January 17, 2002. Copyright 2001. Graphic News. All rights reserved.

Spinning silk from goatÕs milk

LONDON, January 17, Graphic News: Scientists have mimicked spiders to produce silk superfibres that are three times tougher than Kevlar and ounce per ounce five times stronger than steel.

The common garden spider (Araneus diadematus) produces silk with extraordinary properties -- a process that has been perfected through 400 million years of evolution. Now researchers at Nexia Biotechnologies Inc. in Canada and the U.S. Army Soldier Biological Chemical Command have reported in this weekÕs journal of Science that they have made the worldÕs first silk fibres from man-made materials with properties similar to natural spider silk. 

Spider silk has long been admired by material scientists for its unique combination of high-performance properties including toughness, strength, lightness and biodegradability. Despite its superior properties, spider silk is not used commercially because of lack of availability. Spider farming is simply not practical. Unlike silk worms, the spiderÕs territorial and aggressive nature precludes intensive cultivation. Further, it is not the spider cocoon silk that is desired but certain components of the web silk, namely the ÒdraglineÓ or ÒframeÓ silk which is used to construct the spokes of a spider web. Now Nexia has developed a recombinant spider silk which they have named BioSteel.

ÒMimicking spider silk properties has been the holy grail of material science for a long time and now weÕve been able to make useful fibres,Ó said Dr. Jeffrey Turner, President and CEO of Nexia. ÒHaving achieved this proof of principle, Nexia has now moved toward commercial development for multiple applications such as medical sutures, biodegradable fishing lines, soft body armour and unique material composites.Ó

Dragline silk exhibits a combination of strength and toughness unmatched by high-performance synthetic fibres -- it is the strongest natural fibre known, with a tensile strength of 400,000 lb per square inch (28,000 kg per square cm).

ÒItÕs incredible that a tiny animal found literally in your backyard can create such an amazing material by using only amino acids, the same building blocks that are used to make skin and hair,Ó added Dr. Turner. ÒSpider silk is a material science wonder -- a self-assembling, biodegradable, high-performance, nanofibre structure one-tenth the width of a human hair that can stop a bee travelling at 20 miles per hour (32 km per hour) without breaking. Spider silk has dwarfed ManÕs achievements in material science to date.Ó

Anthoula Lazaris and colleagues at Nexia had to overcome two sets of problems. First they had to isolate the gene from the spider that codes for the silk protein, then introduce the spider silk gene into a system that can read the genetic instructions and produce authentic silk proteins.

Spider silk genes are long and repetitive. Bacterial and other fermentation systems, which work well with other recombinant proteins, are inadequate in producing silk protein. The primitive bacteria appear to truncate silk genes because of their repetitive nature, thus leading to shorter silk proteins.

The Nexia researchers inserted two sets of spider silk genes into baby hamster kidney and cow cells to produce silk proteins. They then spun the proteins from an aqueous solution and stretched them into fine silk fibres with the strength and toughness, although somewhat less tenacity, of the natural dragline silk.

Having successfully proved that spider genes could make mammalian cells produce dragline silk proteins in the laboratory, the researchers had to come up with a way to mass-produce the protein. They exploited the anatomical similarities between the spider silk gland and goat mammary glands. In both cases, epithelial cells -- the cells which line most internal organs and glands -- manufacture and secrete water soluble, complex proteins in large amounts. Dairy animals are ideal for this job because they have a very large number of mammary cells.

The researchers genetically-engineered the spider genes into goat embryos which were then cloned in a similar way to Dolly the sheep. The first two BioSteel transgenic goats, named Webster and Peter, were born in January 2000. Webster and Peter -- who carry a single spider silk gene in their genetic make-up of 70,000 goat genes -- now have the enviable job (in goat terms at least) of siring a large herd of dairy goats. Their milk will supply the proteins to provide industrial quantities of BioSteel for spinning and product development.

/ENDS

Sources: Science, Nexia Biotechnologies Inc.