Spider silk, wood combination replicates material advantages of plastic

By combining the silk protein from spider web threads with wood cellulose fibers, scientists have created a material featuring strength and extensibility comparable to plastic.

Extensibility is the extent to which a material can be stretched without causing it to tear or break, and until now, scientists have struggled to pair the material property with strength.

To overcome the challenge, scientists turned to two biological ingredients with the target qualities. Cellulose is know for its strength, while the silk threads produced by spiders offer impressive extensibility.

"We used birch tree pulp, broke it down to cellulose nanofibrils and aligned them into a stiff scaffold," Pezhman Mohammadi, researcher at the VTT Technical Research Center of Finland, said in a news release. "At the same time, we infiltrated the cellulosic network with a soft and energy dissipating spider silk adhesive matrix."

Mohammadi worked with scientists at Aalto University to produce the bio-based composite material.

Though silk is produced by silk worms and spiders, scientists at Aalto sourced the silk from bacteria augmented with synthetic DNA.

"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," said Markus Linder, a professor at Aalto. "The DNA has all this information contained in it."

The production process yielded a material with high strength and stiffness, as well as increased toughness. Most importantly, this strength is not compromised when the material is stretched.

Researchers described their new material in the journal Science Advances. The material's qualities are similar to those of plastic, but because it is biodegradable, the new material is more eco-friendly.

"Our work illustrates the new and versatile possibilities of protein engineering. In future, we could manufacture similar composites with slightly different building blocks and achieve a different set of characteristics for other applications," Pezhman said. "Currently we are working on making new composite materials as implants, impact resistance objects and other products."

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