The researchers say that the fibres can be recycled quickly (in less than an hour) and repeatedly using a solution of formic acid. The fibres demonstrate tensile strength of approximately 400 MPa. Further, any microparticles released from the fibres during laundering are biodegradable.
Formic-acid solution is an affordable, volatile solvent, which is commonly used to preserve animal feed, in the processing of leather, in traditional textile dyeing and in cleaning. In this case, the solvent breaks-down protein interactions that bind the fibre together without changing the protein itself. Later, the evaporation of the solvent leaves behind raw protein materials that can be used to remake fibres that demonstrate the same mechanical properties.
The researchers take genetic sequences from mussel-foot proteins, spider silk and amyloids (protein aggregations), and blend them together using protein-engineering techniques, so that the strength and recyclability of the resulting material can be controlled independently .
The protein-based material is called silk–amyloid–mussel (SAM) protein hybrid. The protein sequences from mussels help control the materials’ ability to dissolve in formic-acid solution, while the spider-silk and amyloid protein sequences ensure the materials form strong interactions that reform the polymer chains after recycling.
A Professor at Washington university's McKelvey School of Engineering, Fuzhong Zhang, says: “We tune the mussel-foot sequences to make SAM fibres recyclable, while preventing them from shrinking when they get wet.”
The team has demonstrated this process by dissolving and re-making SAM fibres multiple times to create fibres with consistent high strength. Recycled raw proteins can also be repurposed to make adhesive hydrogels for various applications, which can be further recycled to fibres or hydrogels again.
The use of a closed-loop recycling system helps to reduce the cost associated with the use of biomanufacturing processes. Zhang concludes: “Recycling the final product multiple rounds can greatly reduce manufacturing costs over time.”