Remote Actuation Research Articles

Laser‐Induced Graphene Tapes as Origami and Stick‐On Labels for Photothermal Manipulation via Marangoni Effect

AbstractDirect light‐to‐work conversion enables remote actuation through a non‐contact manner, among which the photothermal Marangoni effect is significant for developing light‐driven robots because of the diversity of applicable photothermal materials and light sources, as well as the high energy conversion efficiency. However, the lack of nanotechnologies that enable flexible integration of advanced photothermal materials with actuators of complex configurations significantly restricts their practical applications. In this paper, laser‐induced graphene (LIG) tape is reported as stick‐on photothermal labels for developing light‐driven actuators based on the Marangoni effect. With the help of direct laser writing technology, graphene patterns with superior photothermal properties are prepared on the PI tape. The patterned LIG tape can be stuck on any desired objects and generates an asymmetric photothermal field under light irradiation, forming a photothermal Marangoni actuator. Additionally, the PI tape with LIG patterns can be folded into 3D origami actuators that permit photothermal Marangoni actuation including both translation and rotation. The graphene‐based photothermal Marangoni actuators feature biocompatibility, which is confirmed by MDA‐MB‐231 cells proliferation experiments. Owing to the excellent photothermal property of LIG patterns, the as‐produced photothermal actuators can be manipulated by a variety of light sources, holding great promise for developing light‐driven soft robots.

Magnetic Actuation With Stationary Electromagnets Considering Power and Temperature Constraints

In systems comprising stationary electromagnets designed for magnetic manipulation and remote magnetic actuation, the standard method for achieving some desired system output (e.g., magnetic force and torque) is to form a matrix that maps the electromagnets’ electrical currents to the resulting output, and then use the pseudoinverse of that matrix to solve for the currents. However, this method does not account for the nonlinear nature of the saturation limits of the amplifiers and power supply, nor does it account for the temperature in the electromagnets, both of which limit the system's overall performance in practice. In this letter, we propose improved current-solving methods that account for these real-world system limitations. We demonstrate how the performance of systems can be improved by increasing both the achievable output magnitudes and the total operating time to achieve those outputs, and how the risk of overheating can be eliminated.

A Review of Shape Memory Polymers and Composites: Mechanisms, Materials, and Applications.

Over the past decades, interest in shape memory polymers (SMPs) has persisted, and immense efforts have been dedicated to developing SMPs and their multifunctional composites. As a class of stimuli-responsive polymers, SMPs can return to their initial shape from a programmed temporary shape under external stimuli, such as light, heat, magnetism, and electricity. The introduction of functional materials and nanostructures results in shape memory polymer composites (SMPCs) with large recoverable deformation, enhanced mechanical properties, and controllable remote actuation. Because of these unique features, SMPCs have a broad application prospect in many fields covering aerospace engineering, biomedical devices, flexible electronics, soft robotics, shape memory arrays, and 4D printing. Herein, a comprehensive analysis of the shape recovery mechanisms, multifunctionality, applications, and recent advances in SMPs and SMPCs is presented. Specifically, the combination of functional, reversible, multiple, and controllable shape recovery processes is discussed. Further, established products from such materials are highlighted. Finally, potential directions for the future advancement of SMPs are proposed.

Parallelized Manipulation of Adherent Living Cells by Magnetic Nanoparticles-Mediated Forces

The remote actuation of cellular processes such as migration or neuronal outgrowth is a challenge for future therapeutic applications in regenerative medicine. Among the different methods that have been proposed, the use of magnetic nanoparticles appears to be promising, since magnetic fields can act at a distance without interactions with the surrounding biological system. To control biological processes at a subcellular spatial resolution, magnetic nanoparticles can be used either to induce biochemical reactions locally or to apply forces on different elements of the cell. Here, we show that cell migration and neurite outgrowth can be directed by the forces produced by a switchable parallelized array of micro-magnetic pillars, following the passive uptake of nanoparticles. Using live cell imaging, we first demonstrate that adherent cell migration can be biased toward magnetic pillars and that cells can be reversibly trapped onto these pillars. Second, using differentiated neuronal cells we were able to induce events of neurite outgrowth in the direction of the pillars without impending cell viability. Our results show that the range of forces applied needs to be adapted precisely to the cellular process under consideration. We propose that cellular actuation is the result of the force on the plasma membrane caused by magnetically filled endo-compartments, which exert a pulling force on the cell periphery.

