Nature as engineer: what nature teaches us
Evolution has run a research and development programme for about 3.5 billion years. On the calendar in The universe in one year: a cosmic calendar that is about three months, most of it spent on microbes, and it started from the poorly understood beginning described in Life's origin: what we know and what we don't. The designs that survived are good enough to be worth studying. Biomimicry (a word popularised by Janine Benyus in her 1997 book) means learning a principle from a living thing and using it in engineering.
The stress is on principle. Almost every successful case copies a mechanism, not a shape, and nature is not an optimiser. Evolution, the idea at the heart of Five ideas that built modern science, produces what is good enough with the materials and the history at hand, and engineers have steel, concrete and electricity as well. Here are eight cases, with the hype checked.
1. Burdock and Velcro (1941, 1955)
In 1941 the Swiss engineer George de Mestral came back from a hunting trip in the Swiss mountains with burrs of burdock stuck to his clothes and his dog's fur. Under a microscope he saw tiny hooks catching loops. Turning that into a product took years: cotton versions frayed, so he switched to nylon, worked with a weaver in Lyon and found that infrared light could set the hooks. The Swiss patent was filed in 1951 and granted in 1955. The name joins velours (velvet) and crochet (hook).
BEFORE PRESSED TOGETHER
=== loop tape ========
() () () () () ======================
(J) (J) (J) (J) (J)
J J J J J ======================
=== hook tape ======== each loop is caught by a hook
SHEAR (pull sideways): every hook holds its loop, so it is very strong.
PEEL (lift one edge): hooks let go one row at a time, which is easy.
That is the "rrrip" you hear.
Burdock burr (nature): hooked bracts catch the loops in cloth or fur.
Velcro (1941 idea, 1955 patent): nylon hooks and nylon loops.2. The lotus leaf: surfaces that clean themselves
Lotus leaves stay clean in muddy water. Wilhelm Barthlott and Christoph Neinhuis studied why with the electron microscope and published their 1997 paper on the sacred lotus's "escape from contamination". The leaf has a double structure: bumps (papillae) 10 to 20 micrometres high, covered in wax crystals. Water cannot enter the gaps, so the drop rests on air and on a few percent of the surface.
SMOOTH WAX LEAF LOTUS LEAF
contact angle about 105 degrees contact angle about 160 degrees
.-""""-. .-""""-.
.' '. .' '.
/ \ / \
| | | |
| | \ /
\ / `-. .-'
`-.______.-' `-.__.-'
---------------------------- /\/\/\/\/\/\/\/\/\/\/\/\/\/\
flat wax: the drop sags and papillae 10-20 um high, covered
spreads, wide contact area in wax: air stays trapped between
the tips, under the drop
Cassie-Baxter: cos(angle) = f x (cos(wax angle) + 1) - 1
f = share of the drop that touches solid = 5%, wax angle = 105 deg
cos(angle) = 0.05 x (-0.259 + 1) - 1 = -0.963 -> angle = 164 deg
SELF-CLEANING (tilt the leaf a few degrees; o = dirt grain)
.-"-.
( oo )--> o o o o
`-._.-'
/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\
grains stick to the drop more than to the leaf, so they leave with itThe calculation shows why texture matters: a wax surface alone gives about 105 degrees, but touching only 5% of the solid pushes the angle to about 164. Paints and coatings based on it appeared around 1999. The limits are real. The effect works for water, not oils or solvents, and the delicate texture wears off.
3. Gecko feet: glue-free grip
A gecko climbs glass without glue, suction or sticky liquid. Kellar Autumn's group showed in 2000 that one hair (a seta) pulls with about 200 micronewtons, and in 2002 that the force is the weak van der Waals attraction between molecules, because geckos grip water-loving and water-hating surfaces equally well.
