Light-driven Actuators Research Articles

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.

Near-Infrared Light-Driven Shape-Programmable Hydrogel Actuators Loaded with Metal-Organic Frameworks.

Shape-programmable hydrogel-based soft actuators that can adaptively respond to external stimuli are of paramount significance for the development of bioinspired aquatic smart soft robots. Herein, we report the design and synthesis of near-infrared (NIR) light-driven hydrogel actuators through in situ photopolymerization of poly(N-isopropylacrylamide) (PNIPAM) hydrogels loaded with metal-organic frameworks (MOFs) onto the surface of the poly(dimethylsiloxane) (PDMS) thin film. The MOFs can not only function as an excellent photothermal nanotransducer but also accelerate the adsorption/desorption of water due to their porous nanostructure, which speeds up the response rate of the actuators. Shape-programmable hydrogel actuators are fabricated by tailoring the patterning of PDMS thin film, and thus different shape-morphing modes such as directional bending and chiral twisting are observed under the NIR light irradiations. As the proof-of-concept demonstrations, an artificial hand, biomimetic mimosa, and flower are conceptualized with light-driven MOF-containing hydrogel actuators. Interestingly, we are able to achieve an octopus-inspired light-driven soft swimmer upon cyclic NIR illumination due to the fast photoresponsiveness of as-prepared hydrogel actuators. This work can offer insights for fabricating programmable and reconfigurable smart aquatic soft actuators, thus shining a light into their potential applications in emerging fields including soft robots, biomedical devices, and beyond.

Real-time irradiation system using patterned light to actuate light-driven on-chip gel actuators

A light-driven gel actuator is a potential candidate for a single-cell manipulation tool because it allows cells to be manipulated while ensuring less damage. Moreover, a large number of actuators can be integrated into a microfluidic chip because no wiring is required. Previously, we proposed a method for cell manipulation using light-driven gel actuators. However, the system used in the previous work did not allow the targeted cells to be manipulated in real time because the system used in the previous work could only irradiate preprogrammed patterned light. Moreover, when a large number of gel actuators are integrated into a chip, the Gaussian distribution of the laser light source results in the response characteristics of the gel actuators varying with the location of the actuator. In this work, we constructed a system that homogenized the intensity of the patterned light used for irradiation, allowing multiple gel actuators to be driven in parallel in real time. The intensity-homogenized patterned light improved the variations in the response characteristics of the gel actuators, and as a result, we succeeded in actuating gel actuators with various light patterns in real time.

A NIR-Light-Driven Twisted and Coiled Polymer Actuator with a PEDOT-Tos/Nylon-6 Composite for Durable and Remotely Controllable Artificial Muscle.

In this paper, we proposed a novel light-driven polymer actuator that could produce remotely controllable tensile stroke in response to near infrared (NIR) light. The light-driven polymer actuator was composed of a twisted and coiled nylon-6 fiber (TCN) and a thin poly(3,4-ethylenedioxythiophene) doped with p-toluenesulfonate (PEDOT-Tos) layer. By adopting dip-coating methodology with thermal polymerization process, we constructed a thin and uniform PEDOT-Tos layer on the surface of the three-dimensional TCN structure. Thanks to the PEDOT-Tos layer with excellent NIR light absorption characteristic, the NIR light illumination via a small LEDs array allowed the multiple PEDOT-Tos coated TCN actuators to be photo-thermally heated to a fairly consistent temperature and to simultaneously produce a contractile strain that could be modulated as high as 8.7% with light power. The actuation performance was reversible without any significant hysteresis and highly durable during 3000 cyclic operations via repetitive control of the LEDs. Together with its simple structure and facile fabrication, the light-driven actuator can lead to technical advances in artificial muscles due to its attractive benefits from remote controllability without complex coupled instruments and electromagnetic interference.

Superhydrophobic light-driven actuator based on self-densified wood film with a sandwich-like structure

Response actuators based on different stimuli such as light, humidity and temperature have attracted extensive attention due to their advantages in various environments. In this work, a facile top-down strategy is proposed to prepare a light stimuli-responsive self-densified wood film. We constructed a sandwich-like structure by in-situ co-precipitation of Fe3O4, spraying CNT, self-densification and chemical vapor deposition methyltrimethoxysilane (MTMS) on TEMPO-oxidized delignified wood. The CNT/Fe3O4/MTMS wood film exhibits excellent strength (56 Mpa along the fiber direction), superhydrophobicity (water contact angle of 151°) and photothermal conversion performance. The Fe3O4 in the film plays a good role of photothermal conversion, which makes the photothermal conversion effect of the film double that of the wood film sprayed only with CNT. Under near-infrared (NIR) light irradiation and focused sunlight, the film exhibits a light-driven response of linear motion on the water surface. Based on the excellent electrical conductivity and light stimulus responsiveness of the film under NIR irradiation, an electrical switch is successfully designed and can be remotely controlled. Moreover, the film is easy to recycle due to magnetism, it is also very stable under moisture environment due to the protection of the superhydrophobic coating and the dense structure created by self-densification.

