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. These can simultaneously generate a movement (by applying an electric current/potential) and sense the effort of holding weights (by measuring the potential/current while holding objects up to 21.1 mg). Electroactivity was consisting in a fast bending/curling motion, depending on the fiber strip width. The amplitude of the movement decreases by increasing the load, a behavior similar with natural muscles. Moreover, when different weights were hung on the device, it senses the load modification, demonstrating a sensitivity of about 7 mV/mg for oxidation and - 4 mV/mg for reduction. These results are important since simultaneous actuation and sensitivity are essential for complex activity. Such devices with multiple functionalities can open new possibilities of applications as e.g. smart prosthesis or lifelike robots.

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: 1.4× higher strains, 1.3× higher specific charge densities, 2.5× higher specific capacitances and increased ion-sensitivity towards the studied counterions. For both materials, the reaction energy, the material potential and the strain variations adapt to and sense the electrical and chemical (exchanged cation) conditions. The driving and the response of actuation, sensing and charge can be controlled/read, simultaneously, via just two connecting wires. Only the cooperative actuation of chemical macromolecular motors from functional cells has such chemical multifunctionality.

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. The electro-chemo-mechanical characterization of the films was carried out by cyclic voltammetry and square wave potential steps in bis(trifluoromethane)sulfonimide lithium solutions of propylene carbonate (LiTFSI-PC). Linear actuation of the CFS-PPy/DBS material exhibited 20% of strain variation with a stress of 0.14 MPa, rather similar to skeletal muscles. After 1000 cycles, the creeping effect was as low as 0,2% having a good long-term stability showing a strain variation per cycle of -1.8% (after 1000 cycles). Those material properties are excellent for future technological applications as artificial muscles, batteries, smart membranes, and so on.

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. A complete characterisation of SF/rGO scaffolds is provided in terms of electrochemistry, mechanical behaviour and chemical conformation of fibroin. The excellent biocompatibility of this novel material is proved with cultures of PC-12 cells. The coating with rGO improved the adhesion of cells in comparison with cells growing onto the surface of pure SF scaffolds. Also, the use of SF/rGO scaffolds combined with electrical stimulation promoted the differentiation into neural phenotypes reaching comparable or even superior levels to those obtained by means of the traditional treatment with neural growth factor (NGF).

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. For more details, read the full text of the Full Paper at 10.1002/open.201600139.

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. Voltammetric, coulovoltammetric, and chronoamperometric responses from a LiClO4 aqueous solution indicated the formation of an energetically stable structure beyond a reduction threshold of the material. Its subsequent oxidation required higher anodic voltammetric overpotentials or longer chronoamperometric oxidation times. This structure was attributed to the formation of lamellar or vacuolar structures. X-ray photoelectron spectroscopy analysis of the films under different oxidations states revealed that the electrochemical reactions drive the reversible exchange of cations between the film and the electrolyte. The electrical energy and the charge consumed by the reversible reaction of the film under voltammetric conditions between the constant potential limits are a function of the potential scan rate, that is, they sense the working electrochemical conditions.

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. A maximum expansion was achieved in 0.3 M aqueous solution. The consumed oxidation and reduction charges control the fully reversible dimensional variations: PPy(DBS) films are faradaic polymeric motors. Parallel to the faradaic exchange of the cations, osmotic, electrophoretic, and structural changes play an important role for the water exchange and volume change of PPy(DBS).

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. The linearity indicates that cations are the only exchanged ions in the studied potential range. By flow of the same specific charge in every electrolyte, different angles were described by the muscle. The charge and the angle allow the number and volume of both the exchanged cations and the water molecules (related to a reference) between the film to be determined, in addition to the electrolyte per unit of charge during the driving reaction. The attained apparent solvation numbers for the exchanged cations were: 0.8, 0.7, 0.6, 0.5, 0.5, 0.4, 0.25, and 0.0 for Na(+), Mg(2+), La(3+), Li(+), Ca(2+), K(+), Rb(+), and Cs(+), respectively.

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 NaPF6. The Na, Cl, P, S and F content of films, after attaining a different oxidation state, were determined by EDX. The bending movements of the bilayer (PPy-HpPS)/tape artificial muscle were video recorded during potential sweeps in both solutions allowing the translation of the prevalent ionic exchanges driven by the biomimetic reactions into macroscopic movements. Ionic exchanges between the film and the solution, biomimetic structural processes in the film, driving prevalent electrochemical reactions and film compositions related to each of the different structural potential domains defined by coulovoltammetric results were clarified. In NaPF6 solutions a prevalent exchange of anions exists: the film swells by oxidation and shrinks by reduction. In NaCl solutions prevailing exchange of cations or anions occurs in different potential ranges. Reactions related to the HpPS content play important roles at the more cathodic and more anodic overpotentials. The described methodology could be translated to biological reactions including reactive biopolymers.

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. Being a general theoretical description, any reactive device based on the electrochemistry of conducting polymers or carbon based reactive compounds is expected to sense working and environmental conditions being described by those equations as tactile artificial muscles do. Only two connecting wires contain actuating (current) and sensing (potential) signals that are detected, simultaneously and at any actuating time, by the computer as mammalians brains do.

