Fuzhong Zhang, professor of energy, environmental and chemical engineering. Photo: Washington University in St. Louis.
Fuzhong Zhang, professor of energy, environmental and chemical engineering. Photo: Washington University in St. Louis.

Scientists have long been intrigued by the remarkable properties of spider silk, which is stronger than steel yet incredibly lightweight and flexible. Now, Fuzhong Zhang, a professor of energy, environmental and chemical engineering in the McKelvey School of Engineering at Washington University in St. Louis, has made a significant breakthrough in the fabrication of synthetic spider silk, paving the way for a new era of sustainable clothing production.

Since engineering recombinant spider silk in 2018 using bacteria, Zhang has been working to increase the yield of silk threads produced by microbes while maintaining the desirable properties of enhanced strength and toughness.

Higher yields will be critical if synthetic silk is to be used in everyday applications, particularly in the fashion industry. Here, renewable materials are much in demand to stem the environmental impacts that come from producing an estimated 100 billion garments and 92 million tons of waste each year.

With help from an engineered mussel foot protein, Zhang has created new spider silk fusion proteins called bi-terminal Mfp fused silks (btMSilks). Compared with recombinant silk proteins, btMSilk fibers have substantially improved strength and toughness while still being lightweight, and microbes can produce them with eightfold higher yields. This could revolutionize clothing manufacturing by providing a more eco-friendly alternative to traditional textiles. Zhang and his colleagues report their work in a paper in Nature Communications.

“The outstanding mechanical properties of natural spider silk come from its very large and repetitive protein sequence,” Zhang said. “However, it is extremely challenging to ask fast-growing bacteria to produce a lot of repetitive proteins.

“To solve this problem, we needed a different strategy. We went looking for disordered proteins that can be genetically fused to silk fragments to promote molecular interaction, so that strong fibers can be made without using large repetitive proteins. And we actually found them right here in work we’ve already been doing on mussel foot proteins.”

Mussels secrete specialized proteins on their feet to allow them to stick to things, and Zhang and his collaborators had engineered bacteria to produce these proteins for use as adhesives in biomedical applications. As it turns out, mussel foot proteins are also cohesive, allowing them to stick to each other. By placing mussel foot protein fragments at the ends of the synthetic silk protein sequences, Zhang was able to create a less repetitive lightweight material that’s at least twice as strong as recombinant spider silk.

The yields of Zhang’s material increased eightfold compared with past studies, reaching eight grams of fiber material from each liter of bacterial culture. This output constitutes enough material for testing in real products.

“The beauty of synthetic biology is that we have lots of space to explore,” Zhang said. “We can cut and paste sequences from various natural proteins and test these designs in the lab for new properties and functions. This makes synthetic biology materials much more versatile than traditional petroleum-based materials.”

In coming work, Zhang and his team plan to expand the tunable properties of their synthetic silk fibers to meet the exact needs of each specialized market.

“Because our synthetic silk is made from cheap feedstock using engineered bacteria, it presents a renewable and biodegradable replacement for petroleum-derived fiber materials like nylon and polyester,” Zhang said.

This story is adapted from material from the Washington University in St. Louis, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.