Graphene-fed silkworms produce super-silk
Image credit: Fastily at en.wikipedia
Silkworms fed mulberry leaves sprayed with graphene or carbon nanotubes produced super-strong carbon-enhanced fibres in an experiment by Chinese researchers.
The team from Tsinghua University led by Yingying Zhang used a silk production method that has been standard since ancient times, which involves cultivating silkworms on mulberry leaves and harvesting their cocoons once the worms start pupating. The cocoons are subsequently dissolved in water to extract individual fibres, which are then spun into a reel.
The only difference in the 5,000-year old production technique was spraying the leaves with a liquid containing 0.2 per cent of graphene or carbon nanotubes.
After collecting the cocoons, the researchers found that while the worms excreted a portion of the carbon nanomaterial, part of it got incorporated into the silk fibres.
The researchers said that trying to reinforce already spun silk would be much more complicated as it would require dissolving the nanomaterials in toxic chemical solvents and applying those to the silk.
The team believes their method is both extremely environmentally friendly and suitable for large-scale commercial super-silk production. Such a material could be used for manufacture of durable protective fabrics, biodegradable medical implants or eco-friendly wearable electronics.
In experiments, silk from the carbon-fed worms was able to withstand 50 per cent higher loads than conventional silk. Heating the fibres to 1050°C, which led to the carbonisation of the silk protein, showed that the graphene-enhanced silk is electrically conductive - something that ordinary silk is not.
Raman spectroscopy and electron microscopy imaging showed that the carbon-enhanced silk fibres had a more ordered crystal structure due to the incorporated nanomaterials.
The researchers are not entirely sure how the silkworms, which spin the fibres from a solution of silk protein produced in their salivary glands, incorporate the carbon nanomaterials into the silk.