Multiresponsive Actuators Research Articles

Ultrafast Fabrication of Gradient Nanoporous All‐Polysaccharide Films as Strong, Superfast, and Multiresponsive Actuators

AbstractThe design of smart hydrogel actuators fully constructed from natural polymers for assessing the biomedical applications is important but challenging. Herein, an extremely simple, green, and ultrafast strategy is presented for preparing robust gradient all‐polysaccharide polyelectrolyte complex hydrogel actuators. Driven by diffusing of low molecular weight chitosan into high molecular weight sodium alginate solution, a nanoporous, ultrastrong, and gradient chitosan/sodium alginate complex hydrogel film with adjustable thickness can be directly generated on the interface of two solutions within minutes. The as‐prepared film can provide superfast temperature, ionic strength, and pH‐triggered programmable deformations, and perform a distinct sequential double folding behavior due to the competitive effect between complexed and noncomplexed segments of polyelectrolyte. Besides, patterning Ca2+ to locally crosslink sodium alginate in the film enables various more complex shape transformations. This green and simple diffusion‐driven strategy provides significant guidance for fabricating bio‐friendly actuators with applications in drug delivery, tissue engineering, soft robotics, and active implants.

Multiresponsive actuators based on modified electrospun films.

Robot technology has made great progress over the past few decades, and has found wide use in military, industrial and service fields. In recent years, there has been a dramatic increase in the demand for soft robots. However, as a key part, the development of soft actuators capable of low-energy actuation, multi-stimulation response, and large shape deformation is still challenging. In this work, we fabricated multiresponsive actuators based on modified electrospun films. The actuators provided the largest curvatures of 0.83 cm−1, 0.6 cm−1, and 1.05 cm−1, stimulated by humidity, light, and electricity, respectively. Furthermore, we designed a biomimetic application—a crawling robot—which demonstrates excellent potential applications of the actuator in soft robotics, artificial muscles, and the biomimetics field.

Tetracarboxylated Azobenzene/Polymer Supramolecular Assemblies as High-Performance Multiresponsive Actuators.

Multistimuli-responsive polymers are materials of emerging interest but synthetically challenging. In this work, supramolecular assembly was employed as a facile and effective approach for constructing 3,3',5,5'-azobenzenetetracarboxylic acid (H4abtc)/poly(diallyldimethylammonium chloride) (PDAC) supramolecules. Structural transformations of H4abtc can be induced by light, mechanical force, and heat and influenced by free volume. Thus, the fabricated free-standing H4abtc/PDAC film underwent bending/unbending movements upon treatment with light, humidity, or temperature, as asymmetric structural transformations on either side of the film generated asymmetric contraction/stretching forces. Fast rates of shape recovery were achieved for the film on exposure to gently flowing humid nitrogen. The bending/unbending motions are controllable, reversible, and repeatable. Hence, this light-, humido-, and thermo-responsive film has great potential in device applications for advanced functions.

Multi-responsive actuators based on a graphene oxide composite: intelligent robot and bioinspired applications.

Carbon-based electrothermal or photothermal actuators have attracted intense attention recently. They can directly convert electrical or light energy into thermal energy and exhibit obvious deformations. However, if the actuation mechanism is only limited to thermal expansion, the deformation amplitude is difficult to increase further. Moreover, complex shape-deformation is still challenging. Although a few materials were reported to realize twisting or untwisting actuation by cutting the samples into strips along different orientations, each single strip could perform only one shape-deformation mode. In this work, we propose multi-responsive actuators based on a graphene oxide (GO) and biaxially oriented polypropylene (BOPP) composite, which are designed with different shapes (strip-shape and helical-shape). The strip-shape GO/BOPP actuator shows great bending actuations when driven by humidity (curvature of up to 3.1 cm-1). Due to a developed dual-mode actuation mechanism, the actuator shows a bending curvature of 2.8 cm-1 when driven by near infrared (NIR) light. The great actuation outperforms most other carbon-based actuators. Then, an intelligent robot based on the GO/BOPP composite is fabricated, which can switch between the protection mode and weightlifting mode with different external stimuli. Inspired from plant tendrils, a bioinspired helical GO/BOPP actuator is further realized to show both twisting and untwisting actuations in a single actuator, fully mimicking the deformation of plant tendrils. Finally, a robot arm consisting of strip-shape and helical GO/BOPP actuators can grasp an object that is 2.9 times heavier than itself, demonstrating promising bioinspired applications.

Actuators: Multiresponsive Bidirectional Bending Actuators Fabricated by a Pencil‐on‐Paper Method (Adv. Funct. Mater. 40/2016)

A multi-responsive actuator based on paper and polymer composite is fabricated by a Pencil-on-Paper method, which is described by L. Chen, W. Zhang, C. Liu, and co-workers on page 7244. A colorful biomimetic flower and a smart curtain are also fabricated to demonstrate the applications. This work has great potential in the fields of lab-on-paper devices, artificial muscles, robotics, and biomimics.