MagWorm: A Biomimetic Magnet Embedded Worm-Like Soft Robot.

Emerging worm-like soft robots with various soft materials and different actuation mechanism have been frequently discussed. It is very challenging for soft robots in realizing a fast and untethered crawling. In this article, a biomimetic magnet embedded worm-like robot (shorted as "MagWorm") in the size of centimeter level is designed and investigated. The actuation of the MagWorm is achieved by housing permanent magnetic patches in its soft body, which interact with an external moving drive-magnet system. A dynamic model is established, coupling the discrete elastic rod model with magnetic actuation. The driving mechanism is then numerically studied. Quantitative comparisons between the numerical solution and experiment results show reasonable agreement. It is shown that the MagWorm can deform part of its body into a "Ω" shape and generate biomimetic crawling locomotion. The crawling speed of the robot is studied experimentally with different sizes. Some potential applications are also proposed and demonstrated. The MagWorm represents compact and low-cost solutions that use permanent magnets for remote actuation of soft robot and can be continuously operated during long procedures.

Effect of gold and graphene oxide nanoparticles on the thermo- and photo-actuation of monodomain liquid crystal elastomers

Monodomain liquid crystal elastomers (m-LCEs) were synthesized from polymethylhydrosiloxane (PMHS), two distinct vinyl-functionalized mesogens (benzoate and azobenzene) and one crosslinking monomer, using the hydrosilylation reaction. Gold or amino-functionalized graphene oxide nanoparticles (NP) were in-situ incorporated into the m-LCEs, aiming to enhance their response to thermal and optical stimuli. All m-LCEs exhibited a degradation temperature of ~310 °C and a mesomorphic behavior over a wide temperature range (clearing temperature around 100 °C). The inclusion of nanoparticles stiffened the m-LCEs, although they induced a highly randomized ordering of mesogens at the nematic to isotropic transition, resulting in a higher specimen contraction; a schematic model is proposed in this concern. The photo-actuation (bending) of the m-LCEs/NP composites resulted rather diminished as they became stiffer than the neat m-LCEs, although the increasing content of azobenzene units allowed higher bending angles that could be suitable for remote actuation applications.

Acoustic Vibration‐Induced Actuation of Multiple Microrotors in Microfluidics

AbstractSimultaneous and uniform actuation of multiple microrotors with easy fabrication method has been gathering significant attention in the field of precise microfluidic manipulation. In this work, the use of a piezoelectric vibration stage is presented to achieve the tunable acoustic vibration‐induced actuation of multiple microrotors fabricated by two‐photon polymerization. A series of curved sharp tips are predefined on the microrotors, which can generate paired asymmetric acoustic microstreaming to propel the rotor rotating around the stator with <1 kHz acoustic vibration. Microrotor's rotational speed can be readily controlled by tuning the signal input frequency and the number of rotor arms. A rotational speed of ≈1600 RPM can be achieved by a series of microrotors in aqueous solutions. This method enables easy and versatile microrotor fabrication and remote actuation of multiple rotors with simplicity and uniformity, providing promising solutions in various microfluidic manipulation applications.

Encoding multiple permanent shapes in 3D printed structures

Conventional methods of programmed shape change in polymers are one-way and one-time only. We introduce a new method of combining a bioinspired, hierarchical architecture with the pre-strain generated by extrusion-based 3D printing to encode multiple permanent shapes in thermoplastic polymer shell structures. At high temperature, these structures are multistable and can snap repeatedly between all encoded permanent shapes without reprogramming. At low temperature, the structures are monostable with increased stiffness; the multistability can be switched on and off via temperature. Characterization studies are performed to determine how to control the level of pre-strain and the deflection behavior of the structure to enable finite element modeling for analysis and design. This pre-straining technique may be thought of as a virtual mold: printed structures are initially flat but have multiple permanent shapes encoded. Taking advantage of the geometric freedom of 3D printing, complex geometries, and pre-strain fields may be used to create highly tailored snapping structures. Thermoplastic filaments with added particles may be used to impart additional multifunctionality to the structures, such as magnetic responsiveness, to enable remote actuation. These switchable multistable structures have potential applications in fields including robotics, aerospace, and smart buildings.

