More Than a Spider Can Do
Engineers who would like to ___ 31 ___ the accumulated evolutionary wisdom embodied in biological materials are fascinated by silk – particularly spider silk. Strands of it are stronger than steel, yet they are able to stretch by 40 % of their length before they break. Silk also comes in a variety of forms; the radial strands of a web, for example, have a different composition from the circumferential ones because the stresses and strains on them are different.
The problem with the products of evolution, ___ 32 ___, is that they are honed to do jobs for the creatures they come from, not for humanity. So further engineering is needed to turn them into useful materials. And that is what David Kaplan and his colleagues at Tufts University have been trying to do. ___ 33 ___ studies have identified the sequences of DNA within genes for spider silk proteins that result in the different properties of the final product. The most important properties are hydrophilia (a tendency to interact with water), hydrophobia (a tendency to shun it) and the ability to link up spontaneously with other proteins and thus form larger, more ___ 34 ___ structures. Starting with this parts list, Dr Kaplan wondered if he could extend the range of properties of the resulting silk beyond those found in nature. He has discovered that he can.
In particular, the researchers found that structures which would have remained thin and film-like in normal spider silk thickened into tiny fibres and spheres in propanol. Some of the tougher and more water-resistant forms of silk might be employed to impregnate synthetic fibres and lightweight materials called hydrogels, in order to make them stronger and more waterproof. The more resilient materials that resulted could then be used to coat and toughen surfaces, strengthen the biologically friendly plastics employed in surgery, and create strong lightweight components for use in aircraft, where weight is at a premium. If all goes well, then, a useful new ___ 35 ___ of polymers looks ready to be spun.
The Economist