Spider dragline silk as torsional actuator driven by humidity

Abstract

Self-powered actuation driven by ambient humidity is of practical interest for applications such as hygroscopic artificial muscles. We demonstrate that spider dragline silk exhibits a humidity-induced torsional deformation of more than 300°/mm. When the relative humidity reaches a threshold of about 70%, the dragline silk starts to generate a large twist deformation independent of spider species. The torsional actuation can be precisely controlled by regulating the relative humidity. The behavior of humidity-induced twist is related to the supercontraction behavior of spider dragline silk. Specifically, molecular simulations of MaSp1 and MaSp2 proteins in dragline silk reveal that the unique torsional property originates from the presence of proline in MaSp2. The large proline rings also contribute to steric exclusion and disruption of hydrogen bonding in the molecule. This property of dragline silk and its structural origin can inspire novel design of torsional actuators or artificial muscles and enable the development of designer biomaterials.

Plasticised Regenerated Silk/Gold Nanorods Hybrids as Sealant and Bio-Piezoelectric Materials

“…By increasing the RS fraction, this effect disappears and a less hydrophilic surface was obtained (Figure 3c). This shrinking effect is very similar to a well-known property of spider silk called super-contraction, in which the silk fibres can suddenly shrink in response to changes in moisture [27]. Spider silk is a protein fibre like silkworm silk.…”

Actuation and locomotion driven by moisture in paper made with natural pollen

“…Examples include the opening of pine cones (4), the dispersion of wheat awn seeds (5), and the unfolding of ice plant seed capsules (6). At the molecular level, biological protein materials such as silk (7) and collagen (8) control their mechanical forces and motions by changing their molecular conformations in response to moisture. Inspiration drawn from such naturally occurring biological systems has led to the development of a wide range of artificial soft actuators that can reversibly alter morphological or mechanical characteristics in response to external stimuli (9)(10)(11).…”

Ultrastrong and Highly Sensitive Fiber Microactuators Constructed by Force‐Reeled Silks

“…It exhibits unique humidity‐induced actuation behavior with a torsional deformation more than 300° mm −1 . This value is thousands of times higher than that of other conventional fiber microactuators, such as conducting polymer actuators (0.01° mm −1 ) and shape‐memory alloy fibers microactuators (0.15° mm −1 ) . In fact, the humidity‐induced actuation of the spider dragline silk is even higher than that of the state of the art of the carbon nanotubes (CNTs) microactuators (250° mm −1 ), which is powered by the electricity.…”

“…For example, spider dragline silk is an extraordinary fiber that surpasses the majority of conventional materials in mechanical characteristics such as the mechanical toughness. Moreover, spider dragline silk has proven to be an outstanding torsional actuator . It exhibits unique humidity‐induced actuation behavior with a torsional deformation more than 300° mm −1 .…”