Plant-inspired rearrangement of liquid in a porous structure for controlled swelling.

Soft robots can adapt to dynamic environments without prior knowledge of their properties. Plants inspire mechanisms for counterbalancing dynamic loads by locally modulating compliance through anisotropic humidity-responsive materials and structures. In addition to well-known passive bilayers, plants may also actively control swelling. The combination of robust hygroscopic material-level response and simple electrical control makes active swelling particularly attractive for technological implementation. However, dynamic swelling demands the development and optimisation of congruent pumping solutions. This work suggests electrohydrodynamic pumping, enabled by highly reversible ion immobilisation at capacitive electrodes, as a particularly suitable low-pressure, high-area liquid displacement solution for active swelling. Local pore fill ratio (PFR) modulation is used as a measure for dynamic liquid displacement and swelling. A method for highly localised (10µm membrane thickness) assessment of the dynamic variation of PFR in a 400µm laminate undergoing cross-plane electrokinetic liquid displacement is developed. Two modes for transient PFR modulation were identified: electrokinetic ion transfer and diffusive solvent redistribution, pronounced at high and low voltage scan rates, respectively. The strategic combination of these modes enables various compliance-modulation scenarios. The system contains (within a cycle) a constant amount of liquid in an open network of liquid-filled pores. 30%-75% PFR yielded the highest dynamic PFR modulation: a high amount of empty pores is beneficial, yet a too-low PFR compromises the continuous liquid pathway necessary for electrokinetic pumping. The dynamic nature of internal liquid rearrangement was characterised by relatively fast electrokinetics-driven fluxes (6.3% PFR change in 80 s), followed by a slow equilibration of concentration and PFR. At high scan rates, PFR decreased at positive polarisation, while both positive and negative polarity yielded a similar decrease at low scan rates (5 mV s-1). Localised control over the swelling gradient enables the design of systems that morphologically adapt to complex dynamic loading conditions.

ROBOTONT - Open-source and ROS-supported omnidirectional mobile robot for education and research.

In order to achieve visionary concepts such as Society 5.0 and Industry 5.0, there is a growing need for people who are able to create innovative robotic technologies. Training students to become such skilled professionals requires transitioning from often toy-like educational platforms with significant hardware limitations to costly research robots with full ROS (Robot Operating System) support. To aid in this transition, we propose Robotont - an open-source omnidirectional mobile robot platform with both physical hardware and a digital twin. Robotont enables robotics education with professional tools as well as provides researchers with a capable mobility platform for validating and demonstrating scientific results. Robotont has successfully been used for university teaching, professional education, and online courses about ROS and robotics.

Dip-coating electromechanically active polymer actuators with SIBS from midblock-selective solvents to achieve full encapsulation for biomedical applications.

Soft and compliant ionic electromechanically active polymer actuators (IEAPs) are a promising class of smart materials for biomedical and soft robotics applications. These materials change their shape in response to external stimuli like the electrical signal. This shape-change results solely from the ion flux inside the composite and hence the material can be miniaturized below the centimeter and millimeter levels-something that still poses a challenge for many other conventional actuation mechanisms in soft robotics (e.g., pneumatic, hydraulic, or tendon-based systems). However, the components used to prepare IEAPs are typically not safe for the biological environment, nor is the environment safe for the actuator. Safety concerns and unreliable operation in foreign liquid environments have been some of the main obstacles for the widespread adoption of IEAPs in many areas, e.g., in biomedical applications. Here we show a novel approach to fully encapsulate IEAP actuators with the biocompatible block copolymer SIBS (poly(styrene-block-isobutylene-block-styrene)) dissolved in block-selective solvents. Reduction in the bending amplitude due to the added passive layers, a common negative side-effect of encapsulating IEAPs, was not observed in this work. In conclusion, the encapsulated actuator is steered through a tortuous vasculature mock-up filled with a viscous buffer solution mimicking biological fluids.

Scalable and heterogenous mobile robot fleet-based task automation in crowded hospital environments-a field test.

