Stronger than steel but lighter than a piece of thread. It is difficult to beat Mother Nature when it comes to making something as tough as a spider web, writes
DICK AHLSTROM
NOTHING DELIVERED by scientists so far comes even close to what spider silk can do. It has a pulling or “tensile” strength comparable to high-quality steel, yet is so light that a single strand long enough to circle the earth would weigh less than half a kilo.
Now scientists in Germany believe they have a much clearer idea of what makes spider silk so amazing. They went back to ground level, getting down to the basics. Dr Frauke Gräter from the Heidelberg Institute for Theoretical Studies and colleagues started at the level of atoms to study the two main ingredients in spider silk.
One is a shapeless or “amorphous” goo while the other is a tough crystalline material. Separately they aren’t good for anything but together they deliver a remarkable substance, says Gräter.
“Silk fibres exhibit astonishing mechanical properties. They have an ultimate strength comparable to steel, toughness greater than Kevlar and a density less than cotton or nylon.”
The scientists separated the contributions made by these two ingredients. They found the soft material lets spider silk stretch up to 1.4 times its normal length without snapping. It also makes a finished web springy and able to absorb stress.
The crystalline material provides toughness, with spider silk achieving just the right balance between the two ingredients. The German team used models to test different mixtures of the two and showed there are definitely wrong ways of combining them. Simply stirring them together did not work, nor did lining them up in parallel. They showed that the best results came when the two parts were interspersed in a serial arrangement, a finding which they believe provides "a new structural model for silk". They published their findings yesterday evening in Cell Press's Biophysical Journal.
Their work might not deliver artificial spider silk next week but it does suggest a way forward. And one day they might be able to develop silks good enough to let a real Peter Parker take to the streets as Spider Man.
What can other animals teach us?
GECKOS happy sticky feet
If you’ve every watched a gecko run up a wall or even across a ceiling, you’ll know these lizards leave Spiderman in the shade. Many species of gecko have dry sticky toepads that let them cling to surfaces in a seemingly gravity-defying manner. These pads are covered with millions of tiny hair structures called setae, each of which splits into smaller extensions or tips called spatulae. Studies suggest that van der Waal’s forces between the spatulae and a surface allow the gecko to adhere to it. And don’t underestimate the force: a Tokay gecko can support its body mass with a single sticky toe. The gecko’s ability to hang around is inspiring scientists and engineers to come up with synthetic adhesives.
C. ELEGANS how to age well
The tiny soil-dwelling roundworm Caenorhabditis elegans (or C. elegans for short) may not be the most glamorous of animals, but it can teach us much about ageing. Because it’s easy to grow and it’s a lot less complex than we are, scientists use it as a “model” organism in the lab to look at how genetic mutations and the animal’s environment affect ageing.
The findings include that cool temperatures and dietary restrictions can help increase lifespan. There has to be an easier way.
BATS super-heroes of the night
Bats are surely among the most intriguing of mammals, with their ability to fly, and to detect objects using echo-location or “sonar” just like submarines do – by bouncing sound waves off them and detecting them as the waves return. Research at University College Dublin’s BatLab is looking at bat genetics to see what we can learn from the nocturnal creatures, particularly about inherited blindness and deafness. Bats may even be able to teach us more about ageing and the immune system, as well as how mammals evolved.
ANTS running with the gang
You seldom see one ant at a time – they are supremely social creatures that live in colonies ranging in size from tens up to millions of insects. That needs a bit of co-ordination to work, so how does one ant know what the others are up to? Ants send and receive chemical messengers called pheromones, which can communicate messages about where to find food, or if there’s danger about. Robotics researchers look at ant communication and behaviour to help design systems where robot swarms can “sense” each other or receive intructions using signals.
SHARKS not such a drag
Sharks make swimming look easy, and research has uncovered one of the secrets of their success. If you look at skin from some fast-swimming shark species up close with a scanning electron microscope you see tiny “riblets” on the surface. These ridge-like structures help to reduce drag close to the shark, meaning the animal can glide more easily through the water. A similar finish has been applied to boats, aircraft and swimsuits for serious athletes.
SNAKES watch your blood pressure
Seeing a snake about to bite could send your blood pressure sky high. But some snake venoms cause a rapid drop in blood pressure, resulting in shock and sometimes death. Figuring out the biochemistry behind these dramatic effects of Brazilian viper venom eventually led to the development of widely used ACE inhibitor drugs to control blood pressure.
- Claire O’Connell
