Bioinspired polypyrrole based fibrillary artificial muscle with actuation and intrinsic sensing capabilities.

A non-conventional, bioinspired device based on polypyrrole coated electrospun fibrous microstructures, which simultaneously works as artificial muscle and mechanical sensor is reported. Fibrous morphology is preferred due to its high active surface which can improve the actuation/sensing properties, its preparation still being challenging. Thus, a simple fabrication algorithm based on electrospinning, sputtering deposition and electrochemical polymerization produced electroactive aligned ribbon meshes with analogous characteristics as natural muscle fibers.

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.

Enhancing the electrocatalytic activity and stability of Prussian blue analogues by increasing their electroactive sites through the introduction of Au nanoparticles.

Prussian blue analogues (PBAs) have been proven as excellent Earth-abundant electrocatalysts for the oxygen evolution reaction (OER) in acidic, neutral and alkaline media. Further improvements can be achieved by increasing their electrical conductivity, but scarce attention has been paid to quantify the electroactive sites of the electrocatalyst when this enhancement occurs. In this work, we have studied how the chemical design influences the specific density of electroactive sites in different Au-PBA nanostructures.

Multifunctionality of Polypyrrole Polyethyleneoxide Composites: Concurrent Sensing, Actuation and Energy Storage.

In films of conducting polymers, the electrochemical reaction(s) drive the simultaneous variation of different material properties (reaction multifunctionality). Here, we present a parallel study of actuation-sensing-energy storage triple functionality of polypyrrole (PPy) blends with dodecylbenzenesulfonate (DBS-), PPy/DBS, without and with inclusion of polyethyleneoxide, PPy-PEO/DBS. The characterization of the response of both materials in aqueous solutions of four different salts indicated that all of the actuating, sensing and charge storage responses were, independent of the electrolyte, present for both materials, but stronger for the PPy-PEO/DBS films: 1.

Concept of an artificial muscle design on polypyrrole nanofiber scaffolds.

Here we present the synthesis and characterization of two new conducting materials having a high electro-chemo-mechanical activity for possible applications as artificial muscles or soft smart actuators in biomimetic structures. Glucose-gelatin nanofiber scaffolds (CFS) were coated with polypyrrole (PPy) first by chemical polymerization followed by electrochemical polymerization doped with dodecylbenzensulfonate (DBS-) forming CFS-PPy/DBS films, or with trifluoromethanesulfonate (CF3SO3-, TF) giving CFS-PPy/TF films. The composition, electronic and ionic conductivity of the materials were determined using different techniques.

A COTS-Based Portable System to Conduct Accurate Substance Concentration Measurements.

Traditionally, electrochemical procedures aimed at determining substance concentrations have required a costly and cumbersome laboratory environment. Specialized equipment and personnel obtain precise results under complex and time-consuming settings. Innovative electrochemical-based sensors are emerging to alleviate this difficulty.

Structural and Conformational Chemistry from Electrochemical Molecular Machines. Replicating Biological Functions. A Review.

Each constitutive chain of a conducting polymer electrode acts as a reversible multi-step electrochemical molecular motor: reversible reactions drive reversible conformational movements of the chain. The reaction-driven cooperative actuation of those molecular machines generates, or destroys, inside the film the free volume required to lodge/expel balancing counterions and solvent: reactions drive reversible film volume variations, which basic structural components are here identified and quantified from electrochemical responses. The content of the reactive dense gel (chemical molecular machines, ions and water) mimics that of the intracellular matrix in living functional cells.

Electrospun silk fibroin scaffolds coated with reduced graphene promote neurite outgrowth of PC-12 cells under electrical stimulation.

Novel approaches to neural research require biocompatible materials capable to act as electrode structures or scaffolds for tissue engineering in order to stimulate or restore the functionality of damaged tissues. This work offers promising results that indicate the potential use of electrospun silk fibroin (SF) scaffolds coated with reduced graphene oxide (rGO) in this sense. The coated material becomes conductor and electroactive.

Self-Supported Polypyrrole/Polyvinylsulfate Films: Electrochemical Synthesis, Characterization, and Sensing Properties of Their Redox Reactions.

