Scientists have developed a method to pull silk fibres from a silk protein liquid made by genetically engineered E. coli. A researcher says that the method is one step closer to being able to make artificial spider silk.
Spider silk is a unique natural material that has sparked keen interest from researchers for many years because of its incredible flexibility and enormous strength.
Imagine a sweater spun from spider silk being both flexible and soft and having the strength of a bulletproof vest.
Even a very thin spider silk rope would be very difficult to destroy.
Since extracting the spider silk from the spiders themselves is not practically possible, researchers have tried to figure out how to do this in the laboratory.
They have now developed a method to get E. coli to make spider silk proteins and get a robotic device to pull and analyse the silk fibres from the purified silk solution.
“We can now make long sections of the fibres, which was not possible before. We can also measure the strength of the silk when we pull on it, and this will make our attempts to make artificial spider silk much easier,” explains a researcher behind the study, Teemu Välisalmi, Postdoctoral Researcher, Department of Bioproducts and Biosystems, Aalto University, Espoo, Finland.
The research has been published in the International Journal of Biological Macromolecules.
E. coli producing silk proteins
The researchers modified E. coli with the gene for spider silk protein, enabling them to produce and store the spider silk protein if they are fed the correct substrate.
Through various purification steps, the researchers can both analyse and extract the silk proteins from the aqueous solution, even though the individual silk fibres are so thin that seeing them with the naked eye is almost impossible.
Teemu Välisalmi explains that silk cannot yet be made in the same way as the spiders, adding that:
“Spider silk is formed in long continuous chains, and E. coli have great difficulty in processing the complex genetic information found in natural silk proteins. We have therefore taken only part of the synthesis route to create something that the E. coli can produce. Spider silk also comprises several long proteins, but so far we can only get our E. coli to produce one of the proteins and only in a short version. However, this is a step on the way to being able to make real spider silk in the laboratory.”
Robotic device pulls silk proteins from an aqueous solution
The researchers developed a mechanical method to pull silk threads out of the solution containing silk proteins while being able to measure the tensile strength of the threads.
Teemu Välisalmi explains that silk can be extracted from a solution in different ways. One way is to inject the solution with silk proteins into another liquid, which causes the silk proteins to coagulate. However, this does not produce uniformity in the fibres, which is a useful characteristic.
The researchers therefore wanted to develop a new method to pull the silk fibres directly out of the liquid.
Their method comprises a mechanical device with the liquid containing silk proteins in a needle and a robotic arm that slowly pulls the silk out of the liquid. The silk proteins solidify when exposed to air, enabling the researchers to continue pulling one silk protein after another from the liquid in one long fibre.
The device also has a sensor that can measure the strength of the silk thread and a camera that films the silk threads as they emerge from the liquid.
“This means that we can study the silk thread while it is being pulled out of the liquid. We can both see it and measure its tensile strength,” explains Teemu Välisalmi.
Useful for other types of silk
Teemu Välisalmi says that the development of the new method enabled researchers to demonstrate the importance of liquid-to-liquid phase separation in artificial spider silk for the first time.
Since the researchers can also film the proteins as they form strong fibres, the method is suitable for studying the properties of both artificial spider silk and many other types of artificial silk.
For example, the researchers have also used the method to study artificial silk from silkworms.
“Part of the goal of this research was to develop a method that makes studying silk proteins in general much easier. This will encourage research in the field and bring us a step closer to being able to make true-to-life silk with E. coli,” concludes Teemu Välisalmi.