In hospitals, trained medical staff are often, in addition to performing complex procedures, spending valuable time on secondary tasks such as transporting samples and medical equipment; or even guiding patients and visitors around the premises. If these non-medical tasks were automated by deploying mobile service robots, more time can be focused on treating patients or allowing well-deserved rest for the potentially overworked healthcare professionals. Automating such tasks requires a human-aware robotic mobility system that can among other things navigate the hallways of the hospital; predictively avoid collisions with humans and other dynamic obstacles; coordinate task distribution and area coverage within a fleet of robots and other IoT devices; and interact with the staff, patients and visitors in an intuitive way. This work presents the results, lessons-learned and the source code of deploying a heterogeneous mobile robot fleet at the Tartu University Hospital, performing object transportation tasks in areas of intense crowd movement and narrow hallways. The primary use-case is defined as transporting time-critical samples from an intensive care unit to the hospital lab. Our work builds upon Robotics Middleware Framework (RMF), an open source, actively growing and highly capable fleet management platform which is yet to reach full maturity. Thus this paper demonstrates and validates the real-world deployment of RMF in an hospital setting and describes the integration efforts.

Data on FTIR, photo-DSC and dynamic DSC of triethylene glycol dimethacrylate and N-vinylpyrrolidone copolymerization in the presence of ionic liquids.

Here we show the effect of the ionic liquid nature, its content and monomer/crosslinker ratio on the copolymerization of N-vinylpyrrolidone (NVP) with triethylene glycol dimethacrylate (TEGDMA) induced by UV or heat irradiation. For the first time, kinetics curves of photopolymerization NVP with TEGDMA in the presence of ionic liquids are obtained. The ionic liquids EmimBF4, BmimBF4, OmimBF4 and EmimTFSI with different cation and anion structures and lengths of the alkyl radical were varied in photopolymer compositions. To understand the influence of ionic liquids on the polymerization kinetics, photo-DSC, dynamic DSC, and FTIR were performed. Parameters obtained from photo-DSC curves allowed to develop the methodology for the stereolithography of ionogels. The presented data constitutes the complete dataset useful for 3D-printing of ionogels with high accuracy, which is reported in the main article.

Mechanism of Spontaneous Surface Modifications on Polycrystalline Cu Due to Electric Fields.

We present a credible mechanism of spontaneous field emitter formation in high electric field applications, such as Compact Linear Collider in CERN (The European Organization for Nuclear Research). Discovery of such phenomena opens new pathway to tame the highly destructive and performance limiting vacuum breakdown phenomena. Vacuum breakdowns in particle accelerators and other devices operating at high electric fields is a common problem in the operation of these devices. It has been proposed that the onset of vacuum breakdowns is associated with appearance of surface protrusions while the device is in operation under high electric field. Moreover, the breakdown tolerance of an electrode material was correlated with the type of lattice structure of the material. Although biased diffusion under field has been shown to cause growth of significantly field-enhancing tips starting from initial nm-size protrusions, the mechanisms and the dynamics of the growth of the latter have not been studied yet. In the current paper we conduct molecular dynamics simulations of nanocrystalline copper surfaces and show the possibility of protrusion growth under the stress exerted on the surface by an applied electrostatic field. We show the importance of grain boundaries on the protrusion formation and establish a linear relationship between the necessary electrostatic stress for protrusion formation and the temperature of the system. Finally, we show that the time for protrusion formation decreases with the applied electrostatic stress, we give the Arrhenius extrapolation to the case of lower fields, and we present a general discussion of the protrusion formation mechanisms in the case of polycrystalline copper surfaces.

An All-Textile Non-muscular Biomimetic Actuator Based on Electrohydrodynamic Swelling.

Mass transfer from one part of an organism to another constitutes a fundamental non-muscular movement strategy in living organisms, in particular in plants. The demonstrable simplicity and safety make non-muscular actuators especially attractive for distributed configurations such as in wearable robotic applications on a textile platform. However, practical arrangements for integrating actuators as inherent parts of textiles is an ongoing challenge. Here we demonstrate an electrohydrodynamic ionic actuator that combines two textiles of natural origin. The first textile - viscose-rayon-derived activated carbon cloth - consists of high-surface-area monolithic fibers that provide electrical and mechanical integrity, whereas the other textile - silk - contributes to mechanical integrity in the lateral direction while preventing the conductive textiles from contacting. By injecting an electronic charge into the activated carbon cloth electrodes, the migration of the electrolyte ions is initiated in the porous network in-between the electrodes, causing non-uniform swelling and eventually bending of the laminate. The three-layer laminate composed of integral textile fibers demonstrated a ∼0.8% strain difference. Electrical control over a fluid movement in a textile platform provides a scalable method for functional textiles not limited to actuation.

