Nanofibrous Actuator with an Alignment Gradient for Millisecond-Responsive, Multidirectional, Multimodal, and Multidimensional Large Deformation

Abstract

Although progress has been made in the construction of stimulus-responsive actuators, the performance of these smart materials is still unsatisfactory, owing to their slow response, small deformation amplitude, uncontrollable bending direction, and unidirectional (2D to 3D) transformation. Herein, we employ a structural bionic strategy to design and fabricate a novel water/ moisture responsive nanofibrous actuator with an alignment degree gradient. Owing to its different contraction gradient amplitudes along the thickness direction and the unique physical property of the nanofibrous material, the prepared actuator exhibits excellent shape deformation performance, including superfast response (less than 150 ms), controllable deformation directions, multiple actuation models, multiple dimensional deformation (0D−3D, 1D−3D, 2D−3D, and 3D−3D), large bending curvature (25.3 cm −1 ), and a repeatability rate of at least 1000. The actuation performance of the nanofibrous actuator is superior to the currently reported actuators. The nanofibers are integrated into layer-by-layer and side-by-side structures to achieve competitive and independent actuation, respectively. The outstanding shape-changing properties of the nanofibrous actuator result in the construction of practical intelligent devices for applications such as amphibious movement, intelligent protection, and cargo transportation. The nanofibrous actuator designed herein exhibits tremendous potential in soft robotics, sensors, and biomedicine.

Robust and Highly Sensitive Cellulose Nanofiber-Based Humidity Actuators

“…34,35 Song et al reported a single-layered polyvinyl alcohol nanofibrous actuator via the electrospinning technique, which can perform ultrasensitive and complex shape deformations responding to water/moisture. 36 Despite satisfying progress aiming to the actuation response, these strategies generally also involve a time-consuming preparation process and a sophisticated structural design and sometimes impair the mechanical robustness. Therefore, it is still a great challenge to possess superior actuation features including fast response, large-shape deformation, and robust stability without sacrificing their intrinsic flexibility and mechanical robustness in a facile yet friendly way for fabricating humidity actuators.…”

“…For recovery sensitivity, an attractive strategy is to create a hydrophilic–hydrophobic composite system in the homogeneous matrix, wherein the hydrophobic component could help water molecules escape to the external environment, facilitating the water desorption. , Tang et al prepared a humidity actuator using hydrophilic calcium carbonate oligomers and hydrophobic poly (vinylidene fluoride), exhibiting a highly sensitive and reversible actuation . Another interesting strategy is to tune a desirable porous structure, providing a sufficient contact area for exposing more water-absorbed sites, and introducing more nanochannels to accelerate water transport and diffusion, thus contributing to the rapid adsorption and desorption of water molecules. , Song et al reported a single-layered polyvinyl alcohol nanofibrous actuator via the electrospinning technique, which can perform ultrasensitive and complex shape deformations responding to water/moisture . Despite satisfying progress aiming to the actuation response, these strategies generally also involve a time-consuming preparation process and a sophisticated structural design and sometimes impair the mechanical robustness.…”

Light-Responsive Nanofibrous Motor with Simultaneously Precise Locomotion and Reversible Deformation

“…Generally, polymer chains in the nanofibers are strongly pulled by the electrostatic repulsive force during the electrospinning process. , When the motor is incubated into water, water molecules diffuse into the nanofibers and further disrupt the hydrogen bonding between the PVA chains, and the polymer chains relax and contract, leading to a macro contraction for the motor. , As the motor possesses alignment gradient along the thickness direction, an unmatched contraction is formed, which further leads to a 2D to 3D shape deformation for the motor. Under NIR irradiation, water molecules with large surface tension will pull that with small surface tension along with the motor, and the motor will gradually transform from a tubular structure into flat morphology.…”

“…(3) Nanofibrous materials can also generate superior shape changing performance with the design of a tailored microstructure. Very recently, we found that diverse and reversible deformation of the electrospun nanofibrous material can be achieved by construction of nanofiber alignment gradient in the thickness direction . On the basis of these considerations, we intend to prepare the gradient-structured PVA nanofibers and further modify them with NIR-sensitive particles for achieving simultaneous movement and deformation.…”

“…Very recently, we found that diverse and reversible deformation of the electrospun nanofibrous material can be achieved by construction of nanofiber alignment gradient in the thickness direction. 23 On the basis of these considerations, we intend to prepare the gradient-structured PVA nanofibers and further modify them with NIR-sensitive particles for achieving simultaneous movement and deformation. To the best of our knowledge, the design and fabrication of NIR-responsive nanofibrous motors have not yet been reported.…”