Capacitive and faradic charge components in high-speed carbon nanotube actuator

In vivo closed-loop control of a locust's leg using nerve stimulation

Activity of an innervated tissue can be modulated based on an acquired biomarker through feedback loops. How to convert this biomarker into a meaningful stimulation pattern is still a topic of intensive research. In this article, we present a simple closed-loop mechanism to control the mean angle of a locust’s leg in real time by modulating the frequency of the stimulation on its extensor motor nerve. The nerve is interfaced with a custom-designed cuff electrode and the feedback loop is implemented online with a proportional control algorithm, which runs solely on a microcontroller without the need of an external computer. The results show that the system can be controlled with a single-input, single-output feedback loop. The model described in this article can serve as a primer for young researchers to learn about neural control in biological systems before applying these concepts in advanced systems. We expect that the approach can be advanced to achieve control over more complex movements by increasing the number of recorded biomarkers and selective stimulation units.

Electroactive macromolecular motors as model materials of ectotherm muscles

The electrochemical reaction in liquid electrolytes of conducting polymers, carbon nanotubes, graphenes, among other materials, replicates the active components (macromolecular electro-chemical motors, ions and solvent) and volume variation of the sarcomere in any natural muscles during actuation, allowing the development of electro-chemo-mechanical artificial muscles. Materials, reactions and artificial muscles have been used as model materials, model reactions and model devices of the muscles from ectotherm animals. We present in this perspective the experimental results and a quantitative description of the thermal influence on the reaction extension and energetic achievements of those muscular models using different experimental methodologies. By raising the temperature for 40 °C keeping the extension of the muscular movement the cooperative actuation of the macromolecular motors harvest, saving chemical energy, up to 60% of the reaction energy from the thermal environment. The synergic thermal influence on either, the reaction rate (Arrhenius), the conformational movement rates of the motors (ESCR model) and the diffusion coefficients of ions across polymer matrix (WLF equation) can support the physical chemical foundations for the selection by nature of ectotherm muscles. Macromolecular motors act, simultaneously, as electro-chemo-mechanical and thermo-mechanical transducers. Technological and biological perspectives are presented.

Carbon Nanostructures for Actuators: An Overview of Recent Developments

In recent decades, micro and nanoscale technologies have become cutting-edge frontiers in material science and device developments. This worldwide trend has induced further improvements in actuator production with enhanced performance. A main role has been played by nanostructured carbon-based materials, i.e., carbon nanotubes and graphene, due to their intrinsic properties and easy functionalization. Moreover, the nanoscale decoration of these materials has led to the design of doped and decorated carbon-based devices effectively used as actuators incorporating metals and metal-based structures. This review provides an overview and discussion of the overall process for producing AC actuators using nanostructured, doped, and decorated carbon materials. It highlights the differences and common aspects that make carbon materials one of the most promising resources in the field of actuators.

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.

Diameter and density control of single-walled carbon nanotube forests by modulating Ostwald ripening through decoupling the catalyst formation and growth processes

A continuous and wide range control of the diameter (1.9-3.2 nm) and density (0.03-0.11 g cm(-3) ) of single-walled carbon nanotube (SWNT) forests is demonstrated by decoupling the catalyst formation and SWNT growth processes. Specifically, by managing the catalyst formation temperature and H2 exposure, the redistribution of the Fe catalyst thin film into nanoparticles is controlled while a fixed growth condition preserved the growth yield. The diameter and density are inversely correlated, where low/high density forests would consist of large/small diameter SWNTs, which is proposed as a general rule for the structural control of SWNT forests. The catalyst formation process is modeled by considering the competing processes, Ostwald ripening, and subsurface diffusion, where the dominant mechanism is found to be Ostwald ripening. Specifically, H2 exposure increases catalyst surface energy and decreases diameter, while increased temperature leads to increased diffusion on the surface and an increase in diameter.