Ultra-High Actuation Stress Polymer Actuators as Light-Driven Artificial Muscles.

Remotely addressable actuators are of great interest in fields like microrobotics and smart textiles because of their simplicity, integrity, flexibility, and lightweight. However, most of the existing actuator systems are composed of complex assemblies and/or offer a low response rate. Here, the actuation performance of a light-driven, highly oriented film based on ultra-high molecular weight polyethylene (UHMW-PE), containing a photo-responsive additive, 2-(2H-benzotriazol-2-yl)-4,6-ditertpentylphenol (BZT), is reported. The material exhibits a fast (<1 s) and reversible photo-induced thermal response upon exposure to UV light, which results in an exceptionally high actuation stress (∼70 MPa) at a low strain (<0.1%). The proposed actuation mechanism originates from light absorption by BZT and energy transfer into heat, in combination with the intrinsic high stiffness (∼80 GPa) and a negative thermal expansion (NTE) of the oriented polymer films. This unique set of properties of this actuator, in particular the very high specific actuation stress, compared to existing organic and inorganic actuators, and the remote optical actuation, promises impact in fields related to soft robotics, composites, medical devices, optics, prosthetics, and smart textiles.

Magnetic Actuation Systems for Miniature Robots: A Review

A magnetic field, which is transparent and relatively safe to biological tissue, is a powerful tool for remote actuation and wireless control of magnetic devices. Furthermore, miniature robots can access complex and narrow regions of the human body as well as manipulate down to subcellular entities; however, integrating onboard components is difficult due to their limited size. Combining these two technologies, magnetic miniature robots have undergone rapid development during the past two decades, mainly because of their high potential in medical and bioengineering applications. To improve the scientific and clinical outcomes of these tiny agents, developing suitable and reliable actuation systems is essential. As a newly emerging field that has progressed in recent years, magnetic actuation systems offer a harmless and effective approach for the remote control of miniature robots via a dynamic magnetic field. Herein, a review on the state‐of‐the‐art magnetic actuation systems for miniature robots is presented with the goal of providing readers with a better understanding of magnetic actuation and guidance for future system design.

Ultrasound-Guided Wireless Tubular Robotic Anchoring System.

Untethered miniature robots have significant poten-tial and promise in diverse minimally invasive medical applications inside the human body. For drug delivery and physical contra-ception applications inside tubular structures, it is desirable to have a miniature anchoring robot with self-locking mechanism at a target tubular region. Moreover, the behavior of this robot should be tracked and feedback-controlled by a medical imaging-based system. While such a system is unavailable, we report a reversible untethered anchoring robot design based on remote magnetic actuation. The current robot prototype's dimension is 7.5 mm in diameter, 17.8 mm in length, and made of soft polyurethane elastomer, photopolymer, and two tiny permanent magnets. Its relaxation and anchoring states can be maintained in a stable manner without supplying any control and actuation input. To control the robot's locomotion, we implement a two-dimensional (2D) ultrasound imaging-based tracking and control system, which automatically sweeps locally and updates the robot's position. With such a system, we demonstrate that the robot can be controlled to follow a pre-defined 1D path with the maximal position error of 0.53 ± 0.05 mm inside a tubular phantom, where the reversible anchoring could be achieved under the monitoring of ultrasound imaging.

Fully Wearable Actuated Soft Exoskeleton for Grasping Assistance in Everyday Activities.

Worldwide, over 50 million people suffer from persistent hand impairments after stroke or spinal cord injury (SCI). This results in major loss of independence and quality of life. Robotic hand exoskeletons can compensate for lost motor function and assist in grasping tasks performed in everyday activities. Several recent prototypes can partially provide this assistance. However, it remains challenging to integrate the dexterity required for daily tasks in a safe and user-friendly design that is acceptable for daily use in subjects with neuromotor hand impairments. We present the design of RELab tenoexo; a fully wearable assistive soft hand exoskeleton for daily activities. We present sleek mechanisms for a hand module that generates the four most frequently used grasp types, employing a remote actuation system that reduces weight on the hand. For optimal assistance and highest adaptability, we present various design and control options to customize the modular device, along with an automated tailoring algorithm that allows automatically generated hand modules for individual users. Mechanical evaluation shows that RELab tenoexo covers the range of motion and the fingertip forces required to assist users in up to 80% of all grasping activities. In user tests, we find that the low weight, unintrusive size, high wearing comfort, and appealing appearance are beneficial for user acceptance and usability in daily life. Finally, we demonstrate that RELab tenoexo leads to an immediate improvement of the functional grasping ability in a subject with SCI.

