Protein Self-Assemblies That Can Generate, Hold, and Discharge Electric Potential in Response to Changes in Relative Humidity

Abstract

Generation of electric potential upon external stimulus has attracted much attention for the development of highly functional sensors and devices. Herein, we report large-displacement, fast actuation in the self-assembled engineered repeat protein Consensus Tetratricopeptide Repeat protein (CTPR18) materials. The ionic nature of the CTPR18 protein coupled to the long-range alignment upon self-assembly results in the measured conductivity of 7.1 × 10 S cm, one of the highest reported for protein materials. The change of through-thickness morphological gradient in the self-assembled materials provides the means to select between faster, highly water-sensitive actuation or vastly increased mechanical strength. Tuning of the mode of motion, e.g., bending, twisting, and folding, is achieved by changing the morphological director. We further show that the highly ionic character of CTPR18 gives rise to piezo-like behavior in these materials, exemplified by low-voltage, ionically driven actuation and mechanically driven generation/discharge of voltage. This work contributes to our understanding of the emergence of stimuli-responsiveness in biopolymer assemblies.

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

“…S7). Given its lamellar structure and excellent swelling rate resulting from water absorption, the pollen paper appeared to exhibit a degree of mechanical responsiveness to humidity somewhat similar to that of many synthetic materials studied previously (14,18,22,25).…”

“…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). Owing to their dynamic responsiveness, these actuators have a wide range of potential applications, including soft robots (12)(13)(14)(15)(16)(17), artificial muscles (18)(19)(20)(21), sensors (22,23), and electric generators (24,25).…”

MXene‐Based Humidity‐Responsive Actuators: Preparation and Properties

“…Actuators are devices that can realize reversible shape change under external stimuli (such as light, [1][2][3] heat, [4][5][6] electricity, [7][8][9] humidity [3,10,11] and magnetism [12,13] ), or convert other forms of energy into mechanical deformation and realize functions such as bending, moving, grasping and stretching. [14][15][16] The traditional motor system can also perform some functions of actuators, but its development is hindered by its huge volume, complex devices and low energy efficiency.…”

Hygroresponsive Torsional Yarns and Actuators Based on Cascade Amplification of the Deformation

“…[ 9,10 ] They are produced by distinctive swelling or shrinkage in hierarchically assembled structures of cellulose microfibrils in response to the humidity variation. [ 11,12 ] Motivated by torsional motions in plants, several hygroresponsive fiber‐based torsional actuators have been investigated, owing to their twisted structures that can store and release energy, coupled with other desirable properties, such as light weight, miniaturization, and shapeability. Despite remarkable progress in this research direction, [ 13 ] it remains a challenge to develop fiber‐based hygroresponsvie torsional actuators that integrates large actuation and rapid response.…”