1. TOE PAD (about 1 cm wide)
========= ========= ========= ========= =========rows of ridges
(lamellae)
|
v zoom x100
2. SETAE (hairs ~100 um long, ~5 um thick, ~14,000 per mm^2)
\ \ \ \ \ \ \ \ \ \ \ \ \ angled hairs:
\ \ \ \ \ \ \ \ \ \ \ \ \ grip when pulled,
let go when peeled
|
v zoom x50
3. ONE SETA branches at its tip
\ | / about 200 uN of pull
\|/ from one hair
| (Autumn et al., 2000)
,-. ,-. ,-. ,-.
|
v zoom x100
4. SPATULAE: ~1000 flat tips per seta, each ~200 nm wide
_____ _____ _____ _____ _____ _____ _____
============================================= wall
Between tip and wall (gap under 1 nm) molecules attract each other
weakly (van der Waals force). Billions of tips add up to a strong grip.Check the arithmetic: about 6.5 million setae times 194 micronewtons is 1,260 newtons, enough to hold roughly 130 kg if every hair gripped at once. No gecko uses them all, and the hairs release by changing their angle, which is why the animal can peel a foot off in a few hundredths of a second. In 2003 Andre Geim's group at Manchester made an early "gecko tape" from polymer hairs. Synthetic versions now exist as grippers and climbing-robot feet, but they collect dust and wear out far sooner than a real foot, which cleans itself as it walks.
4. The kingfisher and the 500 series
Early bullet trains had a problem. A train entering a tunnel at speed pushes the air ahead like a piston, and that compression leaves the far mouth as a loud boom. Making trains faster made the boom worse. Eiji Nakatsu, an engineer at JR West and a bird-watcher, noticed that a kingfisher dives from thin air into dense water with hardly a splash, thanks to its long tapered beak. The 500 series (service from March 1997, 300 km/h) has a nose about 15 m long.
A. BLUNT NOSE (bullet shape)
the cross-section grows fast
############################### air is pushed aside at once:
################################## a steep pressure step forms;
################################### in a tunnel: a boom
####################################
###################################
##################################
###############################
B. LONG TAPERED NOSE (500 series)
a nose about 15 m long
###### air parts gradually: the
################# pressure rises gently, so
########################### the tunnel boom is weaker
####################################
###########################
#################
######
C. KINGFISHER HEAD AND BEAK
a dagger beak, then the wider head
## diving from thin air into
########## dense water with little
############o##### splash needs the same ramp
####################################
##################
##########
##The physics is sound: the more gradually the cross-section grows, the more gently the air pressure rises. Reported results are about 10% higher speed and 15% lower energy use compared with the older design, but sources differ on details. Wind-tunnel tests and computer simulation shaped the final nose, with the bird as inspiration, and the same team reportedly gave the pantograph owl-like serrations to cut noise.
5. Termites and the Eastgate Centre (a cautionary case)
The Eastgate Centre in Harare, Zimbabwe (1996, architect Mick Pearce with the engineers at Arup) is often said to copy a termite mound. It has no conventional air conditioning. Concrete slabs and ducts are chilled by night air, daytime air passes over the cold mass, and warm air rises through an atrium and chimneys. Reported energy use is around a third of comparable buildings, and some sources claim far less.
^ ^ ^ ^ ^
warm air leaves by the chimneys
| | | | | | | |
| | | | | | | |
+----------------------+ | | | | | | | | +----------------------+
| -> ATRIUM <- |
| OFFICES | | OFFICES |
| | air rises (stack | |
|======================| effect) from the |======================|
| | warm offices | |
| ^ ^ ^ | | ^ ^ ^ |
| | | |
|======================| |======================|
| | | |
| ^ ^ ^ | | ^ ^ ^ |
| | | |
|======================| |======================|
| -> | | <- |
| fans | | fans |
+------------------------------------------------------------------+
= concrete slabs and ducts: thermal mass
NIGHT: cool outside air is pushed through them and chills the concrete.
DAY: incoming air passes the cold concrete, warms up in the offices,
and rises out through the atrium and chimneys. No big cooling plant.Here the biology needs a caveat. Termite expert Scott Turner describes the mounds of Macrotermes as something closer to a lung than an air conditioner, and field studies by Mahadevan's group found that airflow in mounds reverses twice a day, driven by daily temperature swings. Eastgate also uses heavy concrete and powered fans, which termites do not. So it is best called termite-inspired: sound physics (night flushing), only loosely termite biology. The building works either way.