Dynamic coupling between particle-in-cell and atomistic simulations.

We propose a method to directly couple molecular dynamics, the finite element method, and particle-in-cell techniques to simulate metal surface response to high electric fields. We use this method to simulate the evolution of a field-emitting tip under thermal runaway by fully including the three-dimensional space-charge effects. We also present a comparison of the runaway process between two tip geometries of different widths. The results show with high statistical significance that in the case of sufficiently narrow field emitters, the thermal runaway occurs in cycles where intensive neutral evaporation alternates with cooling periods. The comparison with previous works shows that the evaporation rate in the regime of intensive evaporation is sufficient to ignite a plasma arc above the simulated field emitters.

Growth mechanism for nanotips in high electric fields.

In this work we show using atomistic simulations that the biased diffusion in high electric field gradients creates a mechanism whereby nanotips may start growing from small surface asperities. It has long been known that atoms on a metallic surface have biased diffusion if electric fields are applied and that microscopic tips may be sharpened using fields, but the exact mechanisms have not been well understood. Our Kinetic Monte Carlo simulation model uses a recently developed theory for how the migration barriers are affected by the presence of an electric field. All parameters of the model are physically motivated and no fitting parameters are used. The model has been validated by reproducing characteristic faceting patterns of tungsten surfaces that have in previous experiments been observed to only appear in the presence of strong electric fields. The growth effect is found to be enhanced by increasing fields and temperatures.

Fabrication of Carbon-Based Ionic Electromechanically Active Soft Actuators.

Ionic electromechanically active capacitive laminates are a type of smart material that move in response to electrical stimulation. Due to the soft, compliant and biomimetic nature of this deformation, actuators made of the laminate have received increasing interest in soft robotics and (bio)medical applications. However, methods to easily fabricate the active material in large (even industrial) quantities and with a high batch-to-batch and within-batch repeatability are needed to transfer the knowledge from laboratory to industry. This protocol describes a simple, industrially scalable and reproducible method for the fabrication of ionic carbon-based electromechanically active capacitive laminates and the preparation of actuators made thereof. The inclusion of a passive and chemically inert (insoluble) middle layer (e.g., a textile-reinforced polymer network or microporous Teflon) distinguishes the method from others. The protocol is divided into five steps: membrane preparation, electrode preparation, current collector attachment, cutting and shaping, and actuation. Following the protocol results in an active material that can, for example, compliantly grasp and hold a randomly shaped object as demonstrated in the article.

Influence of Carboxylate Anions on Phase Behavior of Choline Ionic Liquid Mixtures.

Mixing ionic liquids is a suitable strategy to tailor properties, e.g., to reduce melting points. The present study aims to widen the application range of low-toxic choline-based ionic liquids by studying eight binary phase diagrams of six different choline carboxylates. Five of them show eutectic points with melting points dropping by 13 to 45 °C. The eutectic mixtures of choline acetate and choline 2-methylbutarate were found to melt at 45 °C, which represents a remarkable melting point depression compared to the pure compounds with melting points of 81 (choline acetate) and 90 °C (choline 2-methylbutarate), respectively. Besides melting points, the thermal stabilities of the choline salt mixtures were investigated to define the thermal operation range for potential practical applications of these mixtures. Typical decomposition temperatures were found between 165 and 207 °C, with choline lactate exhibiting the highest thermal stability.

Low concentrated carbonaceous suspensions assisted with carboxymethyl cellulose as electrode for electrochemical flow capacitor.

