Along with its use in clothing, silk also shows promise for use in products ranging from surgical sutures to seed coverings. Scientists have recently devised a method of making the material stronger, by altering the diet of silkworms.
In the wild, silkworms feed on mulberry leaves. Nutrients from those leaves are absorbed by the bloodstream and passed into modified salivary glands, from which the worms draw their cocoon-forming stands of silk. Researchers at Japan's Tohoku University have replaced the mulberry leaves with an existing commercial silkworm feed, to which they added cellulose nanofibers (CNFs).
These tiny fibers are produced from cellulose-containing natural materials such as wood waste. If prepared correctly, the resulting CNFs can be incorporated into building materials that are one-fifth the weight of steel, yet fives times as strong. One challenge, however, lies in getting the nanofibers to align themselves properly.
After ingesting the augmented feed, silkworms dispersed the CNFs in their saliva as they were producing silk strands. Importantly, the nanofibers were all oriented in the direction of the saliva flow, which proved to be ideal for strengthening the silk. In fact, when the enhanced silk strands were tested, they were found to be twice as strong as strands produced by worms that weren't fed any of the nanonofibers.
It should be noted that several years ago, Chinese scientists were likewise able to strengthen silk by adding graphene and carbon nanotubes to the diet of silkworms.
The more recent Japanese research is described in a paper that was recently published in the journal Materials & Design.
Source: Tohoku University
