Β‐Sheet Nanocrystals Dictate Water Responsiveness of Bombyx Mori Silk. Issue 7 (3rd March 2020)

• Record Type: Journal Article
• Authors: Park, Yaewon; Jung, Yeojin; Li, Tai‐De; Lao, Jianpei; Tu, Raymond S.; Chen, Xi
• Is Part Of: Macromolecular rapid communications. Volume 41:Issue 7(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-03-03
• Subjects: actuators -- silk -- water‐responsive materials -- β‐sheet nanocrystals; Macromolecules -- Periodicals; Polymers -- Periodicals; Chemistry -- Periodicals; 547.705
• DOI: 10.1002/marc.201900612
• Languages: English
• ISSNs: 1022-1336

Abstract

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 regenerated Bombyx (B.) mori silk 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 of B. mori silk opens up possibilities for simple and scalable modification and production of powerful WR actuators. Abstract : Regenerated Bombyx ( B .) mori silk is processed to increase β‐sheet crystallinity, which dramatically increases the water‐responsive (WR) actuation energy density, surpassing that of all known natural muscles. The finding of the unexpected relationship between the β‐sheet crystallinity and silk's WR energy density suggests a general design rule, opening up new avenues for the fabrication of existing materials toward high‐energy and high‐efficiency WR actuation.