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 Physics, photosynthesis and solar cells
01.12.2016 | University of California - Riverside

nachricht New process produces hydrogen at much lower temperature
01.12.2016 | Waseda University

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Novel silicon etching technique crafts 3-D gradient refractive index micro-optics

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.

Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...

Im Focus: Quantum Particles Form Droplets

In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.

“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...

Im Focus: MADMAX: Max Planck Institute for Physics takes up axion research

The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.

The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...

Im Focus: Molecules change shape when wet

Broadband rotational spectroscopy unravels structural reshaping of isolated molecules in the gas phase to accommodate water

In two recent publications in the Journal of Chemical Physics and in the Journal of Physical Chemistry Letters, researchers around Melanie Schnell from the Max...

Im Focus: Fraunhofer ISE Develops Highly Compact, High Frequency DC/DC Converter for Aviation

The efficiency of power electronic systems is not solely dependent on electrical efficiency but also on weight, for example, in mobile systems. When the weight of relevant components and devices in airplanes, for instance, is reduced, fuel savings can be achieved and correspondingly greenhouse gas emissions decreased. New materials and components based on gallium nitride (GaN) can help to reduce weight and increase the efficiency. With these new materials, power electronic switches can be operated at higher switching frequency, resulting in higher power density and lower material costs.

Researchers at the Fraunhofer Institute for Solar Energy Systems ISE together with partners have investigated how these materials can be used to make power...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ICTM Conference 2017: Production technology for turbomachine manufacturing of the future

16.11.2016 | Event News

Innovation Day Laser Technology – Laser Additive Manufacturing

01.11.2016 | Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

 
Latest News

UTSA study describes new minimally invasive device to treat cancer and other illnesses

02.12.2016 | Medical Engineering

Plasma-zapping process could yield trans fat-free soybean oil product

02.12.2016 | Agricultural and Forestry Science

What do Netflix, Google and planetary systems have in common?

02.12.2016 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>