Sunday, 14 April 2013

Talk : Smart Materials (Part 1)

Nottingham Trent University recently hosted the Inaugural Lecture of Dr Philip Breedon, Reader in Smart Technologies, School of Architecture Design and the Built Environment.

Titled “Materials intelligence: Informing Smart Design” the lecture looked at a number of emerging technologies and materials, and their potential links with innovative design, looking particularly at materials that mimicked structures found in nature.

To start with, Dr Breedon reviewed some of the items that came up with on an internet search for “smart design”, showing that it covered a wide range of applications, ranging from clever furniture design to using a bulldog clip on s fridge shelf to make a stop for an ad-hoc bottle stack.

Dr Breedon then summarised the key features of “smart behaviour”, which included that the material should :
a) Sense a stimulus from the environment and react (e.g. reactive lenses)
b) The reaction should be reproducible and reversible (e.g. thermochromic paints)
c) Need to be part of a system, cannot be a material in isolation.

Combining “Smart Materials” and “Smart Behaviour” gives the field of “Smart Design”

Dr Philip Breedon. I mean who else did you expect? Mr T?

Dr Breedon then took a fascinating journey through some of todays most interesting technologies, with particular reference to Biomimetic materials (materials that take inspiration from nature to define new engineering and design solutions, which forms the basis for this post, together with a few extra snippets of info from the Interweb.

Human subtlety...will never devise an invention more beautiful, more simple or more direct than does nature, because in her inventions nothing is lacking, and nothing is superfluous. (Leonardo Da Vinci)

The hook-and-loop fastener was conceived in 1941 by Swiss engineer, George de Mestral. The idea came to him one day after he took a close look at some burdock seed heads that kept sticking to his clothes and his dog's fur. He examined them under a microscope, and noted their hundreds of "hooks" that caught on anything with a loop, such as clothing, animal fur, or hair.

It took until 1951 for de Mestrel to develop the technology – in particular an industrial production system - and it was at this point that he filed a patent.

But it not until the 1960’s, when NASA took up the material for use in spacesuits and on spacecraft, that it really began to be noticed.

Gecko Setae
The nanosized hairs on a Gecko’s feet enable it to be in actual contact with a much larger proportion of the surface it is walking on than would be the case if its feet has a flat surface. It is often the case that two surfaces in intimate contact will generate a small adhesive force between themselves- the trick is to ensure that the surfaces are really in close contact. And the many tiny hairs allow the gecko to do exactly that. Perhaps unsurprisingly, there has been great interest in the possibility of a synthetic version of this natural adhesive, which has resulted in “Gecko Tape” and a experimental "Stickybot".

However, there have been challenges in making synthetic setae work in wet conditions, and also in replicating the self-cleaning behaviour of the real gecko setae.

Gecko feet - very, very, clever. Puts Nike in their place.

Off topic, but this is a Oligocene-era Gecko trapped in amber. How cool is that?

Stenocara Beetle
To drink water, the Stenocara beetle catches fog droplets on its hardened wings. The water droplets from the fog gather on small hydrophilic bumps, and avoid the rest of the surface which is hydrophobic. Eventually, the droplets become so large that they roll down to the beetles mothparts. NBD Nano have emulated this capability by creating a textured surface that combines alternating hydrophobic and hydrophilic materials. Potential uses include extracting moisture from the air in desert areas (see also here)

The Stenocara Beetle, with built-in water collection system

Shape Memory Alloys (SMA’s)
These interesting materials, often based on alloys such as Nitinol can be engineered to reversibly change shape at a particular temperature, a feature that Dr Breedon demonstrated by placing an extended SMA spring into a beaker of hot water…

An uncoiled SMA spring

…which caused it to instantly shrink into a tight coil!

...which instantly reverts to a tight coil when placed in hot water

SMA’s are already widely used in medical devices such as stents (which dilate constricted or blocked blood vessels). See also here

An SMA stent - already widely used in clinical applications

Photuris firefly
Researchers have noticed that the irregular scales on the back of fireflies improve the percentage of light that is emitted from the insect, and a synthetic version has shown a 50% improvement in the light emission of a standard LED. Awesome! (see here for more details)

Strength vs Stiffness
Dr Breedon mentioned a 1995 essay by Steve Vogel which describes the different approaches man and nature have taken in building structures. The first paragraph pretty much sets the scene :
Look at a hinge on the nearest door. Its halves slide smoothly around each other and around their centering pin. Then look at the ears of a cat or dog as it turns to face some rustle or squeak. Muscles pull on cartilage, twisting each structure around its pivot, and skin stretches to accommodate the motion. These ears are hinges, too, but they’re made from flexible materials that bend instead of solid parts that slide.(Steven Vogel 1995)

and also commented on how natural structures have graded properties (think of the different density of bone on its surface and interior) and have control and feedback mechanisms built in.

Sea Cucumber
Another good example of the clever design shown in nature is that of the Sea Cucumber, which has an exoskeleton made of “catch connective tissue". This collagenous material is composed of very fine cellulose fibres, which are made to bind together or loosen depending on which protein is released by the surrounding cells. In the case of Sea Cucumbers, the tissue hardens when the creature is under attack, while Starfish use the capability to change from moving flexibly around the seabed to becoming rigid while prying open a bivalve mollusc or preventing itself from being extracted from a crevice.

Researachers have tried to use these fibres for medical electrodes that do not provoke the scarring seem with metal electrodes.

A Sea Cucumber - not good in a salad...

The Remora Fish
The Remora Fish is the one that you often see on wildlife programs swimming right underneath sharks and the like.

A Remora fish hitching a ride on a Manta Ray

Surprisingly, they are actually attached to the host fish by a special pad on their upper body.

A Remora, looking for a ride

Sorry sunshine, that jar ain't going anywhere..

And researchers suspect that one key to this is the many microscopic have found that the adhesion is passive and achieved by rows of plate-like structures called lamellae, from which perpendicular rows of tooth-like structures called spinules emerge. The team hope that understanding the mechanism by which these structures work may allow the development of pain- and residue-free bandages or ways of attaching sensors to underwater objects.

Sandcastle worm
This seashore creature forms protective tubes by secreting a two part adhesive that is used to glue sand and other mineral particles together. Researchers are investigating the possibility that this may form the basis of a biocompatible glue that can be used to repair shattered bones, instead of the pins and screws that are used currently. Other species that produce underwater glues include certain species of mussels, oysters, barnacles and caddisfly larvae.

Know your Miuras
A Miura fold is a type of fold (invented by Japanese astrophysicist Koryo Miura> which allows a large flat sheet (such as a solar array) to be unfolded with a single action from a very compact folded package, and is also the type of fold that allows leaves to package themselves into tiny buds before they emerge (see also this great article...and this great article)

Hornbeam leaves unfold using a Miura fold

The other Miura is the ground breaking supercar built by Lamborghini in the late 1960s, and example of which famously comes to a sticky end in the opening sequence of The Italian Job.

A Lamborghini Miura, the first supercar of the modern age - but of little use as a smart material

It’s important to ensure your audience knows which one you are talking about!

Part 2
Dr Breedon then discussed some of the relevant research being undertaken at NTU, which is covered in Part 2 of this post

Image Sources
All images NSB's own, except for the following:
Stenocara, Stent, Sea Cucumber, Remora, Remora on manta, Remora Jar, Leaves, Miura(the car)

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