Light-Driven Linear Inchworm Motor Based on Liquid Crystal Elastomer Actuators Fabricated with Rubbing Overwriting.

Linear displacement is used for positioning and scanning, e.g., in robotics at different scales or in scientific instrumentation. Most linear motors are either powered by rotary drives or are driven directly by pressure, electromagnetic forces or a shape change in a medium, such as piezoelectrics or shape-memory materials. Here, we present a centimeter-scale light-powered linear inchworm motor, driven by two liquid crystal elastomer (LCE) accordion-like actuators. The rubbing overwriting technique was used to fabricate the LCE actuators, made of elastomer film with patterned alignment. In the linear motor, a scanned green laser beam induces a sequence of travelling deformations in a pair of actuators that move a gripper, which couples to a shaft via friction moving it with an average speed in the order of millimeters per second. The prototype linear motor demonstrates how LCE light-driven actuators with a limited stroke can be used to drive more complex mechanisms, where large displacements can be achieved, defined only by the technical constrains (the shaft length in our case), and not by the limited strain of the material. Inchworm motors driven by LCE actuators may be scaled down to sub-millimeter size and can be used in applications where remote control and power supply with light, either delivered in free space beams or via fibers, is an advantage.

Light-driven core-shell fiber actuator based on carbon nanotubes/liquid crystal elastomer for artificial muscle and phototropic locomotion

Soft actuators controlled by untethered methods have aroused growing attention on account of their flexibility and controllability. Soft actuators shaped in a one-dimensional structure are highly desired in diverse practical applications. In this paper, we fabricate a new core-shell CNTs@LCE fiber soft actuator made of a liquid crystal elastomer (LCE) fiber coating with carbon nanotubes (CNTs) shell. Thanks to the outstanding photothermal conversion capacity of CNTs and remarkable thermal-contraction characteristic of LCE, the obtained core-shell CNTs@LCE fiber actuator can be controlled by near-infrared light with excellent phototropic bending to arbitrary directions, lifting loads more than 4600 times of its own weight and acting as artificial muscle to control the feature of biomimetic elbow and gripper with loads. More intriguingly, the core-shell CNTs@LCE fiber can fulfill unprecedented photo-driven phototropic locomotion including tracking the moving light source, climbing a slanted surface, and optically steering as well. The involved unique photo-driven phototropic movement mechanism has been revealed experimentally and theoretically, which is highly expected to guide the fabrication of other soft smart fiber actuators for advanced applications.

Programmable light-driven swimming actuators via wavelength signal switching.

Light-driven swimming actuators with different motion modes could lead to many previously unachievable applications. However, controllable navigation often requires focusing light precisely on certain positions of the actuator, which is unfavorable for accurate dynamical operation or in microscale applications. Here, we present a type of programmable swimming actuators that can execute wavelength-dependent multidirectional motions via the Marangoni effect. Several multi–degree of freedom swimming motions have been realized: Forward-and-backward and zigzag actuators can execute one-dimensional (1D) and 2D linear motion, respectively; bidirectional gear rotation as angular motion can be regulated to obtain tunable speeds; and the turning actuator as a “freighter” is able to turn left, right, and go straight for precise maze navigation. A mechanical measurement system is established to quantitatively measure the driving force of the motion directly. The accessible wavelength-selective strategy presented here can inspire further explorations of simple and practical light-driven materials and systems.

Light-Driven Self-Oscillating Actuators with Phototactic Locomotion Based on Black Phosphorus Heterostructure.

