True Low‐Power Self‐Locking Soft Actuators

Natural double‐layered structures observed in living organisms are known to exhibit asymmetric volume changes with environmental triggers. Typical examples are natural roots of plants, which show unique self‐organized bending behavior in response to environmental stimuli. Herein, light‐ and electro‐active polymer (LEAP) based actuators with a double‐layered structure are reported. The LEAP actuators exhibit an improvement of 250% in displacement and hold an object three times heavier as compared to that in the case of conventional electro‐active polymer actuators. Most interestingly, the bending motion of the LEAP actuators can be effectively locked for a few tens of minutes even in the absence of a power supply. Further, the self‐locking LEAP actuators show a large and reversible bending strain of more than 2.0% and require only 6.2 mW h cm^?2 of energy to hold an object for 15 min at an operating voltage of 3 V. These novel self‐locking soft actuators should find wide applicability in artificial muscles, biomedical microdevices, and various innovative soft robot technologies.     

High‐Resolution SPECT Imaging of Stimuli‐Responsive Soft Microrobots

Untethered small‐scale robots have great potential for biomedical applications. However, critical barriers to effective translation of these miniaturized machines into clinical practice exist. High resolution tracking and imaging in vivo is one of the barriers that limit the use of micro‐ and nanorobots in clinical applications. Here, the inclusion of radioactive compounds in soft thermoresponsive magnetic microrobots is investigated to enable their single‐photon emission computed tomography imaging. Four microrobotic platforms differing in hydrogel structure and four ^99mTc[Tc]‐based radioactive compounds are investigated in order to achieve optimal contrast agent retention and optimal imaging. Single microrobot imaging of structures as low as 100 µm in diameter, as well as tracking of shape switching from tubular to planar configurations by inclusion of ^99mTc[Tc] colloid in the hydrogel structure, is reported.     

Soft Actuators for Small‐Scale Robotics

This review comprises a detailed survey of ongoing methodologies for soft actuators, highlighting approaches suitable for nanometer‐ to centimeter‐scale robotic applications. Soft robots present a special design challenge in that their actuation and sensing mechanisms are often highly integrated with the robot body and overall functionality. When less than a centimeter, they belong to an even more special subcategory of robots or devices, in that they often lack on‐board power, sensing, computation, and control. Soft, active materials are particularly well suited for this task, with a wide range of stimulants and a number of impressive examples, demonstrating large deformations, high motion complexities, and varied multifunctionality. Recent research includes both the development of new materials and composites, as well as novel implementations leveraging the unique properties of soft materials.     

High‐Performance Hierarchical Black‐Phosphorous‐Based Soft Electrochemical Actuators in Bioinspired Applications

Bioinspired methods allowing artificial actuators to perform controllably are potentially important for various principles and may offer fundamental insight into chemistry and engineering. To date, the main challenges persist regarding the achievement of large deformation in fast response‐time and potential‐engineering applications in which electrode materials and structures limit ion diffusion and accumulation processes. Herein, a novel electrochemical actuator is developed that presents both higher electromechanical performances and biomimetic applications based on hierachically structured covalently bridged black phosphorous/carbon nanotubes. The new actuator demonstrates astonishing actuation properties, including low power consumption/strain (0.04 W cm^?2 %^?1), a large peak‐to‐peak strain (1.67%), a controlled frequency response (0.1–20 Hz), faster strain and stress rates (11.57% s^?1; 28.48 MPa s^?1), high power (29.11 kW m^?3), and energy (8.48 kJ m^?3) densities, and excellent cycling stability (500 000 cycles). More importantly, bioinspired applications such as artificial‐claw, wings‐vibrating, bionic‐flower, and hand actuators have been realized. The key to high performances stems from hierachically structured materials with an ordered lamellar structure, large redox activity, and electrochemical capacitance (321.4 F g^?1) for ions with smooth diffusion and flooding accommodation, which will guide substantial progress of next‐generation electrochemical actuators.     

State‐of‐the‐Art Analytical Methods for Assessing Dynamic Bonding Soft Matter Materials

Dynamic bonding materials are of high interest in a variety of fields in material science. The reversible nature of certain reaction classes is frequently employed for introducing key material properties such as the capability to self‐heal. In addition to the synthetic effort required for designing such materials, their analysis is a highly complex—yet important—endeavor. Herein, we critically review the current state of the art analytical methods and their application in the context of reversible bonding on demand soft matter material characterization for an in‐depth performance assessment. The main analytical focus lies on the characterization at the molecular level.     

Increasing the Dimensionality of Soft Microstructures through Injection‐Induced Self‐Folding

Devices fabricated using soft materials have been a major research focus of late, capturing the attention of scientists and laypersons alike in a wide range of fields, from microfluidics to robotics. The functionality of such devices relies on their structural and material properties; thus, the fabrication method is of utmost importance. Here, multilayer soft lithography, precision laser micromachining, and folding to establish a new paradigm are combined for creating 3D soft microstructures and devices. Phase‐changing materials are exploited to transform actuators into structural elements, allowing 2D laminates to evolve into a third spatial dimension. To illustrate the capabilities of this new fabrication paradigm, the first “microfluidic origami for reconfigurable pneumatic/hydraulic” device is designed and manufactured: a 12‐layer soft robotic peacock spider with embedded microfluidic circuitry and actuatable features.     

Model‐Free Rheo‐AFM Probes the Viscoelasticity of Tunable DNA Soft Colloids

Atomic force microscopy rheological measurements (Rheo‐AFM) of the linear viscoelastic properties of single, charged colloids having a star‐like architecture with a hard core and an extended, deformable double‐stranded DNA (dsDNA) corona dispersed in aqueous saline solutions are reported. This is achieved by analyzing indentation and relaxation experiments performed on individual colloidal particles by means of a novel model‐free Fourier transform method that allows a direct evaluation of the frequency‐dependent linear viscoelastic moduli of the system under investigation. The method provides results that are consistent with those obtained via a conventional fitting procedure of the force‐relaxation curves based on a modified Maxwell model. The outcomes show a pronounced softening of the dsDNA colloids, which is described by an exponential decay of both the Young's and the storage modulus as a function of the salt concentration within the dispersing medium. The strong softening is related to a critical reduction of the size of the dsDNA corona, down to ≈70% of its size in a salt‐free solution. This can be correlated to significant topological changes of the dense star‐like polyelectrolyte forming the corona, which are induced by variations in the density profile of the counterions. Similarly, a significant reduction of the stiffness is obtained by increasing the length of the dsDNA chains, which we attribute to a reduction of the DNA density in the outer region of the corona.