Light-responsive Actuator Research Articles

Photothermal-driven soft actuator capable of alternative control based on coupled-plasmonic effect

Recent advancements in small-scale soft actuators have showcased their ability to respond to various stimuli, making them ideal for biomedical engineering and robotics. Light-responsive actuators constructed from photothermal materials such as carbon-based materials have received great attention for their remote wireless control ability. However, conventional carbon-based actuators typically exhibit uniform responses to different light wavelengths, limiting the complexity of their control. To address this limitation, this study develops light-driven soft actuators utilizing gold nanorods (Au NRs) to enhance selective photo-responsiveness. Au NRs are incorporated given their superior ability to convert light energy into localized heat through localized surface plasmon resonances, with efficiency varying based on their size and the wavelength of incident light. By adjusting the specifications of the Au NRs and the wavelength of the optical field, tunable actuation efficiency can be achieved. Experimental calibration confirms that the actuator exhibits differential performance across various wavelengths, enabling more precise control over its behavior. Demonstrations of application devices highlight the actuator’s versatility in flexible robotics, showcasing its potential for advanced applications. This innovation represents a considerable step towards achieving more adaptable and functional soft robotic systems, paving the way for future developments in this area.

A light-responsive poly(urethane-urea) actuator with room temperature self-healing performance

Light-responsive actuators with self-healing properties and super mechanical strength at room temperature are critical for practical applications. However, optimizing both of these properties on a single actuator is extremely challenging. Herein, a novel light-responsive poly(urethane-urea) actuator (PIBS-0.75) with room temperature self-healing performance has been successfully prepared. The PIBS-0.75 light-responsive actuator not only exhibits excellent self-healing properties (heals for 8 h at room temperature and regains 91.16 % of its original tensile strength), but also shows high tensile strength (15.52 MPa) and good fracture strain (over 600 %). Moreover, a bionic light-responsive device with room temperature self-healing properties has been successfully fabricated to imitate human gestures of greeting. By incorporating the room temperature self-healing ability into the light-responsive actuator, this work would pave a new way for the development of durable and sustainable light-responsive actuators.

Superhydrophobic, flexible and high thermal stable ANFs/CNTs film for controllable light driven actuators

Superhydrophobic and light-responsive actuators (SLRAs) can be driven to move on water surface remotely and in a non-contact manner, and have shown promising applications in soft robotics, environmental protection, etc. It remains a big challenge to develop high performance SLRAs with excellent thermal stability, fast light responsivity and controllable motion. Here, we propose a layer-by-layer vacuum filtration method to prepare flexible, freestanding and superhydrophobic composite films composed of alternately deposited oleylamine modified acid carbon nanotubes (O-ACNTs) and aramid nanofibers (ANFs). The composite film has excellent thermal stability with the maximum weight loss rate temperature as high as 520 ℃. The closely packed structure and strong interlayer interaction ensure the surface stability and durability of the composite film. The composite film possesses excellent photothermal conversion performance, and can maintain the structure integrity without deformation when its surface temperature reaches 208 °C. When used as a self-propelled actuator, the SLRA film can response to the light quickly and move on the water surface, and the motion speed and direction can be controlled by adjusting the irradiation intensity and position. The outstanding thermal stability guarantees the stability and reliability of the self-propelled motions. The present study opens a new avenue to design high performance SLRAs.

Deformation-controlled and ultrasensitive polyimide/paraffin wax/carbon nanotube composite NIR-responsive photoactuators

Light-responsive actuators have become increasingly popular in various fields such as soft robotics, biomedical devices, and photosensitive electronic devices due to their remote wireless operation and high deformation efficiency. However, controlling actuator deformation efficiency and modes remains a significant challenge. Herein, a new 3D printed polyimide (PI)/paraffin wax (PW)/carbon nanotube (CNT) NIR-responsive photoactuators with controlled deformation mode and ultrasensitive light response has been proposed. The process involves printing a CNT slurry according to a predetermined path, followed by lamination with PW and PI film to create PI/PW/CNT (PPC) NIR responsive photoactuators. Then, the effects of the CNTs pattern (line width and line spacing) on the deformation efficiency were studied and optimized. Upon optimization, the deformation time can be reduced to 3 s and the deformation angle can be raised to 70°. Moreover, the PPC actuator is highly sensitive to temperature and can be deformed within a temperature difference of about 2–3 °C. Finally, various PPC photoactuators including Flower-shape and soft mechanical hand have been prepared to present the different deformation forms. Overall, this work presents a new approach to researching multifunctional NIR-responsive photoactuators with adjustable deformation structures.