Thick films of polypyrrole/polyvinylsulfate (PPy/PVS) blends were electrogenerated on stainless-steel electrodes under potentiostatic conditions from aqueous solution. The best electropolymerization potential window was determined by cyclic voltammetry. After removing the film from the back metal, self-supported electrodes were obtained.

Self-Supported Polypyrrole/Polyvinylsulfate Films: Electrochemical Synthesis, Characterization, and Sensing Properties of Their Redox Reactions.

Invited for this month's cover picture is the group of Professor Toribio F. Otero at the Centre for Electrochemistry, Intelligent Materials and Devices at the Polytechnic University of Cartagena (Spain). The cover picture shows an electrochemical cell as well as three representative cyclic voltammetric responses, displaying the electrolyte potential window, the monomer oxidation-polymerization potential range, and the polymer oxidation-reduction potential window.

Reactions driving conformational movements (molecular motors) in gels: conformational and structural chemical kinetics.

In this perspective the empirical kinetics of conducting polymers exchanging anions and solvent during electrochemical reactions to get dense reactive gels is reviewed. The reaction drives conformational movements of the chains (molecular motors), exchange of ions and solvent with the electrolyte and structural (relaxation, swelling, shrinking and compaction) gel changes. Reaction-driven structural changes are identified and quantified from electrochemical responses.

Fabrication of electrospun silk fibroin scaffolds coated with graphene oxide and reduced graphene for applications in biomedicine.

Silk fibroin and graphene are both promising biomaterials described in the bibliography. Hybrid scaffolds combining their properties could be attractive for tissue engineering applications. In this work, a new methodology to produce electrospun fibroin scaffolds coated with graphene materials is provided.

Deep Reduced PEDOT Films Support Electrochemical Applications: Biomimetic Color Front.

Most of the literature accepts, despite many controversial results, that during oxidation/reduction films of conducting polymers (CPs) move from electronic conductors to insulators. Thus, engineers and device's designers are forced to use metallic supports to reoxidize the material for reversible device work. Electrochromic front experiments appear as main visual support of the claimed insulating nature of reduced CPs.

Polypyrrole-para-phenolsulfonic acid/tape artificial muscle as a tool to clarify biomimetic driven reactions and ionic exchanges.

Thick films of the polypyrrole-para-phenolsulfonic acid (PPy-HpPS) blend were electrogenerated on stainless steel plates. The self-supported films, once peeled off from the metal, were electrochemically characterized in aqueous solutions of NaCl and NaPF. The Na, Cl, P, S and F content of films, after attaining a different oxidation state, were determined by EDX.

Effect of the electrolyte concentration and substrate on conducting polymer actuators.

The effect of the electrolyte concentration (NaCl aqueous electrolyte) on the dimensional variations of films of polypyrrole doped with dodecylbenzenesulfonate PPy(DBS) on Pt and Au wires was studied. Any parallel reaction that occurs during the redox polymeric reaction that drives the mechanical actuation, as detected from the coulovoltammetric responses, was avoided by using Pt wires as substrate and controlling the potential limits, thus significantly increasing the actuator lifetime. The NaCl concentration of the electrolyte, when studied by cyclic voltammetry or chronoamperometry, has a strong effect on the performance as well.

Exchanged cations and water during reactions in polypyrrole macroions from artificial muscles.

The movement of the bilayer (polypyrrole-dodecylbenzenesulfonate/tape) during artificial muscle bending under flow of current square waves was studied in aqueous solutions of chloride salts. During current flow, polypyrrole redox reactions result in variations in the volumes of the films and macroscopic bending: swelling by reduction with expulsion of cations and shrinking by oxidation with the insertion of cations. The described angles follow a linear function, different in each of the studied salts, of the consumed charge: they are faradaic polymeric muscles.

Reactions drive conformations. Biomimetic properties and devices, theoretical description.

Life is supported by cellular reactions driving conformational, folding and unfolding macromolecular movements with ionic and aqueous exchange. Here we review the state of the art of the electrochemistry of conducting polymers as elemental material models of biological reactive gels. The different experimental methodologies allowing identification and quantification of the reaction induced molecular (conformation) and macroscopic (relaxation, swelling, shrinking and compaction) structural changes are reviewed.

