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Scientists have long envied the lowly silkworm's ability to spin the strongest natural fiber known to man. Now they are one step closer to understanding just how the creature manages the feat. In a paper published today in the journal Nature, researchers reveal that the key lies in the animal's ability to carefully control the water content in its silk glands. The findings should help improve future artificial silk-making techniques.
Scientists have known for some time that silk's impressive strengths arise from a mix of proteins with various properties. Some, for example, are hydrophilic (water loving), whereas others are hydrophobic (water fearing). But just how silkworms and spiders can convert solutions containing these compounds into silk threads without clogging their silk glands was unclear. In the new work, David L. Kaplan and Hyoung-Joon Jin of Tufts University dissolved silk from a cocoon and removed the compounds responsible for gluing the fibers together. They then examined how the remaining proteins behaved in the presence of various amounts of water. They found that as the water level lowered, tiny islands of solid proteins began to form. As more water was removed, these so-called micelles joined together to form larger gel-like structures ranging between 100 and 200 nanometers in diameter. This aggregation allows the proteins to stay soluble and avoid premature crystallization.
If the proteins were to become solid too soon in silk-producing animals, they could permanently block the spinning system, with potentially fatal results. According to the report, the silk proteins fold in on themselves and arrange their hydrophobic and hydrophilic parts such that they remain soluble prior to being spun. Notes Kaplan, "this finding could lead to the development of processing methods resulting in new high-strength and high-performance materials used for biomedical applications, and protective apparel for military and police forces."