Fabricating 3D Moisture- and NIR Light-Responsive Actuators by a One-Step Gradient Stress-Relaxation Process.

Polymeric materials that can actuate under the stimulation of environmental signals have attracted considerable attention in fields including artificial muscles, soft robotics, implantable devices, etc. To date, the improvement of shape-changing flexibility is mainly limited by their unchangeable shapes and structural and compositional distributions. In this work, we report a one-step treatment process to convert 2D poly(ethylene oxide)/sodium alginate/tannic acid thin films into 3D-shaped moisture- and NIR light-responsive actuators. Spatial surface wetting of the film leads to the release of residual stress generated in film formation in a gradient manner, which drives the wetted regions to bidirectionally bend. By controlling the position and bending amplitude of the wetted regions, designated 3D shapes can be obtained. Moreover, Fe3+ ions in the aqueous solution used for surface wetting can coordinate with carboxylate groups in sodium alginate chains to form a gradient cross-linking network. This gradient network can not only stabilize the resulting 3D shape but also render the film with moisture-responsive morphing behaviors. Fe3+ ions can also self-assemble with tannic acid molecules to form photothermal aggregates, making the film responsive to NIR light. We further show that films with versatile 3D shapes and different modes of deformation can be fabricated by a one-step treatment process. This strategy is convenient and extendable to develop 3D-shaped polymer actuators with flexible shape-changing behaviors.

Light-driven Bi-stable actuator with oriented polyimide fiber reinforced structure

The unique feature of bi-stable structure is that it has the inherent ability to rapidly change between two stable configurations under external stimulations, and can maintain the equilibrium state without energy consumption. Herein, we reported a light-responsive bi-stable actuator which composed of functional and support layers. Firstly, the effect of oriented polyimide (PI) fiber-reinforced polydimethylsiloxane (PDMS) composites on thermal behavior was been studied. Then, this unique thermal performance of PI fiber-reinforced PDMS in combination with the laying method ensures the formation of a bi-stable actuator. Finally, a universal but straightforward strategy to generate a light-responsive actuator with fast deformation and bi-stable characteristics was developed based on photo-thermal expansion deformation mechanism. Moreover, the actuator was fabricated by using inexpensive materials and scalable methods. Overall we believe this work may open up a new perspective for the design of light-responsive actuators and enriches the design of fast-deformation flexible bi-stable actuators.

Thermal-/Light-Tunable Hydrogels Showing Reversible Widening and Closing Actuations Based on Predesigned Interpenetrated Networks

Poly(N-isopropylacrylamide) (PNIPAM) is a well-known biocompatible temperature-sensitive polymer. To enhance the biocompatibility of the artificial iris developed in our previous work, in this study, we demonstrate the syntheses of a series of cross-linked and interpenetrated poly(NIPAM-co-AM) hydrogel networks. Elasticities and mechanical properties of the synthesized hydrogels were investigated. Based on the results, the N3A1–N3A1 interpenetrated network (IPN) hydrogel was selected as a functional material for the fabrication of thermally tunable and light-tunable iris-like actuators. Fabrication of both gradient- and double-layer hydrogels was also carried out. Thermally responsive curling of the synthesized hydrogels was studied. Fabrication of thermal-/light-tunable IPN hydrogels showing actuation of widening and closing was achieved. The synthesized iris-like IPN hydrogels were further coated with polydopamine to promote light sensitivity. Both thermally sensitive actuation and light-sensitive actuation of widening and closing were demonstrated for the fabricated iris-like hydrogels. Stimulated variations in the inner diameter and the outer diameter surrounding the iris-like hydrogels were estimated. The results showed that poly(NIPAM-co-AM) IPN hydrogels are available for the design of thermal-/light-responsive actuators.

