Bidirectional Actuation of Silk Fibroin Films: Role of Water and Alcohol Vapors

Abstract

shape morphism observed in nature inspires the development of stimuli-responsive soft actuators. Vapor-responsive actuators are promising among the different stimuli-responsive materials due to their capability to produce macroscale movements in response to a minuscule amount of specific chemical vapor. Here, we report unusual multiple vapor-responsive bidirectional macroscale actuation behaviors of single-layer regenerated silk fibroin films. The vaporresponsive silk fibroin actuator exhibits antagonistic actuation characteristics in a reversible manner to both water and ethanol vapors. For instance, it produces an upward bending in the presence of water vapor and downward bending in ethanol vapor, which demonstrates the chemical vapor-specific actuation. However, the actuation characteristics remain largely invariant upon changing the polarity of alcohol molecules. The silk fibroin actuators effectively utilize the vapor-induced minuscule expansion and contraction of the film surface to produce large-scale actuation, which is fully reversible. The intrinsic water content of the films and the vapor pressure of the stimulants are exploited to control the actuation performance. Further, we demonstrated the 3D shape morphing ability of the actuator by generating an undulating wavelike motion via preprogrammed water and ethanol vapor exposure conditions. The change in the actuation direction is instantaneous, which ensures the sensitivity and rapid response of the fabricated actuators.

Energy harvesting technology based on moisture-responsive actuators

“…In addition to these common moisture-responsive materials, materials with other organic/inorganic components have been designed to perform moisture-responsive bending deformation. For example, Satapathy's group 92,127 reported on a MRA made from silk proteins (Fig. 3g).…”

Multivapor-Responsive Controlled Actuation of Starch-Based Soft Actuators

“…The inherent flexibility and responsiveness of vapor-driven soft actuators characterized by their undulating wave-like motion make them suitable for precise and controlled fluid manipulation. These actuators rely solely on the expansion and contraction of materials when exposed to stimulus vapors.…”

“…This is due to the constant exchange of vapor between the human body and the surrounding environment, rendering vapor-driven soft actuators exceptionally well-suited for such applications. 9,20 The inherent flexibility and responsiveness of vapor-driven soft actuators characterized by their undulating wave-like motion 16 make them suitable for precise and controlled fluid manipulation. These actuators rely solely on the expansion and contraction of materials when exposed to stimulus vapors.…”

Calla Lily flower inspired morphing of flat films to conical tubes

“…Motions previously achieved using motors and mechanical actuators are replaced by smart actuators that respond to specific stimuli 6–9 . Stimuli‐responsive actuators like light/heat‐responsive liquid crystal polymers, solvent/vapor‐responsive hydrogels and heat‐responsive shape memory alloys were recently developed 4,5,10–25 . Inspired by nature, researchers have developed actuators that can perform complex actions using these responsive systems.…”

“…[6][7][8][9] Stimuli-responsive actuators like light/heatresponsive liquid crystal polymers, solvent/vapor-responsive hydrogels and heat-responsive shape memory alloys were recently developed. 4,5,[10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] Inspired by nature, researchers have developed actuators that can perform complex actions using these responsive systems. Actuators which mimick the blooming of flowers, [26][27][28][29][30] motion of caterpillars, [31][32][33] trapping of flies like Venus flytrap 6 and tight rolling of proboscis of butterfly, 34,35 among others, were developed.…”