The hair-like fiber pictured here is a sample of SAM, silk-amyloid-mussel protein hybrid, an engineered protein polymer that can be easily recycled and reused when dropped in a solvent.
Photo Credit: McKelvey School of Engineering
Scientific Frontline: Extended "At a Glance" Summary: Engineered Protein Fibers (SAM)
The Core Concept: Silk-amyloid-mussel (SAM) protein hybrids are bioengineered materials produced by genetically modified microbes that serve as a fully recyclable, biodegradable alternative to synthetic textiles.
Key Distinction/Mechanism: Unlike petrochemical plastics that degrade in quality during recycling, SAM fibers dissolve rapidly in a formic acid solvent, breaking the structural bonds without altering the underlying proteins. Once the solvent evaporates, the raw proteins can be reconstituted into fibers with their original strength.
Major Frameworks/Components:
- Genetically Engineered Microbes: Utilized within bioreactors to synthesize the raw protein polymers.
- Mussel Foot Proteins: Genetic sequences integrated to control solubility in formic acid and prevent the material from shrinking when exposed to water.
- Spider Silk and Amyloids: Protein sequences that provide high tensile strength and ensure the polymer chains reconnect robustly after the recycling process.
- Formic Acid Solvent: A volatile, industry-standard solution used to safely dissolve the fibers for closed-loop recycling.
Branch of Science: Synthetic Biology, Materials Science, Environmental Engineering.
Future Application: The development of a closed-loop recycling system for commercial textiles and the creation of repurposable adhesive hydrogels, ultimately lowering biomanufacturing costs.
Why It Matters: The textile industry is a dominant source of global waste and aquatic microplastics. Implementing biodegradable, infinitely recyclable protein fibers prevents the persistent environmental contamination caused by traditional synthetic shedding during wash cycles.
The textile industry produces a substantial portion of the world’s waste, with only about 12% of fiber materials ending up in recycling. Textiles also account for much of the microplastics in oceans. During every wash cycle, synthetic fibers shed microplastics that are flushed down the drain and eventually enter aquatic environments. Increasing textile recycling alone will not solve this problem because most petrochemical-based fibers are difficult to recycle and continue to release persistent microplastics throughout their life cycles.
Engineers from Washington University in St. Louis may have a solution, thanks to dedicated synthetic biology work in the lab of Fuzhong Zhang, the Francis F. Ahmann Professor in the Department of Energy, Environmental and Chemical Engineering in the McKelvey School of Engineering and co-director of the Synthetic Biology Manufacturing of Advanced Materials Research Center (SMARC).
The results of that work, recently published in the journal Advanced Materials, detail the creation of protein-based materials produced in bioreactors using genetically engineered microbes. These materials can be readily recycled after use and remade into the same fibers over multiple cycles. In addition, any microparticles released from these fibers during washing would be biodegradable.
“We engineered recyclable protein fibers that dissolve in a formic acid solution within seconds, yet remain stable in water and strong after drying,” Zhang said.
A formic acid solution is an affordable, volatile solvent commonly used in industry for animal feed preservation, leather processing, traditional textile dyeing, cleaning, and many other processes. In this case, the solvent breaks down the protein interactions that bind the fiber together without changing the protein itself. Later, solvent evaporation leaves behind raw protein materials that can be used to remake fibers of the original strength and properties.
The recycling industry has long struggled to make plastic reuse more practical and cost-effective. Plastics can be melted and remolded, but the recycled plastics are often weaker, especially when they contain additives or contaminants. Other recycling methods break the chemical bonds within polymers and then rebuild them through resynthesis, but this process can substantially increase costs and emissions. In general, the stronger a material is, the harder it is to recycle, because the same bonds that give the material its strength must often be broken during recycling.
To solve this problem, the team drew inspiration from nature. They took genetic sequences from mussel foot proteins, spider silk, and amyloids (protein aggregations) and knitted them together using sophisticated protein engineering techniques, enabling the independent control of the strength and recyclability of the resulting material.
Their protein-based material is called SAM, a silk-amyloid-mussel protein hybrid. The adhesive protein sequences from mussels help control the material’s ability to dissolve in a formic acid solution. The spider silk and amyloid protein sequences ensure the material forms strong interactions that reconnect the polymer chains after recycling.
“We tune the mussel foot sequences to make SAM fibers recyclable while preventing them from shrinking when they get wet,” Zhang said.
The team demonstrated this process by dissolving and remaking SAM fibers multiple times, producing fibers with consistently high strength. Recycled raw proteins can also be repurposed to make adhesive hydrogels for various applications, which can then be further recycled into fibers or hydrogels.
Achieving a closed-loop recycling system also helps reduce the cost of these materials. Biomanufacturing is expensive, so researchers have often been limited to targeting luxury applications. However, with a circular system of resources, biomanufacturing costs begin to decrease drastically.
“Recycling the final product through multiple rounds can greatly reduce manufacturing costs over time.”
Reference material: What Is: Synthetic Biology
Funding: This research was funded by the United States Department of Agriculture (grant number 20196702129943 to F.Z.) and the National Science Foundation (DMR-2105150, DMR-2207879, and OIA-2219142 to F.Z.). This research utilized mass spectrometry resources at the Washington University Biomedical Mass Spectrometry Resource, which is supported by National Institutes of Health grant 8P41GM103422.
Published in journal: Advanced Materials
Title: Synthetic biology leads to recyclable textiles: Engineered protein fibers for a cleaner future
Authors: Jingyao Li, Juya Jeon, Kok Zhi Lee, and Fuzhong Zhang
Source/Credit: McKelvey School of Engineering
Reference Number: sybi051026_01