Modulating the Properties of Functional Biocomposites with Engineered Bacterial Protein Fibers

Protein-based materials can be genetically customized for a range of applications. In addition to displaying biocompatibility, tunable bioactivity and responsiveness, they represent sustainable alternatives to conventional synthetic polymers. In particular, proteins that self-assemble into higher order structures and can be produced at large scale are of interest for deployment into wearable devices and alternatives for commodity materials like plastics, textiles and electronics. Curli fibers produced as part of the extracellular matrix of <i>Escherichia coli</i> bacteria represent a promising protein scaffold, due to their unique physicochemical properties, including their ability to self-repair and their resistance to harsh conditions. Once secreted by bacterial cells, CsgA subunits, the self-assembling repeats of curli fibers, form fibrous structures that can further aggregate, entangle, and gel into macroscopic materials. Among other functionalities, we have genetically encoded in CsgA the ability to fluoresce, to conduct charges, and to respond to stimuli.<br/><br/>Here, I will present an overview of advances that we have made to engineer biocomposite materials containing functional curli fibers. The fibers allow to modulate the mechanical, electrical, self-healing and sensing properties of the composites. First, I will highlight the scalable and simple bioprocesses that we have developed to express, extracellularly secrete, and isolate genetically engineered curli fibers. Then, I will present two main applications of biofunctionalized composites: 1) a curli fiber – conductive polymer composite that exhibits self-healing properties and tunable electrical conductivity dependent on the protein content, and 2) a “living” self-repairing biofilm-based textile in which the curli fibers part of the biofilm’s extracellular matrix act as glue to repair the textile via a water-induced healing mechanism. So far, we have applied curli-functionalized textiles to the fabrication of sweat pH sensors and we foresee several applications of curli-based composites for wearable devices and biocompatible electrodes. These devices enable novel functions that can only be achieved by biological materials, and bring us closer to a bio-based economy.