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...) variables. The current quantifies the actuation of any electrochemical device (charge/discharge of batteries, movement rate, and position of muscles): the stair functions are dual actuating-sensing functions. A good agreement exists between theoretical and experimental results from either polypyrrole films or artificial muscles at different temperatures. Only two connecting wires include, at any time, sensing (potential) and working (current) information of any dual device.

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. Furthermore, coated meshes present a high electroactivity allowing anion storage and delivery during oxidation/reduction reactions in aqueous solutions. Uncoated and pPy coated materials support the adherence and proliferation of adult human mesenchymal stem cells (ahMSCs) or human fibroblasts (hFb). The bioactivity of fibroin mesh overcomes that of the polypyrrole coated meshes.

Chronoamperometric study of conformational relaxation in PPy(DBS).

In conjugated polymer devices that switch from one oxidation level to another, such as artificial muscles, it is important to understand memory effects that stem from conformational relaxation movements of the polymer chains. Chronoamperometry during electrochemical switching of polypyrrole doped with dodecylbenzenesulfonate, PPy(DBS), is used to gain insight into the conformational relaxation processes in cation-transporting materials. During oxidation, the current decays exponentially with a time constant that decreases with the anodic voltage. During reduction, there is again an exponentially decaying current with a time constant that decreases with the cathodic voltage, but superimposed on that is a small current peak that increases in size with the voltage. This peak accounts for a maximum of approximately 20% of the total reduction charge, which is approximately the same amount of charge that is in the most cathodic pair of peaks in the cyclic voltammogram. The position of this peak depends logarithmically on the applied cathodic potential (shifting to shorter times with larger Eca) as well as on the anodic potential that was applied just prior to the reduction step (shifting to longer times with Ean). Furthermore, the shoulder position depends logarithmically on the time that the prior anodic voltage was held (shifting to longer times with twait). These results are consistent with the electrochemically stimulated conformational relaxation (ESCR) model.

Heterocyclic amines in griddled beef steak analysed using a single extract clean-up procedure.

Heterocyclic amines (HAs), which are potent mutagenic and carcinogenic substances, are formed in muscle meats during their cooking under ordinary conditions. In this work, we measured the concentration of 15 HAs in different samples of griddled beef steak, which is one of the most consumed meat items is Spain. Three samples were obtained from different restaurants, and the other sample was cooked under controlled conditions to a well-done degree of doneness. A low-time consuming solid-phase extraction procedure was used to purify the samples, and liquid chromatography-tandem mass spectrometry with an ion trap mass analyzer was used as determination technique. A second well-established purification procedure was used to demonstrate the applicability of the method to the analysis of these kind of samples. 8-MeIQx, 4,8-DiMeIQx, PhIP and the comutagens Harman and Norharman were found in all the samples, at levels ranging from 0.28 to 21.2ngg(-1). AalphaC was found in three samples (0.18-1.41ngg(-1)), whereas Trp-P-1 was detected in two samples (0.35ngg(-1)). MeAalphaC was found in three samples but could only be quantified in one (0.15ngg(-1)). Trp-P-2 and DMIP were also detected in some cases at levels below their limit of quantification. The remaining HAs analyzed were not detected in any of the samples.

In situ FTIR spectroscopy study of the break-in phenomenon observed for PPy/PVS films in acetonitrile.

The in situ Fourier transform infrared (in situ FTIR) technique was used for the first time to investigate the break-in phenomenon observed for polypyrrole/poly(vinyl sulfonate) (PPy/PVS) films in acetonitrile containing 0.1 M LiClO(4). Consecutive potential scans provided a continuous increase of the infrared band intensities, simultaneous to an increase observed in the charge involved in the voltammetric peaks, suggesting a rise in the number of the polymeric chains participating in the infrared signal at the same time as the electroactive participants increase in the redox process. Moreover, in situ FTIR spectra evidence that the new infrared-activated chains in each voltammetric cycle adopt the same polymeric structure achieved by the chains activated in the initial cycles. However, if we achieve a cathodic potential limit of -2.1 V (vs Ag/AgCl), a restructuring of the polymeric morphology is observed. In situ FTIR spectra obtained for PPy/ClO(4) films under the same conditions pointed to a steady-state behavior from the very early voltammetric scans. Moreover, the intensities of FTIR bands obtained for PPy/ClO(4) films in the early voltammetric cycles are much higher than those obtained for PPy/PVS films after several potential scans. Only when high cathodic and high anodic potential limits were used for the consecutive cycles did the FTIR band intensities from PPy/PVS become similar to those obtained from PPy/ClO(4), indicating that in both films a similar number of polymeric chains were infrared active. Polarization at a high anodic potential (+1.3 V vs Ag/AgCl) produced overoxidation of the polymer appearing characteristic 1725 cm(-1) band assigned to the formation of carbonyl groups. Furthermore, the approximately 1540 cm(-1) band shifted to higher wavenumbers, indicating that overoxidation reduced the length of conjugated chains in the polypyrrole.

