Researchers are spinning artificial silk from cow milk's whey protein

Scientists spin artificial silk from whey protein fibrils

8:01 AM, 24th January 2017
The hydrodynamic focusing using lateral water jets become entangled the protein fibrils to a microfiber.
The hydrodynamic focusing using lateral water jets become entangled the protein fibrils to a microfiber.

HAMBURG, GERMANY: A Swedish-German research team at Deutsches Elektronen-Synchrotron (DESY) has deciphered a central process for the artificial production of silk. Using intensive X-ray light, the scientists were able to observe how small pieces of protein, so-called fibrils - become knotted in a thread. 

It was found that the longest protein fibrils amazingly are less suitable as starting materials than protein fibrils of poor quality. The team was led by Dr Christofer Lendel and Dr Fredrik Lundell from the Royal Technical College (KTH) Stockholm.

The research is published in the journal Proceedings of the National Academy of Sciences.

Silk is a desirable material with many amazing properties: it is ultralight, more strong than some metal and can be extremely elastic. So far, silk was widely extracted from cultured caterpillars. 

“Many research groups around the world work to produce silk artificially. Such a material could also be modified in such a way that it has new properties, for example for biosensors or self-resolving wound dressings,” emphasised co-author Prof Stephan Roth of DESY, the adjunct professor at KTH Stockholm.

It is mostly difficult to imitate nature in this case. The Swedish team depends on self-assembly of the biological raw material.

"This is a very simple process. Some proteins form nanofibrils by themselves under the right environmental conditions. These protein fibrils are then pressed in a carrier fluid through a channel in which they are densified with additional lateral water jets to form a fibre," said Lundell.

"The researchers call the latter process hydrodynamic focusing. In this way, a team around Lundell had already made artificial wood fibres from cellulose fibres. In fact, the process has some similarity with the way spiders make their silk,” added Lendel.

In the new study, researchers used a whey protein, which forms nanofibrils under the effect of heat and acid. The longest and thickest fibrils are found in the solution at a protein concentration of less than four percent. They are on average about 2000 nanometers long and 4 to 7 nanometers thick. 

With a protein concentration of more than six percent in the solution, the fibrils remain significantly shorter with an average of 40 nanometers and are only 2 to 3 nanometers thick. Moreover, they are worm-like curved instead of straight and 15 to 25 times softer than the long fibrils.

In the lab, though, it was found that the long, straight fibrils produced poorer fibres than those of the short, curved ones. With DESY's extremely bright X-ray source PETRA III, researchers have now been able to explore why this is so. 

"The crooked nanofibrils are much better than the straight ones. In the X-ray image, the structure of the curved fibrils is also retained in the finished fibre,” said co-author Roth, who heads the DESY measuring station P03, where the experiments were carried out.

"The strongest fibres are created by a stable balance between an ordered nanostructure of the material and an interlacing of the fibrils," added Lendel. 

"Natural silk has an even more complex structure of evolutionarily enhanced proteins. They fit together so that there are both regions with a strong order, so-called beta sheets that give strength to the fibre as well as low-order regions that give flexibility to the fibre. But, the fibre structures of artificial and natural silk differ significantly. Especially, the protein chains have in natural silk, a greater number of intermolecular interactions that link the proteins and lead to a stronger fibre," continued Lendel.

In the experiments originated about five millimetres long silk fibres of medium quality. "We used the whey protein to understand the underlying principle. The entire process can now be optimised to produce fibres with better or tailor-made properties," concluded Lendel.

The findings could also be used to develop other materials with novel properties, such as artificial tissue for medicine.

© DESY News

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