Bioinspired near-infrared light-induced ultrafast soft actuators with tunable deformation and motion based on conjugated polymers/liquid crystal elastomers

Conjugated polymers (CPs) with remarkable photothermal effect were incorporated into liquid crystal elastomers (LCEs) to develop near-infrared (NIR) light-responsive actuators with tunable deformation and locomotion.

Light-Responsive Soft Actuators: Mechanism, Materials, Fabrication, and Applications

Soft robots are those that can move like living organisms and adapt to the surrounding environment. Compared with traditional rigid robots, the advantages of soft robots, in terms of material flexibility, human–computer interaction, and biological adaptability, have received extensive attention. Flexible actuators based on light response are one of the most promising ways to promote the field of cordless soft robots, and they have attracted the attention of scientists in bionic design, actuation implementation, and application. First, the three working principles and the commonly used light-responsive materials for light-responsive actuators are introduced. Then, the characteristics of light-responsive soft actuators are sequentially presented, emphasizing the structure strategy, actuation performance, and emerging applications. Finally, this review is concluded with a perspective on the existing challenges and future opportunities in this nascent research frontier.

Arbitrarily Reconfigurable and Thermadapt Reversible Two-Way Shape Memory Poly(thiourethane) Accomplished by Multiple Dynamic Covalent Bonds.

The fabrication of a single polymer network that exhibits a good reversible two-way shape memory effect (2W-SME), can be formed into arbitrarily complex three-dimensional (3D) shapes, and is recyclable remains a challenge. Herein, we design and fabricate poly(thiourethane) (PTU) networks with an excellent thermadapt reversible 2W-SME, arbitrary reconfigurability, and good recyclability via the synergistic effects of multiple dynamic covalent bonds (i.e., ester, urethane, and thiourethane bonds). The PTU samples with good mechanical performance simultaneously demonstrate a maximum tensile stress of 29.7 ± 1.1 MPa and a high strain of 474.8 ± 7.5%. In addition, the fraction of reversible strain of the PTU with 20 wt % hard segment reaches 22.4% during the reversible 2W-SME, where the fraction of reversible strain is enhanced by self-nucleated crystallization of the PTU. A sample with arbitrarily complex permanent 3D shapes can be realized via the solid-state plasticity, and that sample also exhibits excellent reversible 2W-SME. A smart light-responsive actuator with a double control switch is fabricated using a reversible two-way shape memory PTU/MXene film. In addition, the PTU networks are de-cross-linked by alcohol solvolysis, enabling the recovery of monomers and the realization of recyclability. Therefore, the present study involving the design and fabrication of a PTU network for potential applications in intelligent actuators and multifunctional shape-shifting devices provides a new strategy for the development of thermadapt reversible two-way shape memory polymers.

A bidirectionally reversible light-responsive actuator based on shape memory polyurethane bilayer

In this work, a simple method is proposed for the preparation of bidirectionally reversible light-responsive shape memory polyurethane (SMPU) bilayer. This SMPU bilayer consists of a 4,4-azodibenzoic acid (Azoa) containing SMPU (SMPU-Azoa) layer and a carbon black (CB) containing SMPU (SMPU-CB) layer. A reversible deformation is realized when the two sides are exposed to ultraviolet (UV) and infrared (IR) lights, respectively. The working mechanism is the trans–cis isomerization of SMPU-Azoa layer and the photo-thermal effect of SMPU-CB layer. The effect of the filler content and the thickness ratio of bilayer is systematically studied. The reversible bending angle of the SMPU bilayer can exceed 30° in 16 s for one cycle when the Azoa and CB contents are 5 wt% and 0.5 wt%, respectively, and the thickness ratio of SMPU-Azoa layer to SMPU-CB layer is 1/1.3. Furthermore, a micro-robot based on such LSMP bilayer is demonstrated.

A facile approach for the preparation of liquid crystalline polyurethane for light-responsive actuator films with self-healing performance

A facile approach was developed to prepare liquid crystalline polyurethane by quaternization between ordinary polyurethane and liquid crystalline monomers to yield a fast light-responsive actuator film with self-healing performance.