Developing self-oscillating soft actuators that enable autonomous, continuous, and directional locomotion is significant in biomimetic soft robotics fields, but remains great challenging. Here, an untethered soft photoactuators based on covalently-bridged black phosphorus-carbon nanotubes heterostructure with self-oscillation and phototactic locomotion under constant light irradiation is designed. Owing to the good photothermal effect of black phosphorus heterostructure and thermal deformation of the actuator components, the new actuator assembled by heterostructured black phosphorus, polymer and paper produces light-driven reversible deformation with fast and large response. By using this actuator as mechanical power and designing a robot configuration with self-feedback loop to generate self-oscillation, an inchworm-like actuator that can crawl autonomously towards the light source is constructed. Moreover, due to the anisotropy and tailorability of the actuator, an artificial crab robot that can simulate the sideways locomotion of crabs and simultaneously change color under light irradiation is also realized.

Giant Bulk Photostriction of Lead Halide Perovskite Single Crystals.

It is well known that the lattice structure for a crystal can be manipulated through mechanical strain, temperature, an electric field, a magnetic field, and light. In the past, the photostriction commonly occurs at the surface and the bulk photostriction is very small in most semiconductors. Here, the 532 nm laser can excite the excess electron-hole pairs in the surface layer and consequently these carriers diffuse in the millimeter-thick MAPbBr3-xIx crystal and introduce a giant bulk photostriction of 0.17, 0.28, and 0.35% for the 0.5 mm-thick MAPbBr3-xIx single crystals at x = 0, 1, and 2, respectively. Furthermore, the displacement of each crystal linearly increases from hundreds of picometers to several micrometers when the light intensity increases from about 0.2 to 536 mW/cm2. Since both the maximum strain and the displacement accuracy are as good as those of PZT ceramics used in piezoelectric actuators, these crystals can be used in light-driven actuators for precise positioning.

Optoregulated force application to cellular receptors using molecular motors

Progress in our understanding of mechanotransduction events requires noninvasive methods for the manipulation of forces at molecular scale in physiological environments. Inspired by cellular mechanisms for force application (i.e. motor proteins pulling on cytoskeletal fibers), we present a unique molecular machine that can apply forces at cell-matrix and cell-cell junctions using light as an energy source. The key actuator is a light-driven rotatory molecular motor linked to polymer chains, which is intercalated between a membrane receptor and an engineered biointerface. The light-driven actuation of the molecular motor is converted in mechanical twisting of the entangled polymer chains, which will in turn effectively “pull” on engaged cell membrane receptors (e.g., integrins, T cell receptors) within the illuminated area. Applied forces have physiologically-relevant magnitude and occur at time scales within the relevant ranges for mechanotransduction at cell-friendly exposure conditions, as demonstrated in force-dependent focal adhesion maturation and T cell activation experiments. Our results reveal the potential of nanomotors for the manipulation of living cells at the molecular scale and demonstrate a functionality which at the moment cannot be achieved by other technologies for force application.

Mechanism research of the laser propulsion of bulk graphene sponge material through high vacuum experiment

Qualitative and quantitative studies have shown that the laser propulsion of bulk graphene sponge material (LPGS) is efficient, green and stable, which has great value in long-term flight, light-driven actuator and optical-mechanical microsystem. However, its mechanism is still in dispute due to the lack of adequate experimental evidence, hindering its applications. In this work, LPGS is comparatively studied under the high vacuum (0.002 Pa) and the rough vacuum (6 Pa). It is observed that LPGS is significant in rough vacuum but disappears in high vacuum, which experimentally refutes the propulsion mechanism based on electron ejection, and confirms that the more reasonable explanation is the laser-induced Knudsen force. This work clears the discussion about the LPGS mechanism and provides an important theoretical basis for the practical use of LPGS.

Light-Driven Crystal-Polymer Hybrid Actuators.

Recently, soft robots, which are made of soft and light organic materials, have attracted much attention because of improved safety for daily interactions with humans. Mechanically responsive materials that can move macroscopically by external stimuli, such as light and heat, have been studied extensively over the past two decades, and they are expected to be applicable to soft robots. Among them, mechanically responsive crystals are attractive in terms of a larger Young’s modulus and faster response speed compared with polymers and gels. However, it is impractical to use one piece of a single crystal as a crystal machine; it is difficult to control the size of crystals and obtain large crystals. Hybridization of crystals with polymers is one way to create actuators with more realistic movements. Herein, we report a hybrid crystal assembly in which plate-like salicylideneaniline crystals are aligned in polymer films by a “rubbing” technique, a new approach which is inexpensive, easy, and applicable to a wide range of crystals and polymers. The hybrid films bent reversibly upon alternate irradiation with ultraviolet and visible light. The hybrid films bent as fast as single crystals, even when larger than single-crystal size, showing great mechanical performance originating from the advantages of both molecular crystals (fast response time) and polymers (large size). This work enriches the development of light-driven hybrid actuators composed of molecular crystals and polymers.

