the seta don’t stick to each other) and are de­tached by de­fault (in­clud­ing from each other). Th­ese fea­tures have prompted sug­ges­tions that in the fu­ture, glues, screws and riv­ets could all be made from a sin­gle process, cast­ing ker­atin or sim­i­lar ma­te­rial into dif­fer­ent moulds.

Por­ous strength

The strong­est form of any solid is the sin­gle crys­tal state – think di­a­monds – in which atoms are present in near per­fect or­der from one end of the ob­ject to the other. Things like steel rods, air­craft bod­ies and car pan­els are not sin­gle crys­talline, but poly­crys­talline, sim­i­lar in struc­ture to a mo­saic of grains. So, in the­ory, the strength of th­ese ma­te­ri­als could be im­proved by in­creas­ing the grain size, or by mak­ing the whole struc­ture sin­gle crys­talline.

Sin­gle crys­tals can be very heavy, but na­ture has a so­lu­tion for this in the form of nanos­truc­tured pores. The re­sul­tant struc­ture – a meso-crys­tal – is the strong­est form of a given solid for its weight cat­e­gory. Sea urchin spines and nacre (mother of pearl) are both made of meso-crys­talline forms. Th­ese crea­tures have light­weight shells and yet can re­side at great depths where the pres­sure is high.

In the­ory, meso-crys­talline ma­te­ri­als can be man­u­fac­tured, although us­ing ex­ist­ing pro­cesses would re­quire a lot of in­tri­cate ma­nip­u­la­tion. Tiny nanopar­ti­cles would have to be spun around un­til they line up with atomic pre­ci­sion to other parts of the grow­ing mesocrys­tals, and then they would need to be gelled to­gether around a soft spacer to even­tu­ally form a por­ous net­work.

Bac­te­rial nav­i­ga­tion

Mag­ne­to­tac­tic bac­te­ria pos­sess the ex­tra­or­di­nary abil­ity to sense minute mag­netic fields, in­clud­ing the Earth’s own, us­ing small chains of nanocrys­tals called mag­ne­to­somes. Th­ese are grains sized be­tween 30–50 nanome­ters, made of ei­ther mag­netite (a form of iron ox­ide) or, less com­monly, greghite (an iron sul­phur combo). Sev­eral fea­tures of mag­ne­to­somes work to­gether to pro­duce a fold­able “com­pass nee­dle”, many times more sen­si­tive than man-made coun­ter­parts.

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