Rapid remote actuation in shape memory hyperbranched polyurethane composites using cross-linked photothermal reduced graphene oxide networks

We report near-infrared (NIR) laser-driven rapid shape recovery in hyperbranched polyurethane/epoxy (HBPU/EP) composites based on cross-linked graphene photothermal networks. Graphene-based photothermal reinforcements were synthesized by functionalizing graphene oxide (GO) with the epoxy bisphenol A diglycidil ether (DGEBA) to form DGEBA-f-GO, and by subsequent reduction of DGEBA-f-GO to DGEBA-f-reduced graphene oxide (DGEBA-f-rGO). Upon irradiation with an 808 nm NIR laser, the composites with 1 wt% cross-linked DGEBA-f-rGO exhibited a remarkable shape recovery time of 6.5 s (one-fourth that of the composites with 1 wt% GO). The rapid actuation in these composites results from excellent photothermal conversion by the cross-linked DGEBA-f-rGO owing to enhanced π conjugation in rGO and homogeneous dispersion of graphene networks in the polymer matrix due to covalent interactions. An increase in the epoxy groups on the GO surface also enhanced the mechanical properties of the composites by forming denser cross-linked networks. Graphene-based photothermal networks may be suitable for fabricating robust and remote-controllable rapid shape recovery composites.

Functionalizing Double-Network Hydrogels for Applications in Remote Actuation and in Low-Temperature Strain Sensing.

Multifunctional hydrogels have important applications in various fields such as artificial muscles, wearable devices, soft robotics, and tissue engineering, especially for those with favorable mechanical properties, good low-temperature resistance, and stimuli-responsive capabilities. In the current study, a type of polyacrylamide/sodium alginate/carbon nanotube (PAAm/SA/CNT) double-network (DN) hydrogel was fabricated, which exhibited a high tensile strength of 271.68 ± 6.04 kPa, a favorable conductivity of 1.38 ± 0.17 S·m-1, and a good self-healing ability under heating conditions. In addition, the composite hydrogel exhibited controllable photomechanical deformations under near-infrared irradiation, such as bending, swelling, swimming, and object grasping. To further broaden the applications of the hydrogel in low-temperature environments, calcium chloride (CaCl2) was introduced into such a PAAm/SA/CNT DN hydrogel as an additive. Interestingly, the tensile/compressive strengths as well as elasticity were well-maintained at a temperature as low as -20 °C. In addition, the PAAm/SA/CNT/CaCl2 hydrogel presented excellent conductivity, recoverability, and strain-sensing capability under such extreme conditions. Overall, the investigations conducted in this paper have provided potentially new methods and inspirations for the generation of multifunctional PAAm/SA/CNT/CaCl2 hybrid DN hydrogels toward extended applications.

Reprogrammable Ferromagnetic Domains for Reconfigurable Soft Magnetic Actuators.

Soft magnetic materials have shown promise in diverse applications due to their fast response, remote actuation, and large penetration range for various conditions. Herein, a new soft magnetic composite material capable of reprogramming its magnetization profile without changing intrinsic magnetic properties of embedded magnetic particles or the molecular property of base material is reported. This composite contains magnetic microspheres in an elastomeric matrix, and the magnetic microspheres are composed of ferromagnetic microparticles encapsulated with oligomeric-PEG. By controlling the encapsulating polymer phase transition, the magnetization profiles of the magnetic composite can be rewritten by physically realigning the ferromagnetic particles. Diverse magnetic actuators with reprogrammable magnetization profiles are developed to demonstrate the complete reprogramming of complex magnetization profile.

A Fully Actuated Body-Mounted Robotic Assistant for MRI-Guided Low Back Pain Injection.

