Stronger than steel, tougher than Kevlar. No, it isn’t the latest superhero from DC or Marvel, but reference to a new material produced from microorganisms – a type of super-strong variant of spider silk. This represents a step-forward in both materials science and bioengineering.
The development in bio-fabrics comes from the Washington University in St. Louis. Looking for inspiration for a new material, the researchers turned their attention to spider silk. The reason for the consideration of arachnid spun material was because the silk is one of the strongest, toughest materials on the Earth.
To replicate the properties of spider silk, the scientists constructed amyloid silk hybrid proteins and produced them in engineered bacteria. The resulting fibers have been demonstrated to be stronger and tougher than some types of natural spider silks.
The scientific method behind the research involved a modified the amino acid sequence of spider silk proteins. Here, new properties could be introduced and some of the attractive features of spider silk retained.
The main complexity with the development was with creating β-nanocrystals. These are a main component of natural spider silk, and the factor that mostly contributes to its strength. To overcome this, the research team found a means to redesign the silk sequence. This was by introducing amyloid sequences that have high tendency to form β-nanocrystals. The resulting proteins had less repetitive amino acid sequences than spider silk.
The simpler amino acid sequence was also important for making the material easier to be produced by engineered bacteria. The new material has been named “polymeric amyloid” fiber.
It was also found that the longer the protein, the stronger and tougher the resulting fiber. The researchers produced 128-repeat proteins. In testing out this fiber, it was found that the material had gigapascal strength (this is a measure of how much force is needed to break a fiber of fixed diameter).
The resultant material was found to be stronger than common steel. In addition, the fibers’ toughness (that is, a measure of how much energy is needed to break a fiber) was measured to be greater than Kevlar. Rigid spider silk has a toughness factor of 180 megajoules/meter compared to Kelvar’s toughness factor of 50 megajoules/meter.
The research is continuing and three of thousands of different amyloid sequences remain to be examined, and these could enhance the properties of the material still further. The macroscopic amyloid fibers will enable a wide range of mechanically demanding applications to be produced.
The ultimate goal is to engineer high-performance materials. The research appears in the journal ACS Nano, titled “Microbially Synthesized Polymeric Amyloid Fiber Promotes β-Nanocrystal Formation and Displays Gigapascal Tensile Strength.”