The search for efficient energy storage devices has recently led to the introduction of a fluid electrode material employing electrochemical flow capacitors (EFC). Unlike the classical solid electrode film containing capacitors, where the electrode material is fixed to the current collectors and capacitance is therefore limited with an active surface area of porous electrode, the flow electrodes offer new design opportunities which enable fully continuous charging/discharging processes as well as easily scalable systems. Here we describe the successful incorporation of the carboxymethyl cellulose sodium salt (CMC-Na) assisted carbonaceous suspension electrode in aqueous media for the electrochemical flow capacitor concept and demonstrate the electrochemical charge storage in flowable electrodes using a cation conductive membrane as separator in a double-pipe flow-electrode module. Experimental results were combined with computer simulations (FEM) to specify limiting processes EFC charging. The flow-electrode slurry is based on 0.1 M Na2SO4, 3 wt% CMC-Na and activated carbon powder suspended in water. During continuous operation of the system, the capacitance of the flow electrode reached to 0.3 F/L providing the energy and current densities of 7 mWh/kg and 56 mW/L, respectively. Additionally, we report a 70% round trip efficiency calculated during charging and discharging of the cell between 0 V and +0.75 V, while applying the current density of 1.6 mA/kg. The double-pipe flow-electrode module is easily expandable for transportation of large volumes of electrode material.

Ionic Actuators as Manipulators for Microscopy.

Non-destructive handling of soft biological samples at the cellular level is becoming increasingly relevant in life sciences. In particular, spatially dense arrangements of soft manipulators with the capability of in situ monitoring via optical and electron microscopes promises new and exciting experimental techniques. The currently available manipulation technologies offer high positioning accuracy, yet these devices significantly grow in complexity in achieving compliance. We explore soft and compliant actuator material with a mechanical response similar to gel-like samples for perspective miniaturized manipulators. First, we demonstrate three techniques for rendering the bulk sheet-like electroactive material, the ionic and capacitive laminate (ICL), into a practical manipulator. We then show that these manipulators are also highly compatible with electron optics. Finally, we explore the performance of an ICL manipulator in handling a single large cell. Intrinsic compliance, miniature size, simple current-driven actuation, and negligible interference with the imaging technologies suggest a considerable perspective for the ICL in spatially dense arrays of compliant manipulators for microscopy.

Natural cellulose ionogels for soft artificial muscles.

Rapid development of soft micromanipulation techniques for human friendly electronics has raised the demand for the devices to be able to carry out mechanical work on a micro- and macroscale. The natural cellulose-based ionogels (CEL-iGEL) hold a great potential for soft artificial muscle application, due to its flexibility, low driving voltage and biocompatibility. The CEL-iGEL composites undergo reversible bending already at ±500mV step-voltage values. A fast response to the voltage applied and high ionic conductivity of membranous actuator is achieved by a complete dissolution of cellulose in 1-ethyl-3-methylimidazolium acetate [EMIm][OAc]. The CEL-iGEL supported cellulose actuator films were cast out of cellulose-[EMIm][OAc] solution via phase inversion in H2O. The facile preparation method ensured uniform morphology along the layers and stand for the high ionic-liquid loading in a porous cellulose scaffold. During the electromechanical characterization, the CEL-iGEL actuators showed exponential dependence to the voltage applied with the max strain difference values reaching up to 0.6% at 2 V. Electrochemical analysis confirmed the good stability of CEL-iGEL actuators and determined the safe working voltage value to be below 2.5V. To predict and estimate the deformation for various step input voltages, a mathematical model was proposed.

Au nanowire junction breakup through surface atom diffusion.

Metallic nanowires are known to break into shorter fragments due to the Rayleigh instability mechanism. This process is strongly accelerated at elevated temperatures and can completely hinder the functioning of nanowire-based devices like e.g. transparent conductive and flexible coatings. At the same time, arranged gold nanodots have important applications in electrochemical sensors. In this paper we perform a series of annealing experiments of gold and silver nanowires and nanowire junctions at fixed temperatures 473, 673, 873 and 973 K (200 °C, 400 °C, 600 °C and 700 °C) during a time period of 10 min. We show that nanowires are especially prone to fragmentation around junctions and crossing points even at comparatively low temperatures. The fragmentation process is highly temperature dependent and the junction region breaks up at a lower temperature than a single nanowire. We develop a gold parametrization for kinetic Monte Carlo simulations and demonstrate the surface diffusion origin of the nanowire junction fragmentation. We show that nanowire fragmentation starts at the junctions with high reliability and propose that aligning nanowires in a regular grid could be used as a technique for fabricating arrays of nanodots.

Size-Dictionary Interpolation for Robot's Adjustment.