This paper reports the development of a fully actuated body-mounted robotic assistant for MRI-guided low back pain injection. The robot is designed with a 4-DOF needle alignment module and a 2-DOF remotely actuated needle driver module. The 6-DOF fully actuated robot can operate inside the scanner bore during imaging; hence, minimizing the need of moving the patient in or out of the scanner during the procedure, and thus potentially reducing the procedure time and streamlining the workflow. The robot is built with a lightweight and compact structure that can be attached directly to the patient's lower back using straps; therefore, attenuating the effect of patient motion by moving with the patient. The novel remote actuation design of the needle driver module with beaded chain transmission can reduce the weight and profile on the patient, as well as minimize the imaging degradation caused by the actuation electronics. The free space positioning accuracy of the system was evaluated with an optical tracking system, demonstrating the mean absolute errors (MAE) of the tip position to be 0.99±0.46 mm and orientation to be 0.99±0.65°. Qualitative imaging quality evaluation was performed on a human volunteer, revealing minimal visible image degradation that should not affect the procedure. The mounting stability of the system was assessed on a human volunteer, indicating the 3D position variation of target movement with respect to the robot frame to be less than 0.7 mm.

Multicolor 4D printing of shape-memory polymers for light-induced selective heating and remote actuation

Four-dimensional (4D) printing can add active and responsive functions to three-dimensional (3D) printed objects in response to various external stimuli. Light, among others, has a unique advantage of remotely controlling structural changes to obtain predesigned shapes. In this study, we demonstrate multicolor 4D printing of shape-memory polymers (SMPs). Using color-dependent selective light absorption and heating in multicolor SMP composites, we realize remote actuation with light illumination. We experimentally investigate the temperature changes in colored SMPs and observe a clear difference between the different colors. We also present simulations and analytical calculations to theoretically model the structural variations in multicolor composites. Finally, we consider a multicolor hinged structure and demonstrate the multistep actuation by changing the color of light and duration of illumination. 4D printing can allow complex, multicolor geometries with predesigned responses. Moreover, SMPs can be reused multiple times for thermal actuation by simply conducting thermomechanical programming again. Therefore, 4D printing of multicolor SMP composites have unique merits for light-induced structural changes. Our study indicates that multicolor 4D printing of SMPs are promising for various structural changes and remote actuation.

Magnetic and Conductive Liquid Metal Gels.

Liquid metals are fast becoming a new class of universal and frictionless additives for the development of multifunctional soft and flexible materials. Herein, nanodroplets of eutectic gallium-indium alloy, which is liquid at room temperature, were used as a platform for the formulation of electrically conductive and magnetically responsive gels with the incorporation of Fe3O4 nanoparticles. The nanoadditives were prepared in situ within a water-based solution of polyvinyl alcohol. A borax cross-linking reaction was then performed to yield multifunctional flexible and self-healing gels. The physicochemical properties and changes in the nanoadditives at each step of the gel preparation method were characterized. Oxidation and complexation reactions between the liquid metal and iron oxide nanoadditives were observed. A mixture of nanosized functional magnetic Fe3O4/Fe2O3 and In-Fe oxide complexes was found to enable the magnetic susceptibility of the gels. The mechanical and self-healing properties of the gels were assessed, and finally, this flexible and multifunctional material was used as an electronic switch via remote magnetic actuation. The developed conductive and magnetic gels demonstrate great potential for the design of soft electronic systems.

Cover Feature: Remote Actuation of a Light‐Emitting Device Based on Magnetic Stirring and Wireless Electrochemistry (ChemPhysChem 7/2020)

The Cover Feature shows a freestanding light-emitting diode (LED) that is addressed in a wireless manner by means of bipolar electrochemistry. Also, the tips of this electronic device are made out of iron enabling thus a magnetic stirring. The brightness of the LED can be readily used as an optical readout to monitor a chemical composition change in the electrolyte solution in real time. More information can be found in the Article by A. L. Dauphin et al.

Remote Actuation of a Light-Emitting Device Based on Magnetic Stirring and Wireless Electrochemistry.

We propose a straightforward access to a rotating light-emitting device powered by wireless electrochemistry. A magnetic stirrer is used to rotate a light-emitting diode (LED) due to the intrinsic magnetic properties of the tips that contain iron. At the same time, the LED is submitted to an electric field and acts as a bipolar electrode. The electrochemical processes that are coupled on both extremities of the LED drive an electron flow across the device, resulting in light emission. The variation of the LED alignment in time enables an alternating light emission that is directly controlled by the rotation rate. The stirring also enables a continuous mixing of the electrolyte that improves the stability of the output signal. Finally, the LED brightness can readily reveal a change of chemical composition in the electrolyte solution.