Animal silks are protein fibers spun from spiders and silkworms, etc. Silks offer the combined advantages of high strength, high elastic modulus, and large extensibility and are often used as a powerful example of the biological material design paradigm to guide synthetic polymer designs. Although industrial spinning technologies have made great progress, no synthetic polymer fiber has comprehensive mechanical performance that can be comparable with silks. In-depth study of the structure-property-function relationship of silks can not only provide theoretical and fundamental understandings for the application of silk-sourced materials but also can inspire the design and fabrication of high-performance synthetic materials. Dynamic mechanical behavior of silk is studied by continuous dynamic analysis (CDA). Observations indicate that instead of the simple linear-elastic response detected in quasistatic tensile measurements, a different structure−mechanic response occurs before the yield point. By introducing the time variable into the standard three parameter Maxwell model, a structure−mechanic model based on viscoelastic theory was established to understand the contribution of secondary structures to the continuous dynamic mechanical behavior of silk. Humidity-induced actuation is also a unique characteristic of silks that responds to surrounding humidity. The reversible ordered GGY motifs in the amorphous region of silk are proposed to play a crucial role in humidity-induced actuation relied on the results from synchrotron Fourier transform infrared micro spectroscopy as well as small- and wide-angle x-ray scattering. A model based on mean-field theory for understanding the energy storage and dispersion during mechanical loading, the entire humidity-silk response process, including both supercontraction and humidity-induced cyclic actuation, is well quantified. Furthermore, the study of contribution of mesoscale fibrillar architectures to the fracture resistance of Bombyx mori and Antherea yamamai silks confirmed that nanofibrils can improve the ductility and damage tolerance of the silk fibers through non-slip kinematics, restricted fibril shearing, and controlled slippage. Under the guidance of the above research results, a series of silk-based and silk protein-based function materials are developed, including strong silk fiber microactuators, functional silk-based yarns and textiles (e. g., sensing, power generation, display) and silk ionotronics.

Structure-property-function relationship of animal silks and their extended applications

ACS Spring 2022

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