Bioinspired Smart Moisture Actuators Based on Nanoscale Cellulose Materials and Porous, Hydrophilic EVOH Nanofibrous Membranes

Abstract

Biomimetic actuators with rapid response speed, high sensitivity, and selectivity to external stimulus have found potential applications in smart switches, artificial muscles, and soft robots. The nanoscale structures of actuators enhance the exposed area to stimulus as well as enable versatile control of the actuation behaviors. Freestanding, flexible, and porous water-driven actuators with poly­(vinyl alcohol-co-ethylene) (EVOH) nanofibers as the substrate and super hydrophilic nanoscale cellulose materials (cellulose nanofibers, cellulose nanocrystals, bacterial cellulose) as the active substance via uniform mixing or surface depositing were fabricated. The effects of the EVOH nanofiber substrate, the structures and concentrations of nanoscale cellulose materials, as well as the different environmental stimuli like humidity and temperature on the performance of actuators were studied. The water-driven actuation mechanism was proposed from the macroscopic and molecular aspects and the analysis of Gibbs free energy and mechanical energy. The actuator could bend to an angle of 180° and recovered less than 1 s for more than 100 circles without compromising properties when the environmental moisture changed. Furthermore, the multidimensional deformation behaviors of the water-stimulated actuators could also be well tuned by varying the orientations of the nanoscale materials. Additionally, the applications of the prepared actuator were demonstrated.

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

“…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). 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).…”

“…Given the common limitations associated with these materials in terms of their relatively high cost, strict reaction control, and issues with environmental sustainability, the quest for more cost-effective materials from natural and renewable sources has accelerated (31)(32)(33)(34). Although natural materials such as agarose (24,32,35) and cellulose (11,(36)(37)(38) are used in a number of applications, they must be extracted and refined from raw resources at a considerable energy cost. Furthermore, actuators constructed from some natural polymers typically exhibit a weak actuation response, and their dynamic response is typically not conducive to fabrication of components that demand cyclic variations in mechanical characteristics (39).…”

Impact of Solar Radiation on Chemical Structure and Micromechanical Properties of Cellulose-Based Humidity-Sensing Material Cottonid

“…This behavior can be observed for various plant systems, where the microstructure of the cell walls is used for directed swelling and shrinking processes [3,20]. These biological moving concepts have been an inspiration for the development of a variety of bio-inspired actuators for different applications in recent years to introduce the efficient relationship between structure and function by development of new functional materials [21][22][23]. The available actuation concepts, like one-dimensional bending, which is realized over bilayered systems, with one active and one passive layer with regard to the present stimulus, two-dimensional stretching, buckling or three-dimensional volume expansion, can be adjusted by the microstructure of the polymer-based material systems and have their specific advantages and disadvantages with respect to the indented application.…”

Flexible Actuators for Soft Robotics

“…The mechanism of humidity actuation is attributed to the in‐and‐out migration of water molecules. In pioneering works, many efforts have been made to fabricate humidity‐responsive actuators based on various materials, including cellulose nanofiber, PPy, graphene, polydopamine, and so on. Recently, Arazoe et al .…”