Léo RamosSpider silk: strength and elasticity transferred to a protein-based biopolymerLéo Ramos
On movie screens and in comic books, the superhero moves about the metropolis while hanging from strong silk filaments that are also used to immobilize the villains who threaten the city. Through the work of a group of Brazilian researchers led by Elíbio Rech at Embrapa [Brazilian Agricultural Research Corporation] Genetic Resources and Biotechnology in Brasília, that fiction could become a reality within a few years, albeit with certain adjustments. Rech heads a team whose objective is to manufacture synthetic fibers inspired by spiderwebs found in Brazilian biodiversity. The laboratory-scale manufacture of this artificial polymer has already been fully mastered, and it could be used as a raw material for making a vast array of products, including biodegradable thread for surgical sutures, bullet-proof vests that are lighter than those currently available, flexible bumpers for automobiles, and even luggage bins and other plastic airplane components. With a little imagination, the synthetic fibers could even be used to create extremely strong ropes capable of uses similar to those employed by Spiderman, the Marvel Comics superhero.
“This new biomaterial, manufactured with the help of tools from biotechnology and genetic engineering, could theoretically be used for an infinite number of applications that require flexibility, strength and biodegradability in a single material,” Rech says. “We have already mastered the technology for producing synthetic spider silk fibers in the lab. Our challenge now is to come up with an economical, fast and safe method for producing it on a large scale.” The research led by Rech began nine years ago, in collaboration with researchers from the University of São Paulo (USP), the Butantan Institute and the University of Brasília (UnB), as well as scientists Randy Lewis of the University of Utah and David Kaplan of Tufts University in the United States.
The interest in producing fibers that mimic spider silk arises from the fact that this material adds unique properties. The filaments spun by spiders are both strong and elastic—steel, in comparison, is extremely strong but inflexible—and they are protein-based and biodegradable. While performing a molecular analysis of this material, the Brazilian scientists discovered that spiders found in Brazilian biodiversity produce extremely robust, flexible silk. “A cable the thickness of a pen spun from spider silk, for example, could be used to move a large, Boeing-type airplane without breaking,” Rech points out. “We know that spider silk has flexibility and strength superior to that of any material in existence, including the polymer Kevlar, which is used to make bullet-proof vests,” notes Rech, who has authored several articles on the topic. The most recent of these articles was published in December 2013 in Nature Communications, a scientific journal from the Nature group.
The published study reveals the complex nanoscale organization of the proteins in spiderwebs found in Brazil. It is that structural organization that lends them their strength and elasticity. The article, coauthored with biologist Luciano Silva, also of Embrapa, reveals the nanostructure of these fibers for the first time. “We used high-resolution atomic force microscopy to amplify the details of each fiber up to one billion times, which enabled us, for example, to differentiate the more elastic fibers from the stronger ones. This research improved and accelerated our mastery of the production of synthetic fibers inspired by spider webs,” Rech explains.
LÉO RAMOSMolecular analyses of spiderwebs found in Brazilian biodiversity will play a role in producing the biopolymerLÉO RAMOS
Programmed biofactories
The process of creating the artificial fibers involves mastering complex techniques used in genetic engineering. The first step in making the biopolymer in the laboratory was to identify and isolate the genes of the silk glands of five spider species (Nephila clavipes, Argiope aurantia, Nephylengys cruentata, Parawixia bistriata and Avicularia juruensis) from three different Brazilian biomes: the Atlantic Forest, Amazonia and the Cerrado. The scientists then performed molecular, biochemical, biophysical and mechanical analyses to study these genes and learn their functions. Based on the results of the analyses, they built synthetic DNA sequences for the production of strong, flexible fibers. The genes modified with the new DNA sequences were subsequently cloned and introduced into the genome of Escherichia coli bacteria, programmed to act as biofactories. As a result, the transgenic E. coli bacteria began a large-scale synthesis of the recombinant proteins that form spider silk fibers, as if they were natural molecule factories. The next step consisted of extracting the proteins from the bacteria. For that purpose, the mass of microorganisms was solubilized (diluted in a liquid medium) and purified in an extraction column, where the proteins were separated from the rest of the material.
The final challenge was to convert the proteins into fiber. In spiders, this process is performed by a special organ called a spinneret, which organizes the proteins in the silk that the spider will use to spin its webs. “What we did was to simulate that organ. With the help of a special syringe that imitates the spinneret, we produced the fibers in the lab from the proteins extracted from the bacteria,” he explains. The process was described in detail in an article in Nature Protocols, another publication of the Nature group, in 2009. The article was authored by Rech, Daniela Bittencourt of Embrapa, and three other researchers from the University of Wyoming.
High cost
According to Rech, besides resulting in applications for several industries, the fact that the studies are based on Brazilian spiders offers the additional advantage of adding value to the nation’s biodiversity. “Sustainability is an important aspect of our work. We study Brazilian biodiversity using recombinant DNA technology as a viable model of choice for creating ‘assets’ and added value,” he says. “The use of synthetic biology and metabolic engineering paves the way for us to engineer organisms, including bacteria, as reactors for producing the proteins associated with the manufacture of spider silk, on a large scale and at an economically viable cost.” That is the greatest challenge for scientists in their efforts to find commercial applications for synthetic fibers and use them to manufacture a wide array of products.
The principal alternative is to discover a “natural factory” that will synthesize the fiber-making proteins on a large scale. The technique that uses bacteria is problematic because of the high cost of the process. As a result, Rech is experimenting with manufacturing the protein in soybean seeds, and Randy Lewis’ group at the University of Utah is doing the same thing with goat’s milk. In each of these systems, the molecule would be extracted at the end of the process and converted into fiber. “Our research is ongoing, and as yet there is no way to estimate how long it will take for the material to become available on the market,” he says.
Research with that same purpose in mind is also being carried out in other countries. A few years ago the US Army, for example, acquired a project created by Canadian laboratories to manufacture synthetic spider silk fibers and look for a way to scale their production. Randy Lewis, in partnership with Rech, is involved in that initiative. “The project is going very well,” says Rech. “But as far as I know, no research group anywhere in the world has yet achieved a low-cost solution. That is what we’re after.”
Scientific articles
SILVA, L.P. e RECH, E.L. Unravelling the biodiversity of nanoscale signatures of spider silk fibres. Nature Communications. Dec. 18, 2013.
TEULÉ, F. et al. A protocol for the production of recombinant spider silk-like proteins for artificial fiber spinning. Nature Protocols. V. 4, No. 3, p. 341-55. 2009.
