Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

MIT engineers probe spiders' polymer art

31.10.2006
Manufactured silk could be used for artificial tendons, parachutes, more

A team of MIT engineers has identified two key physical processes that lend spider silk its unrivaled strength and durability, bringing closer to reality the long-sought goal of spinning artificial spider silk.

Manufactured spider silk could be used for artificial tendons and ligaments, sutures, parachutes and bulletproof vests. But engineers have not managed to do what spiders do effortlessly.

In a study published in the November issue of the Journal of Experimental Biology, Gareth H. McKinley, professor of mechanical engineering, and colleagues examined how spiders spin their native silk fibers, with hopes of ultimately reproducing the process artificially.

McKinley heads the Non-Newtonian Fluid Dynamics research group in MIT's Department of Mechanical Engineering. Non-Newtonian fluids behave in strange and unexpected ways because their viscosity, or consistency, changes with both the rate and the total amount of strain applied to them.

Spider silk is a protein solution that undergoes pronounced changes as part of the spinning process. Egg whites, another non-Newtonian fluid, change from a watery gel to a rubbery solid when heated. Spider silk, it turns out, undergoes similar irreversible physical changes.

Stickiness and Flow

McKinley and Nikola Kojic, a graduate student in the Harvard-MIT Division of Health Sciences and Technology, studied the silk of Nephila clavipes, the golden silk orb-weaving spider. One species of golden orb spider creates a web so strong it can catch small birds. In the South Pacific, people make fishing nets out of this web silk.

The researchers chose the golden silk spider because of the formidable strength of its web. But Kojic was taken aback when the first palm-sized spider crawled out of the box he received in the mail from an accommodating employee of Miami's MetroZoo. (She simply gathered some up from the grounds; the zoo does not exhibit golden orb spiders.)

"This is pretty scary," he said. "I'd never seen a spider this big. I never grew up around anything with furry knuckles." But he quickly settled into dissecting the peanut-sized and -shaped protuberance on the spiders' backs containing their silk-producing glands and spinnerets.

Spiders don't actually spin ("spinning" refers to the age-old art of drawing out and twisting fibers to form thread); instead, they squirt out a thick gel of silk solution. (One teaspoonful can make 10,000 webs.) They then use their hind legs as well as their body weight and gravity to elongate the gel into a fine thread.

Kojic, who first practiced on silkworms, learned how to extract a microscopic amount of the gel-like solution from the spider's silk-producing major ampullate gland.

The researchers used devices called micro-rheometers-custom-made to handle the tiny drops of silk solution-to test the material's behavior when subjected to forces. The team tested the thick solution's viscosity, or how it flowed, by "shearing" it, or placing it between two rapidly moving glass plates. They tested its stickiness by pulling it apart, like taffy, between two metal plates.

The magic that makes silk so strong, the researchers discovered, happens while it flows out of the spider's gland, lengthens into a filament and dries.

Engineering Nature

The key to spider silk is polymers.

Plastics, Kevlar (used in bulletproof vests) and parts of the International Space Station are some of the many items made from polymers. The proteins in our bodies are polymers made from amino acids. From the Greek for "many" and "units," polymers are long linked chains of small molecules. They can be flexible or stiff, water-soluble or insoluble, resistant to heat and chemicals and very strong.

Silk protein solution consists of 30-40 percent polymers; the rest is water. The spider's silk-producing glands are capable of synthesizing large fibrous proteins and processing those proteins into an insoluble fiber.

"The amazing thing nature has found is how to spin a material out of an aqueous solution and produce a fiber that doesn't re-dissolve," McKinley said. Like a cooked egg white, dry spider silk doesn't revert to its former liquid state. What started out as a water-based solution becomes impervious to water.

The silk protein's long molecules are like tangled spaghetti. They form a viscous solution but are slippery enough to slide past each other easily and squeeze through the spider's ampullate gland. As the silk gel flows from the gland through an S-shaped, tapered canal to the outside of the spider's body, the long protein molecules become aligned and the viscosity (or resistance to flow) drops by a factor of 500 or more.

As the resulting liquid exits the abdomen through the spinneret, it has the characteristics of a liquid crystal. It's the exquisite alignment of the protein fibers, Kojic said, that gives silk threads their amazing strength.

While the silk stretches and dries, it forms miniscule crystalline structures that act as reinforcing agents. Engineered nanoparticles-tiny materials suspended in artificial silk-may be able to serve the same purpose.

In conjunction with the polymer synthesis and analysis work of Paula T. Hammond, an MIT professor of chemical engineering, McKinley's laboratory will use the new insights about spider silk to team up with MIT's Institute for Soldier Nanotechnologies to emulate the properties of silk through polymer processing.

"We're interested in artificial materials that emulate silk," McKinley said. Tailoring the properties of the liquid artificial spinning material to match the properties of the real thing "may prove essential in enabling us to successfully process novel synthetic materials with mechanical properties comparable to, or better than, those of natural spider silk," the authors wrote.

This work was supported by the NASA Biologically Inspired Technology Program, the DuPont-MIT Alliance and the MIT Institute for Soldier Nanotechnologies.

Elizabeth A. Thomson | MIT News Office
Further information:
http://www.mit.edu

More articles from Materials Sciences:

nachricht Move over, Superman! NIST method sees through concrete to detect early-stage corrosion
27.04.2017 | National Institute of Standards and Technology (NIST)

nachricht Control of molecular motion by metal-plated 3-D printed plastic pieces
27.04.2017 | Ecole Polytechnique Fédérale de Lausanne

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Making lightweight construction suitable for series production

More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.

Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...

Im Focus: Wonder material? Novel nanotube structure strengthens thin films for flexible electronics

Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.

"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...

Im Focus: Deep inside Galaxy M87

The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.

Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...

Im Focus: A Quantum Low Pass for Photons

Physicists in Garching observe novel quantum effect that limits the number of emitted photons.

The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...

Im Focus: Microprocessors based on a layer of just three atoms

Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.

Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Fighting drug resistant tuberculosis – InfectoGnostics meets MYCO-NET² partners in Peru

28.04.2017 | Event News

Expert meeting “Health Business Connect” will connect international medical technology companies

20.04.2017 | Event News

Wenn der Computer das Gehirn austrickst

18.04.2017 | Event News

 
Latest News

Wireless power can drive tiny electronic devices in the GI tract

28.04.2017 | Medical Engineering

Ice cave in Transylvania yields window into region's past

28.04.2017 | Earth Sciences

Nose2Brain – Better Therapy for Multiple Sclerosis

28.04.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>