Robust Near-Infrared-Responsive Composite Hydrogel Actuator Using Fe3+/Tannic Acid as the Photothermal Transducer.

Light-driven hydrogel actuators show potential applications because their spatiotemporal precision and contact-free manner, especially for near-infrared light (NIR), can be focused on a specific area, which possesses tunable intensity and strong penetrability. Herein, we propose a novel NIR-responsive hydrogel actuator incorporating Fe3+/tannic acid (Fe3+/TA) as a photothermal transducer into the poly(N-isopropylacrylamide) (PNIPAAm) hydrogel via photo-cross-linking and subsequent immersion in FeCl3 solution. TA contains abundant pyrogallol and catechol groups, which can be linked to PNIPAAm through hydrogen bonds during in situ polymerization; moreover, as a mediator, TA can form metal-phenolic networks with Fe3+ via the coordination between catechol and metal ions, endowing the PNIPAAm gel with enhanced mechanical properties as well as NIR-responsive photothermal effect. We demonstrated that introduction of Fe3+/TA maintained the volume phase transition temperature of the hydrogel around 32 °C and guaranteed its deformation behaviors upon NIR irradiation. Furthermore, a higher concentration level of BIS and Fe3+ were verified to facilitate a stronger photothermal capacity of the hydrogels. Therefore, under NIR irradiation, Fe3+/TA within the hydrogel converted NIR light into heat, and the local high temperature in the irradiated region would cause the petals of the "snowflake"-shaped hydrogel to bend upward perpendicular to the horizontal plane within 1 min, possessing excellent repeatability. This study puts forward a new idea of preparing NIR-responsive hydrogel actuators based on Fe3+/TA, which show promising application in the fields of biomimetic devices, flowing control, and soft robotics.

Visible-light-driven isotropic hydrogels as anisotropic underwater actuators

Photo-driven hydrogel actuators have attracted tremendous attention due to their underwater photo-mechanical applications, but these critical limitations include reliance on harmful UV light, slow driving speed and limited transformation morphologies need to be further resolved. Here, the transparent polyurethane (PU) hydrogels containing dual networks of dynamic covalent crosslinked hexaarylbiimidazole (HABI) and permanent-crosslinked pentaerythritol units are fabricated and exhibit diversified anisotropic transformations in response to visible light. The underwater three-dimensional (3D) actuations including curling, twisting and folding can be spatiotemporally programmed and achieved within tens of seconds. The biomimetic flower and hydrogel wheel enable rapid photo-driven locomotion. The hydrogel actuators possess great fatigue resistance and reusability. Our work provides new insights to the design of underwater biomimetic intelligent actuators based on photochemically transformation. Isotropic polyurethane hydrogels containing the dynamic covalent units hexaarylbiimidazole (HABI) are designed as visible light-driven anisotropic underwater actuators, which exhibit simple bending, diversified three-dimensional (3D) movement including curling, twisting and folding and the blooming/closing of biomimetic flower as well as the rolling of hydrogel wheel upon directional 405 nm irradiation. • Dual-crosslinked biomimetic polyurethane (PU) hydrogels containing hexaarylbiimidazole (HABI) units are fabricated. • The cleavage of dynamic C‒N bonds in HABI units cause the photo-induced secondary swelling of hydrogels upon irradiation. • Diversified three-dimensional (3D) deformation can be spatiotemporally programmed and achieved within tens of seconds. • The covalent-crosslinked dual networks endow actuators remarkable mechanical stability and long-term repeatable utility.

A Light-Driven Vibrotactile Actuator with a Polymer Bimorph Film for Localized Haptic Rendering.

A vibrotactile actuator driven by light energy is developed to produce dynamic stimulations for haptic rendering on a thin-film structure. The actuator is constructed by adopting a thermal bimorph membrane structure of poly(3,4-ethylenedioxythiophene) doped with p-toluenesulfonate (PEDOT-Tos) coated onto a polyethylene terephthalate (PET) film. Upon irradiation of near-infrared (NIR) light, the light energy absorbed at the PEDOT-Tos layer is converted into thermoelastic bending deformation due to the mismatch in coefficient of thermal expansion between PEDOT-Tos and PET. Since the light-induced deformation is reversible, spatially localized, and rapidly controllable with designed light signals, the proposed actuator can produce vibrotactile stimulation over 10 dB at arbitrary areas in the human-sensitive frequency range from 125 to 300 Hz using a low input power of ∼2.6 mW mm-2, as compared with a complex electrical circuit and high input power needed to achieve such actuation performance. Together with its simple structure based on light-driven actuation, the advent of this actuator could open up new ways to achieve substantial advances in rendering textures at a flexible touch interface.