6. Shark skin
Shark skin is covered in tiny ridged scales. Grooves (riblets) a few tens of micrometres wide and aligned with the flow stop the small swirls in the boundary layer from touching the surface at full strength, which cuts friction drag by up to about 5 to 10% in lab tests. NASA research led to riblet film that 3M made, tested on racing yachts and on an Airbus A320. Today a film called AeroSHARK flies on Lufthansa Group long-haul jets with a claimed saving of about 1% of fuel. That sounds modest, but friction is only about half of an airliner's drag and the film covers part of the aircraft. The "shark-skin" swimsuits of 2000 are a warning: studies suggested their benefit came mostly from compression and slippery fabric, and the polyurethane suits that followed were banned in 2010.
7. Spider silk
Dragline silk is about 1.1 gigapascals strong at a density of 1.3 g/cm3. High-strength steel, say 1.5 GPa at 7.85 g/cm3, is stronger in absolute terms, but weight for weight silk is about four times better. Its toughness, the energy absorbed before breaking, is around 160 megajoules per cubic metre against roughly 50 for Kevlar and 6 for steel (measurements from the 1990s by Gosline and colleagues). A spider makes it at room temperature from a water-based protein solution, which then solidifies as it flows through a narrow duct. Spiders cannot be farmed, as they eat each other, so companies make silk-like proteins by fermentation with bacteria or yeast. Matching the natural fibre at industrial scale is still hard, especially the spinning step.
8. Ants and swarms
Ants find short routes without a leader. In the double-bridge experiments of Goss and Deneubourg (1989 and 1990) Argentine ants chose between a short and a long branch to food, and most ended up using the short one. The mechanism: each ant lays a chemical trail, the short path is completed sooner so its trail strengthens first, more ants follow, and the long trail evaporates.
t = 0 no trail yet: ants pick a path at random
.................................................................
. .
. long path: more steps per trip .
+------+ +------+
| NEST |........................................................| FOOD |
+------+ +------+
short path: fewer steps per trip
t = 1 short-path ants return sooner, so its trail grows first
.................................................................
. .
. long path: more steps per trip .
+------+ +------+
| NEST |========================================================| FOOD |
+------+ +------+
short path: fewer steps per trip
t = 2 more ants follow the strong trail, which makes it stronger
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. .
. long path: more steps per trip .
+------+ +------+
| NEST |########################################################| FOOD |
+------+ +------+
short path: fewer steps per trip
# strong trail = medium . weak, evaporating
ACO rule: p(step) ~ trail^a x closeness^b ; each round:
trail <- (1 - r) x trail + Q / route length (evaporate, then deposit)Marco Dorigo turned this into ant colony optimisation in 1992, used since for vehicle routing, scheduling and network routing. On static travelling-salesman benchmarks specialised solvers do better, but ant methods suit problems where the map keeps changing. In robotics, Harvard's 2014 Kilobot swarm of 1,024 tiny robots, each costing about 14 dollars in parts, formed shapes using only neighbour-to-neighbour rules, and termite-inspired robots built simple structures.
What to take away
- Copy the principle, not the shape. Velcro uses nylon, Eastgate uses concrete. What carries over is hook-and-loop, night flushing, the slow ramp.
- Check the story. The kingfisher and the termites are widely told, but the numbers vary by source and the termite model is disputed. Lotus coatings and gecko tapes wear out.
- Nature is a library, not an oracle. Evolution satisfies; engineers can combine its tricks with materials and power sources it never had.
And it goes both ways. Biologists now use engineering to ask whether a feature is really optimal, and engineers have borrowed evolution itself, in the form of the directed evolution of enzymes. The most useful lesson may be the plainest one: look closely at the thing in front of you, as a man with a hunting dog and a microscope once did.