Diffusion coefficients in swelling polypyrrole: ESCR and Cottrell models.

Reliable diffusion coefficients, D, for the diffusion of perchlorate anions into polypyrrole films during polymeric oxidation were obtained from chronoamperometric results. Two different models were used to calculate D: the Cottrell equation and the electrochemically stimulated conformational relaxation (ESCR) model. As expected, the initial Cottrell hypothesis was far from swelling/shrinking polymeric electrodes and the obtained D range was from 10(-10) to 10(-6) cm(2) s(-1). The ESCR model, based on the internal diffusion that takes place from regions where the steady state of oxidation has already been reached to regions where the oxidation is only just beginning, provided values of D ranging from 0.4 x 10(-9) to 2.2 x 10(-9) cm(2) s(-1), which is close to the values expected for a gel. When a constant amplitude is kept for the potential step, D increases with increasing initial anodic potentials, i.e., from increasingly swollen films. When it is stepped to the same oxidation potential, D decreases when starting from more cathodic potentials, i.e., from a more compact structure. These changes in D can be attributed to (i) swelling processes during oxidation, giving a gel-like structure; (ii) compacting processes at increasing cathodic potentials; (iii) the increasing thickness of the film during oxidation; and (iv) a decrease in film viscosity during the swelling process.

Comparison of different commercial solid-phase extraction cartridges used to extract heterocyclic amines from a lyophilised meat extract.

Heterocyclic amines are a group of potent mutagenic compounds which are generated when muscle meat is cooked. Since they are possible human carcinogens, these mutagens have received considerable attention in recent years, and several analytical techniques have been developed for their quantification. Although the purification step is one of the most important, there are a great number of variables influencing the recovery of the amines, especially when real samples are analysed. In this work we studied the influence of sample spiking mode on the recoveries. Furthermore, on the basis of a previously developed clean-up method, the effect of changing commercial source and structure of the sorbents used in two solid-phase extraction steps was examined. This purification method was applied to the quantification of the heterocyclic aromatic amines present in a lyophilised meat extract by means of liquid chromatography-mass spectrometry.

Evaluation of different clean-up procedures for the analysis of heterocyclic aromatic amines in a lyophilized meat extract.

Along with other mutagenic and carcinogenic contaminants in foods such as aflatoxins, and polycyclic aromatic hydrocarbons, heterocyclic aromatic amines (HAAs) have received considerable attention in recent years. A major drawback in the analysis of HAAs in foods is their very low level of concentration (0.1 50 ng g-1) as well as matrix interferences. Solid-phase extraction (SPE), forming an integral part of chromatographic analysis, is one of the procedures currently used for the extraction and purification of HAAs in food samples. In this paper a comparative study of several SPE procedures for HAAs determination was performed. Recoveries of the heterocyclic amines in the analysis of both a simple matrix such as a standard methanolic solution and a contaminated meat extract were established. HAAs were determined by HPLC analysis with photodiode-array detection (DAD) of the purified extracts, and the adequacy of different clean-up procedures for the analysis of a contaminated meat extract was discussed.

The levels of ribonucleotide reductase, thioredoxin, glutaredoxin 1, and GSH are balanced in Escherichia coli K12.

The dithiol forms of thioredoxin and glutaredoxin are hydrogen donors for ribonucleotide reductase. We have determined the intracellular levels of ribonucleotide reductase (RRase), thioredoxin (Trx), glutaredoxin 1 (Grx1), and glutathione (GSH) and the glutathione redox status in new Escherichia coli K12 strains lacking thioredoxin (trxA-), glutaredoxin 1 (grxA-), and/or GSH (gshA-) or overproducing Trx or Grx1 from multicopy plasmids. We propose a regulatory network in which RRase levels are balanced with those of Trx, Grx1, and GSH so that deficiency or overproduction of one component would promote the opposite effect on the others to maintain a balanced supply of deoxyribonucleotides. GSH deficiency strongly increased both Grx1 levels and RRase activity, even more than Trx deficiency. Double gshA-trxA- bacteria were viable, whereas additional deficiency in lipoate synthesis (gshA-trxA-lipA-) caused the inability to grow in minimal medium plates supplemented with acetate plus succinate instead of lipoic acid. Thus, lipoate might be the only substitute of GSH for glutaredoxin reduction in gshA-trxA- cells, although the extremely high Grx1 content (55-fold) of these bacteria suggests that electron transfer from lipoate might be an inefficient reduction mechanism of glutaredoxins. Moreover, the enhanced Grx1 level of gshA-trxA- cells could obviate the need for a large increase in RRase activity, in contrast to grxA-trxA- double mutant cells. Impairment of the sulfate assimilation pathway, leading to very low GSH concentrations, and an oxidized glutathione redox state might explain the inability of grxA-trxA- cells to grow in minimal medium. Restoration of nearly normal levels of both GSH content and redox status cure the growth defect.