Synthesis of Core-Modified Third-Generation Light-Driven Molecular Motors.

The synthesis and characterization of a series of light-driven third-generation molecular motors featuring various structural modifications at the central aromatic core are presented. We explore a number of substitution patterns, such as 1,2-dimethoxybenzene, naphthyl, 1,2-dichlorobenzene, 1,1′:2′,1″-terphenyl, 4,4″-dimethoxy-1,1’:2′,1″-terphenyl, and 1,2-dicarbomethoxybenzene, considered essential for designing future responsive systems. In many cases, the synthetic routes for both synthetic intermediates and motors reported here are modular, allowing for their post-functionalization. The structural modifications introduced in the core of the motors result in improved solubility and a bathochromic shift of the absorption maxima. These features, in combination with a structural design that presents remote functionalization of the stator with respect to the fluorene rotors, make these novel motors particularly promising as light-responsive actuators in covalent and supramolecular materials.

Light-Responsive Actuators Based on Graphene.

As a typical 2D carbon material, graphene, that possesses outstanding physical/chemical properties, has revealed great potential for developing soft actuators. Especially, the unique properties of graphene, including the excellent light absorption property, softness, and thermal conductivity, play very important roles in the development of light-responsive graphene actuators. At present, various light-driven actuators have been successfully developed based on graphene and its derivatives. In this mini review, we reviewed the recent advances in this field. The unique properties of graphene or graphene-related materials that are of benefit to the development of light-driven actuators have been summarized. Typical smart actuators based on different photothermal/photochemical effects, including photothermal expansion, photothermal desorption, photoisomerization, and photo-triggered shape memory effect, have been introduced. Besides, current challenges, and future perspective have been discussed. The rapid progress of light-responsive actuators based on graphene has greatly stimulated the development of graphene-based soft robotics.

Revisiting and Redesigning Light-Activated Cyclic-Mononucleotide Phosphodiesterases

As diffusible second messengers, cyclic nucleoside monophosphates (cNMPs) relay and amplify molecular signals in myriad cellular pathways. The triggering of downstream physiological responses often requires defined cNMP gradients in time and space, generated through the concerted action of nucleotidyl cyclases and phosphodiesterases (PDEs). In an approach denoted optogenetics, sensory photoreceptors serve as genetically encoded, light-responsive actuators to enable the noninvasive, reversible, and spatiotemporally precise control of manifold cellular processes, including cNMP metabolism. Although nature provides efficient photoactivated nucleotidyl cyclases, light-responsive PDEs are scarce. Through modular recombination of a bacteriophytochrome photosensor and the effector of human PDE2A, we previously generated the light-activated, cNMP-specific PDE LAPD. By pursuing parallel design strategies, we here report a suite of derivative PDEs with enhanced amplitude and reversibility of photoactivation. Opposite to LAPD, far-red light completely reverts prior activation by red light in several PDEs. These improved PDEs thus complement photoactivated nucleotidyl cyclases and extend the sensitivity of optogenetics to red and far-red light. More generally, our study informs future efforts directed at designing bacteriophytochrome photoreceptors.

Space-Confined Seeded Growth of Cu Nanorods with Strong Surface Plasmon Resonance for Photothermal Actuation.

Herein, we show that copper nanostructures, if made anisotropic, can exhibit strong surface plasmon resonance comparable to that of gold and silver counterparts in the near-infrared spectrum. Further, we demonstrate that a robust confined seeded growth strategy allows the production of high-quality samples with excellent control over their size, morphology, and plasmon resonance frequency. As an example, copper nanorods (CuNRs) are successfully grown in a limited space of preformed rod-shaped polymer nanocapsules, thereby avoiding the complex nucleation kinetics involved in the conventional synthesis. The method is unique in that it enables the flexible control and fine-tuning of the aspect ratio and the plasmonic resonance. We also show the high efficiency and stability of the as-synthesized CuNRs in photothermal conversion and demonstrate their incorporation into nanocomposite polymer films that can be used as active components for constructing light-responsive actuators and microrobots.

A surface-engineered NIR light-responsive actuator for controllable modulation of collective cell migration.