This paper describes the classification and size-dictionary interpolation of the three-dimensional data obtained by a laser scanner to be used in a realistic virtual fitting room, where automatic activation of the chosen mannequin robot, while several mannequin robots of different genders and sizes are simultaneously connected to the same computer, is also considered to make it mimic the body shapes and sizes instantly. The classification process consists of two layers, dealing, respectively, with gender and size. The interpolation procedure tries to find out which set of the positions of the biologically inspired actuators for activation of the mannequin robots could lead to the closest possible resemblance of the shape of the body of the person having been scanned, through linearly mapping the distances between the subsequent size-templates and the corresponding position set of the bioengineered actuators, and subsequently, calculating the control measures that could maintain the same distance proportions, where minimizing the Euclidean distance between the size-dictionary template vectors and that of the desired body sizes determines the mathematical description. In this research work, the experimental results of the implementation of the proposed method on Fits.me's mannequin robots are visually illustrated, and explanation of the remaining steps toward completion of the whole realistic online fitting package is provided.

Ionic electroactive polymer artificial muscles in space applications.

A large-scale effort was carried out to test the performance of seven types of ionic electroactive polymer (IEAP) actuators in space-hazardous environmental factors in laboratory conditions. The results substantiate that the IEAP materials are tolerant to long-term freezing and vacuum environments as well as ionizing Gamma-, X-ray, and UV radiation at the levels corresponding to low Earth orbit (LEO) conditions. The main aim of this material behaviour investigation is to understand and predict device service time for prolonged exposure to space environment.

Nanothorn electrodes for ionic polymer-metal composite artificial muscles.

Ionic polymer-metal composites (IPMCs) have recently received tremendous interest as soft biomimetic actuators and sensors in various bioengineering and human affinity applications, such as artificial muscles and actuators, aquatic propulsors, robotic end-effectors, and active catheters. Main challenges in developing biomimetic actuators are the attainment of high strain and actuation force at low operating voltage. Here we first report a nanostructured electrode surface design for IPMC comprising platinum nanothorn assemblies with multiple sharp tips. The newly developed actuator with the nanostructured electrodes shows a new way to achieve highly enhanced electromechanical performance over existing flat-surfaced electrodes. We demonstrate that the formation and growth of the nanothorn assemblies at the electrode interface lead to a dramatic improvement (3- to 5-fold increase) in both actuation range and blocking force at low driving voltage (1-3 V). These advances are related to the highly capacitive properties of nanothorn assemblies, increasing significantly the charge transport during the actuation process.

Microporous and mesoporous carbide-derived carbons for strain modification of electromechanical actuators.

Low-voltage stimuli-responsive actuators based on carbide-derived carbon (CDC) porous structures were demonstrated. Bending actuators showed a differential electromechanical response defined by the porosity of the CDC used in the electrode layer. Highly porous CDCs prepared from TiC (mainly microporous), B4C (micromesoporous), and Mo2C (mainly mesoporous) precursors were selected to demonstrate the influence of porosity parameters on the electromechanical performance of actuators. CDC-based bending-type actuators showed a porosity-driven displacement response over a frequency range of 200 to 0.005 Hz at an applied excitation voltage of ±2 V. The displacement response of the CDC actuators increased with an increasing number of mesopores in the electrode layer, and the generated strain of the bending actuators was proportional to the total porosity (micropores and mesopores) of the CDC. The modifiable electromechanical response that arises from the precise porosity control attained through tailoring the CDC architecture demonstrates that these actuators hold great promise for smart, low-voltage-driven actuation devices.

Charging a supercapacitor-like laminate with ambient moisture: from a humidity sensor to an energy harvester.

The electromechanically and mechano-electrically active three-layered laminate composed of a Nafion membrane, carbide-derived carbon-based electrodes, and a 1-ethyl-3-methylimidazolium trifluoromethanesulphonate ionic liquid electrolyte responds to humidity gradient and can therefore serve as a differential humidity sensor or an energy harvesting element. The hydrophilic nature of all constituents of the laminate promotes sorption and diffusion of water across the membrane, causing large volumetric effects. Diffusion of water and the formation of a hydration shell around the ionic groups reorient and dislocate the ionic liquid ions, which in turn induce the formation of an electric charge across the electrodes exposed to different levels of ambient humidity. The generated electric charge can be registered as a voltage or electric current between the electrodes. Furthermore, the supercapacitor-like properties of the laminate allow storage of the electric charge in the same laminate, where it was generated.