Doing Biomimicry: Mechanical Principles

Steven Vogel's book Cats' Paws and Catapults contains an excellent list of nature's design principles for mechanical engineers1.   It is reproduced here, with some editing for brevity and links.  For more explanation of the principles, see the book.

"Nature uses fewer flat and more curved surfaces than we do", for better lightweighting.

Corners in our technology are abrupt; nature's are generally rounded, to avoid stress concentrations.

Nature uses curved surfaces and rounded corners (Photo: Jeremy Faludi)
Industry makes things out of many components, each of which is homogeneous; nature makes things out of fewer components but they vary internally.
Bone is a single material that varies a great deal in its construction.
(Modified from Wikimedia Commons)
"Nature's designs take advantage of diffusion, surface tension, and laminar flow"; we mostly use gravity, thermal conductivity, and turbulence.
We design for stiffness, nature designs for strength and toughness.

Brick walls (left) are generally built for stiffness;
abalone shells (right) are like a brick wall in their microstructure,
but with flexible "mortar" that makes them twice as strong
and a thousand times tougher than their "bricks" alone.  (Image Sources 1, 2)

Our mechanisms have rigid pieces moving on sliding contacts, "nature's objects bend, twist, or stretch at predetermined places".

This vibration damping system for film soundtrack readers
replaced roughly $50 of rigid machined arms, high-precision ball bearings,
springs, and an air shock absorber with roughly $1.50 of spring steel
and viscoelastic foam, for the same noise reduction.  
(Photo and device design: Jeremy Faludi)

"We minimize drag with streamlined bodies of fixed shape", nature uses "nonrigid bodies that reconfigure in flows".
Jellyfish are not streamlined rigid bodies;
rather, they change their shape to move through water.
(Photo: Jeremy Faludi)
Industry uses bulk metals, but nature never does--we use metal's ductility to avoid crack propagation, while nature uses foams and composites to do so.

The Eiffel Tower uses steel to bend rather than break under stress;
trees use wood, a foamed composite, to do the same. (Photos: Jeremy Faludi)

We usually load materials in compression, nature very often loads in tension.  (Buckminster Fuller called this "Tensegrity".)

Kenneth Snelson's sculpture "Needle Tower" uses tensegrity for its extremely lightweight form.  
(Wikimedia Commons)

"Structures with tensile sheaths outside and pressurized fluid inside are both more common and more diverse in nature's designs than in ours."  Nature also usually uses water, we usually use a gas.

Tires are one of the few places we use fluid pressure to create structure.

We use the wheel extensively, nature almost never does.
Our engines mostly use rotation or expansion, "most of nature's are based on sliding or contracting".

Muscles work by contracting linearly.

"Many of our engines extract energy from temperature differences, whereas all natural engines [such as photosynthesis and the Krebs cycle] are isothermal."

The Krebs cycle is how humans and many other organisms turn
food into energy in our bodies.  It is an isothermal reaction.  
(Modified from Wikimedia Commons)

Nature mostly stores mechanical work as elastic energy, sometimes as gravitational potential energy; we usually store work electrically or kinetically.

Kangaroos' Achilles tendons capture the energy from hitting the ground
as elastic energy, and re-release it for the next jump. 

Our pipes trade off pressure drop for volume of flow, nature hardly ever does.
We use surface boats, "nature overwhelmingly prefers submarines".

While many birds pass time on the water's surface, they either fly or dive for serious locomotion.  
Moving on the surface causes too much drag at high speed.  (Wikimedia Commons)

Nature's factories often produce things larger, not smaller, than themselves.  (e.g. seeds to trees, spiders to their webs, mothers to children)
Nature's devices need constant maintenance [but often self-repair].

A type of concrete invented at the University of Michigan's Materials Research Lab
heals itself after cracking, through special chemical reactions with air.  

"Our technology is as dry as nature's is wet."


1Vogel, S. "Cats’ paws and catapults: mechanical worlds of nature and people"  WW Norton & Company, New York, 1998.  pp.289-291.