Spider silk has been the focus of many materials science investigations over the years. Its strength "pound-for-pound" when compared with steel is astonishing. Unfortunately, some of its other characteristics make it untenable as a practical material for engineering and other applications. But, what if we splice in some wood fibers? That is what Mark Linder and his colleagues Aalto University reasoned might be a useful proposition.
As part of the work undertaken at the Centre of Excellence in Molecular Engineering of Biosynthetic Hybrid Materials (HYBER), the team has created a new bio-based composite material from cellulose fibers and spider silk proteins . The resulting strong and resilient material could displace synthetic polymers in a wide range of products from medical applications, such as surgical fibers to textiles for industry and packaging.
Linder suggests that nature offers an excellent list of ingredients for the development of novel materials and biomimetics. Stiffness, toughness, flexibility, extensibility are all there in the natural repertoire. For cellulose and spider silk, the biggest advantage for the modern world might be that unlike synthetic polymers, these materials would be entirely biodegradable. As such, these composites will not generate tiny persistent particles and fibers in the way that synthetic fibers do, and so should have none of the polluting and harmful effects of so-called micro-plastics.
"Our researchers just need to be able to reproduce the natural properties," explains Linder. The team used pulp from birch trees and broke it down into cellulose nanofibrils. They could then aligne these fibers using a stiff scaffold. In parallel, they infiltrated the network of cellulose nanofibrils with an adhesive matrix of soft and energy-dissipating spider silk produced by genetically modified bacteria in the laboratory.
"Because we know the structure of the DNA, we can copy it and use this to manufacture silk protein molecules which are chemically similar to those found in spider web threads," Linder explains. "The DNA has all this information contained in it." Using this approach to generate "spider silk" rather than living spiders means they can make more of the protein, faster, and also have the potential to tweak the DNA to change the protein chains subtly, to perhaps even build on or enhance natural spider silk.
"Our work illustrates the new and versatile possibilities for protein engineering. In the future, we could manufacture similar composites with slightly different building blocks and achieve a different set of characteristics for other applications," explains research collaborator Pezhman Mohammadi of VTT Technical Research Centre of Finland."Currently, we are working on making new composite materials as implants, impact resistance objects, and other products."