Mechanical signal transduction is fundamental for maintaining and regulating cellular processes and functions. Here, we proposed a novel near-infrared (NIR) light-responsive optomechanical actuator for the directional regulation of collective cell adhesion and migration. This optomechanical actuator that is made up of a thermal-responsive copolymer hydrogel and gold nanorods (AuNRs), enables non-invasive activation by NIR light stimulation. The activation of the optomechanical actuator leads to hydrogel contraction and an increase in Young's modulus, which could be used for applying contraction force to cells cultured on the surface of the hydrogel actuator. By grafting cell adhesive peptide ligands, the cells could attach onto the surface of the actuator and displayed a NIR light illumination intensity dependent migration rate along a random orientation. To achieve the controllable modulation of cell behaviors, we employed a microcontact printing strategy for patterned presentation of adhesive ligands on this actuator and achieved directional cell alignment and cell migration through optomechanical actuation. These demonstrations suggest that this robust optomechanical actuator is promising for the optical modulation of cellular events and cell functions in various bioapplications.

Naphthalocyanine as a New Photothermal Actuator for Lipid-Based Drug Delivery Systems.

One approach to address the substantial global burden of ocular diseases such as aged related macular degeneration is using light-activated drug delivery to obviate the need for highly invasive and frequent, costly intravitreal injections. To enable such systems, new light responsive materials are required. This communication reports the use of silicon 2,3-naphthalocyanine bis(trihexylsilyloxide) (SiNC), a small molecule photosensitizer, as a new actuator for triggering light responsive lipid-based drug delivery systems. Small-angle X-ray scattering was used to confirm that the addition of SiNC imparted light sensitivity to the lipid systems, resulting in a complete phase transition within 20 s of near-infrared irradiation. The phase transition was also reversible, suggesting the potential for on-demand drug delivery. When compared to the phase transitions induced using alternative light responsive actuators, gold nanorods and graphene, there were some differences in phase behavior. Namely, the phytantriol with SiNC system transitioned directly to the inverse micellar phase, skipping the intermediate inverse hexagonal structure. The photodynamic properties and efficiency in controlling the release of drug suggest that SiNC-actuated lipid systems have the potential to reduce the burden of repeated intravitreal injections.

A remote controllable fiber-type near-infrared light-responsive actuator.

A novel near-infrared (NIR) light-responsive sodium polyacrylate (PAAS)/graphene oxide (GO) fiber with a torsional pre-deformation structure is reported to realize remote control actuation. The torsional pre-deformed PAAS/GO fiber exhibited various actuation phenomena, under the control of a low powered near-infrared light (50 mW cm-2), such as rotating in a low-temperature range (<25 °C), rolling a distance of 10 times of its diameter within 10 s, and even driving the shape change of a fabric (the weight is as high as 20 times of the fiber itself).

NIR-Vis-UV Light-Responsive Actuator Films of Polymer-Dispersed Liquid Crystal/Graphene Oxide Nanocomposites.

To take full advantage of sunlight for photomechanical materials, NIR-vis-UV light-responsive actuator films of polymer-dispersed liquid crystal (PDLC)/graphene oxide (GO) nanocomposites were fabricated. The strategy is based on phase transition of LCs from nematic to isotropic phase induced by combination of photochemical and photothermal processes in the PDLC/GO nanocomposites. Upon mechanical stretching of the film, both topological shape change and mesogenic alignment occurred in the separated LC domains, enabling the film to respond to NIR-vis-UV light. The homodispersed GO flakes act as photoabsorbent and nanoscale heat source to transfer NIR or VIS light into thermal energy, heating the film and photothermally inducing phase transition of LC microdomains. By utilizing photochemical phase transition of LCs upon UV-light irradiation, one azobenzene dye was incorporated into the LC domains, endowing the nanocomposite films with UV-responsive property. Moreover, the light-responsive behaviors can be well-controlled by adjusting the elongation ratio upon mechanical treatment. The NIR-vis-UV light-responsive PDLC/GO nanocomposite films exhibit excellent properties of easy fabrication, low-cost, and good film-forming and mechanical features, promising their numerous applications in the field of soft actuators and optomechanical systems driven directly by sunlight.