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Creators/Authors contains: "Jung, Yeojin"

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  1. Abstract

    Biological water-responsive materials that deform with changes in relative humidity have recently demonstrated record-high actuation energy densities, showing promise as high-performance actuators for various engineering applications. However, there is a lack of theories capable of explaining or predicting the stress generated during water-responsiveness. Here, we show that the nanoscale confinement of water dominates the macroscopic dehydration-induced stress of the regenerated silk fibroin. We modified silk fibroin’s secondary structure, which leads to various distributions of bulk-like mobile and tightly bound water populations. Interestingly, despite these structure variations, all silk samples start to exert force when the bound-to-mobile (B/M) ratio of confined water reaches the same level. This critical B/M water ratio suggests a common threshold above which the chemical potential of water instigates the actuation. Our findings serve as guidelines for predicting and engineering silk’s WR behavior and suggest the potential of describing the WR behavior of biopolymers through confined water.

     
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  2. Bombyx mori silk with a nanoscale porous architecture significantly deforms in response to changes in relative humidity. Despite the increasing amount of water adsorption and water-responsive strain with increasing porosity of the silk, there is a range of porosities that result in silk's optimal water-responsive energy density at 3.1 MJ m −3 . Our findings show the possibility of controlling water-responsive materials’ swelling pressure by controlling their nanoporosities. 
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  3. Abstract

    Water‐responsive (WR) materials that strongly swell and shrink in response to changes in relative humidity (RH) have shown a great potential to serve as high‐energy actuators for soft robotics and new energy‐harvesting systems. However, the design criteria governing the scalable and high‐efficiency WR actuation remain unclear, and thus inhibit further development of WR materials for practical applications. Nature has provided excellent examples of WR materials that contain stiff nanocrystalline structures that can be crucial to understand the fundamentals of WR behavior. This work reports that regeneratedBombyx (B.) morisilk can be processed to increase β‐sheet crystallinity, which dramatically increases the WR energy density to 1.6 MJ m−3, surpassing that of all known natural muscles, including mammalian muscles and insect muscles. Interestingly, the maximum water sorption decreases from 80.4% to 19.2% as the silk's β‐sheet crystallinity increases from 19.7% to 57.6%, but the silk's WR energy density shows an eightfold increase with higher fractions of β‐sheets. The findings of this study suggest that high crystallinity of silk reduces energy dissipation and translates the chemical potential of water‐induced pressure to external loads more efficiently during the hydration/dehydration processes. Moreover, the availability ofB. morisilk opens up possibilities for simple and scalable modification and production of powerful WR actuators.

     
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