Biomimetic intracellular matrix (ICM) materials, properties and functions. Full integration of actuators and sensors.

The electrochemistry of conducting polymers, and other organic compounds, originates biomimetic (intracellular matrix, ICM, reactive gels) materials, properties and devices here reviewed. One reaction changes several properties (multifunctionality): one device can integrate different actuators (artificial muscles, batteries, smart windows) and sensors (temperature, concentration, mechanical). Actuating (current and charge) and sensing (potential) magnitudes are present in the two connecting wires, and can be read by the computer, at any working time mimicking brain-organs dialog.

Biomimetic dual sensing-actuators: theoretical description. Sensing electrolyte concentration and driving current.

Here we present the theoretical (electrochemical and polymeric) description of chronopotentiometric responses (under driven constant current) from reacting conducting polymers both, as films or taking part of electrochemical devices, that sense driving current and electrolyte concentration during reactive actuation. The attained sensing-actuation equations describe the potential, or the consumed electrical energy, evolution as a function of working and environmental variables: driving current, temperature, electrolyte concentration, or mechanical conditions. Good agreement between theoretical and experimental results is attained here by using polypyrrole films under flow of different currents or in different electrolyte concentrations.

Biomimetic dual sensing-actuators based on conducting polymers. Galvanostatic theoretical model for actuators sensing temperature.

A theoretical model is proposed for the quantitative description of the chronopotentiometric (E-t) responses, under galvanostatic control, of either conducting polymer films or dual sensing-actuating devices. Assuming that the reaction occurs by extraction, or injection, of n consecutive electrons from, or to, a polymer chain the material moves through n consecutive oxidation or reduction states. Stair functions are obtained describing either potential or consumed electrical energy evolutions as a function of both, driving (current) and environmental (temperature, electrolyte concentration.

Electrochemistry of carbon nanotubes: reactive processes, dual sensing-actuating properties and devices.

Single-walled carbon nanotubes (SWCNT) embedded in a non-electroactive polymer are electrochemically characterized. The increasing voltammetric maximums obtained with rising temperature or electrolyte concentration point to a chemical nature of the processes. The chemical kinetic control of the processes is corroborated by its empirical chemical kinetics: the initial reaction rates are obtained from the chronoamperometric responses to potential steps.

Fabrication of conductive electrospun silk fibroin scaffolds by coating with polypyrrole for biomedical applications.

Scaffolds constituted by micro and nanofibers of silk fibroin were obtained by electrospinning. Fibers of fibroin meshes were coated with polypyrrole (pPy) by chemical polymerization; chemical linkages between polymers were observed by SEM and IR spectroscopy. Mechanical resistance of the meshes was improved by polypyrrole coating.

Electropolymerization of naphthaleneamidinemonoimide-modified poly(thiophene).

The new polymer presents a p-doping process with anion exchange and its electrochemical reduction with cation exchange during potential cycling. Stored specific charges of 38 mAh g(-1) for the polymer reduction and 13 mAh g(-1) for its oxidation make the material very promising for fast charge/discharge batteries or specialised supercapacitors in which the material is also required as the anode.

High-speed carbon nanotube actuators based on an oxidation/reduction reaction.

Actuators with a high-speed response under a high-frequency (more than 100 Hz) applied square-wave voltage of ±2 V have been developed with an electrode composed of millimeter-long single-walled carbon nanotubes synthesized by the "supergrowth method" (SG-SWNTs) and ionic liquids (ILs). Detailed studies concerning induced electric current and transferred charge in the electrode as well as cyclic voltammetric studies of the electrode revealed that the high-speed response originates from the electric current generated by an oxidation/reduction (redox) reaction in addition to electric double-layer charging. The contribution of the redox reactions of SG-SWNTs to the actuation is sensitive to the presence of supporting polymers, the thickness of the electrolyte, and the amplitude of the applied voltage.

Sensing and tactile artificial muscles from reactive materials.

Films of conducting polymers can be oxidized and reduced in a reversible way. Any intermediate oxidation state determines an electrochemical equilibrium. Chemical or physical variables acting on the film may modify the equilibrium potential, so that the film acts as a sensor of the variable.