The Might of the Spider
Spider silk is a protein fiber spun by spiders. Spiders use their silk to make webs or other structures, which function as nets to catch other animals, or as nests or cocoons for protection for their offspring. Spider silk is as strong as many industrial fibers. There is commercial interest in duplicating spider silk artificially, since spiders use renewable materials as input and operate at room temperature, low pressures and using water as a solvent. However, it has been difficult to find a commercially viable process to mass produce spider silk.
Using spiders to make their silk is a bit like herding cats. Spiders tend to be territorial and aggressive. So other methods must be used.
Finer than human hair, five times stronger by weight than steel, and three times tougher than the top quality man-made fiber Kevlar, spider silk is an ideal material for numerous applications. Suggested industrial applications have ranged from parachute cords and protective clothing to composite materials in aircrafts.
To develop a more sustainable process, can scientists mass-produce artificial silk while maintaining the amazing properties of native silk? That is something Sang Yup Lee at the Korea Advanced Institute of Science and Technology (KAIST) in Daejeon, the Republic of Korea, and his collaborators, Professor Young Hwan Park at Seoul National University and Professor David Kaplan at Tufts University, want to figure out. Their method is making the soluble silk proteins into water insoluble fibers through spinning.
Others have earlier artificially spun such fibers making silk fiber with a diameter of about 30 micrometers.
For the successful expression of high molecular weight spider silk protein, Professor Lee and his colleagues pieced together the silk gene from chemically synthesized oligonucleotides, and then inserted it into host. Initially, the bacterium resisted making this complex protein. “To make E. coli synthesize this ultra high molecular weight spider silk protein having highly repetitive amino acid sequence, we helped E. coli overcome the difficulties by systems metabolic engineering,” says Sang Yup Lee, Distinguished Professor of KAIST, who led this project.
The KAIST team performed high-cell-density cultures for mass production of the recombinant spider silk protein. Then, the team developed a simple, easy to scale up purification process for the recombinant spider silk protein. The purified spider silk protein could be spun into beautiful silk fiber. To study the mechanical properties of the artificial spider silk, the researchers determined tenacity, elongation, and Young’s modulus, the three critical mechanical parameters that represent a fiber’s strength, extensibility, and stiffness. Importantly, the artificial fiber displayed the tenacity, elongation, and Young’s modulus of 508 MPa, 15%, and 21 GPa, respectively, which are comparable to those of the natural spider silk.
Perhaps one day artificial spider silk will be instrumental in air craft, cars, and clothing The key will be in doing it economically..
This current work is published on July 26 in the Proceedings of the National Academy of Sciences online.
For further information: http://www.kaist.edu/english/01_about/06_news_01.php?req_P=bv&req_BIDX=10&req_BNM=ed_news&pt=17&req_VI=2834 or http://en.wikipedia.org/wiki/Spider_silk