Unraveling the Secrets of Spider Silk
Discover how advanced microscopy is helping to reveal new insights into spider silk.
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Spider silk is a remarkable natural material that has captured the imagination of a group of scientists who are currently exploring its untapped potential in medical and materials science. Its high tensile strength, natural elasticity and environmentally-friendly properties offer exciting advantages in the fields of regenerative medicine and high-performance fabrics, and are positioning spider silk as a material to watch.
The Anna Rising group at Stockholm’s largest university is looking into the potential of synthesizing spider silk at scale, using advanced microscopy to improve understanding of its properties and performance.
Successful synthesis
To produce spider silk at a scale suitable for commercial use, it must be synthesized. There are two simple reasons for this: firstly, spiders are naturally small and cannibalistic and secondly, spiders produce significantly less silk than silkworms and other producers of natural fibers.
Major ampullate silk is of particular interest to researchers. This type of silk, which is used to construct the rim and spokes of a web, has a similar tensile strength to steel of approximately 1.5 GPa but a much lower density of 1.3 g/cm3. And unlike steel, this type of silk can stretch by up to 30% without breaking.
The unique properties of spider silk are due to proteins called spidroins. Spidroins have a repetitive amino acid structure with segments that fold into “crystalline” regions, while other segments possess unstructured protein chains to deliver the characteristic stretchy, thin line of silk that is as strong as steel. By understanding the effect of lowering the pH on the spidroin protein structure, researchers are able to determine how spider anatomy facilitates silk formation, which in turn allows them to replicate this mechanism and generate impressive lengths of synthetic spider silk.1
The artificial production of spidroins is achieved by inserting the redesigned genetic coding for the protein into microorganisms such as Escherichia coli (E. coli). This process allows researchers to produce large amounts of spidroins, with one liter of bacterial culture yielding tens of kilometers of artificial spider silk.2 Even more impressive than the scale, is the fact that downstream processing of the proteins only requires water-based methods and a simple change of pH for silk spinning. This biomimetic process removes the need for organic solvents, which makes it far better suited to scale up for industrial production both from an economical and environmental perspective.3
Under the microscope
Microscopy techniques allow the researchers to examine spider silk in detail, and closely monitor any micro-scale changes to the material while undergoing tensile and environmental testing. As well as revealing the properties of natural spider silk, microscopy techniques also allow researchers to monitor any differences in performance in synthetically produced spider silk.
Custom microscopy stages have enabled testing under a variety of controlled environmental conditions, to ensure that the synthetic silk is performing as expected and identify whether any change is needed to maintain performance.
In terms of mechanical design, testing 1 cm lengths of filament demands a custom-built solution. The bespoke microscopy stage used by the Anna Rising group features grips that have been designed specifically to accommodate the 1 cm lengths of filament used across its research. Because such short lengths would not fit on a standard industrial tensile tester, customized extender units have been designed to fit these filaments within an environmental chamber to ensure no loss of performance during the test cycle.
Customized microscopy solutions allow the team in Stockholm to better understand the properties of synthetic spider silk and the performance of the material under different conditions by monitoring the effects of temperature and humidity on the fibers. Real-time monitoring enables the team to improve their understanding of the structure-function relationships within spider silk, and how the protein sequence and spinning conditions translate to mechanical properties and performance.
By using the custom system alongside analytical techniques such as bright-field microscopy and polarized light microscopy, the team can determine fiber diameter and behavior during stretching, providing valuable insights into how the molecular alignment relates to fiber strength.
These detailed insights into fiber performance under changing conditions mean that the researchers are well placed to take their research to the next level – applying these findings to real-world applications.
Early applications
While there seems no shortage of possibilities for synthetic spider silk, the team is currently focusing its attention on technical application. Multi-filament yarn is being benchmarked against known fibers, to assess suitability for applications including healthcare, performance clothing, and shock absorbers for robotics and aerospace.
As the threads have the potential to replace plastic-based fibers, synthetic spider silk may present a strong opportunity for the textiles industry to reduce its environmental impact. Currently, 67% of fibers contribute significantly to environmental concerns4 such as CO2 emissions and non-biodegradable plastic waste filling oceans and landfill. As a sustainable, biocompatible option, spider silk shows considerable promise.
The team is particularly excited about the clinical applications of spider silk. Early animal studies show that natural spider silk can assist in regrowing nerve fibers to span a gap of 6 cm without triggering a major immune response,5 and the team is taking this to the next level by investigating the potential of spider silk in bone and tissue regeneration. Work has already been done by culturing a large number of human stem cells onto “scaffolds” of spider silk fibers, which has been a huge success.6 However, as the biomedical industry is heavily regulated, and extensive testing is required to provide data suitable for regulatory scrutiny, the team is taking the long-term view.
The future is spider silk
The unique combination of spider silk’s strength with extensibility in a lightweight, biodegradable and biocompatible format makes it unlike any other material available today. As the Anna Rising group continues to develop its understanding of this unique material, synthetic spider silk is set to fulfill its true potential.
About the authors:
Dr. Benjamin Schmuck is a postdoctoral researcher in the Anna Rising Group.
Clara Ko is sales and marketing director at Linkam Scientific Instruments.
