Spider silk is one of the wonder materials of nature. It is strong, light, supple, and biodegradable yet stronger than steel.
The slender silk spun by spiders is 30 times thinner than a human hair yet harder than the synthetic fiber used in making the bullet-proof vest, known as Kevlar.
Making artificial spider silk has been a failure for many reasons including use of harsh chemicals and resulting fibers not finding any wider use.
However, there is good news now. Researchers at the Swedish University of Agricultural Sciences and Karolinska Institutet have reported success in producing kilometer-long spider silk threads for the first time resembling the original spider silk.
The results of the experiment have been published in the journal Nature Chemical Biology.
Overcoming The Challenge
The dream of mass production of spider silk remains a chimera. The challenges include the difficulty in farming carnivorous spiders and raising them in bulk.
Technically, synthetic production means handling the complexity and size of protein molecules in silk called "spidroins" which are hard to work with.
"In general, the larger the protein, the more difficult it can be to produce, and spider silk happens to be a very large protein, often in the range of 3,000 amino acids," noted Daniel Meyer, marketing executive of biotech company Spiber.
According to the Swedish researchers, the challenges of artificial spider silk production were compounded by the difficulties in getting silk proteins that are soluble in water along with the absence of sustained sources like bacteria. In spiders, silk remains stored in their glands as an aqueous solution before they get converted into the fiber.
Manipulation Of pH Gradient
The Swedish researchers set their focus on the critical pH gradient existing in the spider's silk gland. The success of researchers came from replicating the natural process into a biomimetic spider silk spinning.
The team had Anna Rising, Jan Johansson, and Marlene Andersson from the Swedish University of Agricultural Sciences and Karolinska Institutet.
"We designed a process that recapitulates many of the complex molecular mechanisms of native silk spinning. In the future this may allow industrial production of artificial spider silk for biomaterial applications or for the manufacture of advanced textiles," said Anna Rising.
The scientists put to use the same pH variation in their artificial spider silk protein sourced from bacteria but made sure the production process was quantifiable.
The proteins they used came from E.coli bacteria.
Mimicking the spider silk gland, the biomimetic spinning apparatus could spin kilometer-long fibers by lowering the pH of the artificial aqueous spider silk protein.
"To our surprise, this artificial protein is as water soluble as the natural spider silk proteins, which means that it is possible to keep the proteins soluble at extreme concentrations," added Rising.
"This allowed us for the first time to spin artificial spider silk without using harsh chemicals," said the study's co-author Jan Johansson.
"The high amounts of proteins produced in bacteria allow us to spin a kilometer of the biomimetic fibers from just one liter of E.coli culture," he added.
The team also highlighted the possible applications of artificial spider silk, such as bio-compatible threads in regenerative medicine; repair of the spinal cord; and growing stem cells to repair damaged hearts.