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

Mechanical Properties of Tandem-Repeat Proteins Are Governed by Network Defects

Topological defects in highly repetitive structural proteins strongly affect their mechanical properties. However, there are no universal rules for structure–property prediction in structural proteins due to high diversity in their repetitive modules. Here, we studied the mechanical properties of tandem-repeat proteins inspired by squid ring teeth proteins using rheology and tensile experiments as well as spectroscopic and X-ray techniques. We also developed a network model based on entropic elasticity to predict structure–property relationships for these proteins. We demonstrated that shear modulus, elastic modulus, and toughness scale inversely with the number of repeats in these proteins. Through optimization of structural repeats, we obtained highly efficient protein network topologies with 42 MJ/m³ ultimate toughness that are capable of withstanding deformations up to 350% when hydrated. Investigation of topological network defects in structural proteins will improve the prediction of mechanical properties for designing novel protein-based materials

Self-Healing Textile: Enzyme Encapsulated Layer-by-Layer Structural Proteins

Self-healing materials, which enable an autonomous repair response to damage, are highly desirable for the long-term reliability of woven or nonwoven textiles. Polyelectrolyte layer-by-layer (LbL) films are of considerable interest as self-healing coatings due to the mobility of the components comprising the film. In this work mechanically stable self-healing films were fabricated through construction of a polyelectrolyte LbL film containing squid ring teeth (SRT) proteins. SRTs are structural proteins with unique self-healing properties and high elastic modulus in both dry and wet conditions (>2 GPa) due to their semicrystalline architecture. We demonstrate LbL construction of multilayers containing native and recombinant SRT proteins capable of self-healing defects. Additionally, we show these films are capable of utilizing functional biomolecules by incorporating an enzyme into the SRT multilayer. Urease was chosen as a model enzyme of interest to test its activity via fluorescence assay. Successful construction of the SRT films demonstrates the use of mechanically stable self-healing coatings, which can incorporate biomolecules for more complex protective functionalities for advanced functional fabrics

Structural Protein-Based Whispering Gallery Mode Resonators

Nature provides a set of solutions for photonic structures that are finely tuned, organically diverse, and optically efficient. Exquisite knowledge of structure–property relationships in proteins aids in the design of materials with desired properties for building devices with novel functionalities, which are difficult to achieve or previously unattainable. Here we report whispering-gallery-mode (WGM) microresonators fabricated entirely from semicrystalline structural proteins (i.e., squid ring teeth, SRT, from Loligo vulgaris and its recombinant) with quality factors as high as 10⁵. We first demonstrate versatility of protein-based devices via facile doping, engaging secondary structures. Then we investigate thermorefractivity and find that it increases with β-sheet crystallinity, which can be altered by methanol exposure and is higher in the selected recombinant SRT protein than its native counterpart. We present a set of photonic devices fabricated from SRT proteins such as add-drop filters and fibers. Protein-based microresonators demonstrated in this work are highly flexible and robust where quality factors and spectral position of resonances are unaffected from mechanical strain. We find that the thermo-optic coefficients of SRT proteins are nearly 100× larger than silica and more than 10× larger than polydimethylsiloxane. Finally, we demonstrate an optical switch utilizing the surprisingly large thermorefractivity of SRT proteins. Achieving 41 dB isolation at an input power of 1.44 μW, all-protein optical switch is 10× more energy efficient than a conventional (silica) thermo-optic switch