Multimaterial Printing for Cephalopod-Inspired Light-Responsive Artificial Chromatophores.

Cephalopods use chromatophores distributed on their soft skin to change skin color and its pattern. Each chromatophore consists of a central sac containing pigment granules and radial muscles surrounding the sac. The contraction of the radial muscle causes the central sac to expand in area, making the color of the pigment more visible. With the chromatophores actuating individually, cephalopods can create extremely complex skin color patterns, which they utilize for exquisite functions including camouflage and communication. Inspired by this mechanism, we present an artificial chromatophore that can modulate its color pattern in response to light. Multimaterial projection microstereolithography is used to integrate three functional components including a photoactive hydrogel composite with polydopamine nanoparticles (PDA-NPs), acrylic acid hydrogel, and poly(ethylene glycol) diacrylate. In order to generate light-driven actuation of the artificial chromatophore, the photothermal effect of the PDA-NPs, light-responsive deformation of the photoactive hydrogel composite, and the produced mechanical stresses are studied. Mechanical properties and interfacial bonding strengths between different materials are also investigated to ensure structural integrity during actuation. We demonstrate pattern modulation of the light-responsive artificial chromatophores (LACs) with the projection of different light patterns. The LAC may suggest a new concept for various engineering applications such as the camouflage interface, biophotonic device, and flexible display.

Light-driven bimorph soft actuators: design, fabrication, and properties.

Soft robots that can move like living organisms and adapt to their surroundings are currently in the limelight from fundamental studies to technological applications, due to their advances in material flexibility, human-friendly interaction, and biological adaptation that surpass conventional rigid machines. Light-fueled smart actuators based on responsive soft materials are considered to be one of the most promising candidates to promote the field of untethered soft robotics, thereby attracting considerable attention amongst materials scientists and microroboticists to investigate photomechanics, photoswitch, bioinspired design, and actuation realization. In this review, we discuss the recent state-of-the-art advances in light-driven bimorph soft actuators, with the focus on bilayer strategy, i.e., integration between photoactive and passive layers within a single material system. Bilayer structures can endow soft actuators with unprecedented features such as ultrasensitivity, programmability, superior compatibility, robustness, and sophistication in controllability. We begin with an explanation about the working principle of bimorph soft actuators and introduction of a synthesis pathway toward light-responsive materials for soft robotics. Then, photothermal and photochemical bimorph soft actuators are sequentially introduced, with an emphasis on the design strategy, actuation performance, underlying mechanism, and emerging applications. Finally, this review is concluded with a perspective on the existing challenges and future opportunities in this nascent research Frontier.

Light-driven untethered soft actuators based on biomimetic microstructure arrays

Soft actuators based on smart materials and structures that can perform more diverse tasks skillfully, are being intensively sought. Despite the good progress made in the past few years, locomotion and transportation functionalities of the untethered soft-bodied devices for various natural terrains remain challenging. Inspired by a gecko crawling system, an untethered soft actuator with the abilities of picking up, transporting, and delivering objects controlled by NIR light is proposed. The soft actuator consisting of photo-responsive MWCNTs units and mushroom shaped microstructures, was fabricated by an integrative soft-lithography method with inking and imprinting processes. The integrated MWCNTs unit can convert NIR light irradiation into thermal energy, which can make the body of the soft actuator generate a strong shape deformation intrinsically in a self-contained way, leading to a combined discontinuous and continuous locomotion. Moreover, the integrated mushroom shaped microstructures can also realize grasping and manipulation of the object that was not constrained by the object's shapes and sizes, which was further addressed from experimental and theoretical perspectives. Thus, the combined use of smart materials and structures opens up new research avenues and represents a step forward toward future applications of light-driven untethered soft actuators.

Recent advances in the photothermal applications of two-dimensional nanomaterials: photothermal therapy and beyond

The photothermal applications of 2D nanomaterials in photothermal therapy, water evaporation, thermochemical reactions, light-driven actuators, photothermal electrodes, energy storage, wearable heaters and bacterial inhibition.