Programmable Proton Conduction in Stretchable and Self-Healing Proteins

Proton conduction is ubiquitous in nature and has many applications in energy and electronic technologies. Although protein based materials show bulk proton conduction 10 times lower than conventional ion-conducting materials, they have unique advantages including biocompatibility, self-healing, tunable structure, and fine-grained control of material properties via amino acid sequence. Here, we studied the bulk proton conduction of tandem repeat proteins and demonstrate that tandem repetition of sequences from squid ring teeth (SRT) proteins significantly and systematically enhances bulk proton transport properties. Inelastic neutron scattering experiments between 4 K and 350 K reveal that highly repetitive proteins show enhanced conductivity. Our highly repetitive proteins achieve higher proton conductivity than state-of-the-art biological proton conductors (with peak conductivities of 3.5 mS cm^-1), as well as demonstrate unique self-healing characteristics. These proteins also exhibit exceptionally high stretching (-300%) relative to proton conductive materials while maintaining their high strength, offering the unique possibility of dynamic responsivity to strain. Programming physical properties through tandem repetition introduces a new approach for understanding proton conductivity and enhancing the transport properties of synthetic proteins.