Dr. Mihaela BEREGOI

Amyloid beta (A(3) peptide aggregates are well-established biomarkers for Alzheimer's disease, though the complete etiology of this disorder remains elusive. Developing biointerfaces to elucidate the physiological roles of these peptides is essential. This study investigates the aggregation, fibrillation, and interaction of A(3 peptides with conductive, biocompatible nanostructured materials designed for applications involving neuronal cells. Various conductive, rigid, and flexible surfaces, both functionalized and non-functionalized with A(340 fibrils, were fabricated. These included glass substrates and poly(methyl methacrylate) electrospun fiber networks coated with gold via magnetron sputtering. The substrates were also functionalized through physical adsorption with poly-L-lysine and collagen, known to support cell proliferation, as well as with the inverse-A(340 peptide and an Amyloid Protein Non-A(3 Component, and the results were compared. The scaffolds were characterized using scanning electron microscopy, X-ray diffraction, atomic force microscopy, contact angle and electrical measurements, while their biological interactions were assessed using MTS assays, fluorescence imaging, and scanning electron microscopy. Fibroblast L929 and neuroblastoma SH-SY5Y cell lines were used as models, with results indicating an elevated cell viability, comparable to the control. The developed nanostructured surfaces are highly promising for integration into advanced neuromorphic engineering devices, as they have proven capable of maintaining their structural integrity when exposed to proteases.

The rapid growth of the global population has increased the need for efficient fabrication methods and materials to purify polluted water. In this study, we report the fabrication and characterization of reusable and efficient three-dimensional (3D) polydimethylsiloxane (PDMS) sponge composites designed for water treatment applications. By varying the ratios (10/90, 30/70, and 50/50) of large and small sacrificial templates' particles used in the fabrication method, we tailored the sponge's morphology and the interconnected pores' distribution. To achieve an enhanced photocatalytic activity, we incorporated titanium dioxide (TiO2) at different concentrations (1 % TiO2, 5 % TiO2, and 10 % TiO2 w/w) into the PDMS matrix. Scanning electron microscopy (SEM) was used to evaluate the structure of both 3D PDMS and TiO2@PDMS sponges, while energy dispersive X-ray analysis (EDX) and X-ray diffraction (XRD) confirmed the successful incorporation of TiO2 into the sponge framework. The photocatalytic performance of the 3D TiO2@PDMS composites was assessed by monitoring the degradation of Rhodamine B (RhB) under solar light irradiation, and the results were compared to those obtained using reference (TiO2-free) sponges under identical conditions. Very low Ti leaching effect have been evidenced by using Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). The reusability of the sponges was demonstrated through complete bleaching of the 554 nm RhB absorption band after four consecutive degradation cycles.

Paper-based devices hold great promise in biosensing, but the choice of electrode materials influences performance. Here, we report a paper-based electrochemical sensor developed for nucleic acid quantification, in a sandwich-type architecture integrating 3-electrode systems on metallized electrospun polymeric fibers. A 3D-printed hydrophobic barrier on the chromatographic paper defines injection and testing zones. Fluid diffusion through paper and concentration gradients are considered in the design. Electrochemical characterization is performed using 40 mu L of methylene blue solution, which interacts with double-stranded nucleic acids, reducing its redox activity. This interaction mechanism within the paper substrate is confirmed by spectroscopy. The sensor achieves detection of nucleic acids in 3 min with 2 mu L of solution. Real sample analysis is performed for the quantification of PCR-amplified genes with a limit of detection of 1.38 ng mu L-1. The device serves as a promising point-of-care diagnostics tool for the direct quantification of amplified genetic material.

The present study aims to develop and investigate the biological response of a bone substitute based on electrospun polyvinylidene fluoride (PVDF) fibres, which are either embedded or coated with a silicate bioglass belonging to SiO2-P2O5-CaO-Na2O oxide system. This bioglass is substituted with antibacterial agents, silver (Ag) and cerium (Ce), while deposition methods utilized include pulsed laser deposition (PLD) and matrixassisted pulsed laser evaporation (MAPLE). The results showed the inhomogeneous distribution of the glassy particulate phase in the polymer fibres when using electrospinning as single processing technique. In contrast, the materials achieved by combining the electrospinning with laser ablation displayed a continuous coating of glass at the polymer fibres surface. The thickness and roughness of this layer can be easily tuned as a function of deposition conditions, as it was demonstrated when changing the dispersion medium or working pressure. Good results were obtained for all coated PVDF fibres, but especially in the case of PLD processing with a thicker layer of silicate glass, the imaging evaluation suggested a superior beneficial impact on cellular metabolism. Such scaffolds, with controlled porosity, engineered surface and potential piezoelectric properties represent important candidates for the field of personalized bone substitutes.

A novel scaffold for in situ electrochemical detection of cell biomarkers was developed using electrospun nanofibers and commercial adhesive polymeric membranes. The electrochemical sensing of cell biomarkers requires the cultivation of the cells on/near the (bio)sensor surface in a manner to preserve an appropriate electroactive available surface and to avoid the surface passivation and sensor damage. This can be achieved by employing biocompatible nanofiber meshes that allow the cells to have a normal behavior and do not alter the electrochemical detection. For a better mechanical stability and ease of handling, nylon 6/6 nanofibers were collected on commercial polymeric membranes, at an optimal fiber density, obtaining a double-layered platform. To demonstrate the functionality of the fabricated scaffold, the screening of cellular stress has been achieved integrating melanoma B16-F10 cells and the (bio)sensor components on the transducer whereas the melanin exocytosis was successfully quantified using a commercial electrode. Either directly on the surface of the (bio)sensor or spatially detached from it, the integration of cell cultures in biosensing platforms based on electrospun nanofibers represents a powerful bioanalytical tool able to provide real-time information about the biomarker release, enzyme activity or inhibition, and monitoring of various cellular events.

Electrospun nanofibres based on poly(styrene sulfonate) doped poly(3,4-ethylenedioxythiophene) (PEDOT:PSS) were fabricated using a straightforward procedure which combines electrospinning, sputtering deposition and electrochemical synthesis. In general, electrospun fibre meshes based on conducting polymers are prepared by mixing the conducting polymer with a carrier polymer or chemically coverage of the fibres. In contrast, freestanding nylon 6/6 nanofibre webs were prepared through electrospinning and were coated by sputtering with gold in order to make them conductive. Further, a PEDOT:PSS layer was electrochemically deposited onto the metalized nanofibre meshes and the synthesis parameters were chosen in such a way to preserve the high active area of the fibres. The prepared material was morphologically characterized and the formation of PEDOT:PSS was also demonstrated. The PEDOT:PSS coated nanofibres revealed remarkable electrical properties (sheet resistance of about 3.5 Omega cm(-2)), similar to those of metalized nanofibres (sheet resistance around 3 Omega cm2). The in vitro studies using L929 fibroblast mouse cells showed that the bioactive material has no cytotoxic effect and allows proliferation. Moreover, after 72 h of incubation, the fibroblasts shrunk their nuclei and spread suggesting that a differentiation in myofibroblast occurs without application of any kind of external stimuli. These results will be helpful for developing efficient materials for wound healing applications that work without energy consumption.

In this work, polyvinylidene fluoride (PVDF) fibres loaded with mineral powders, such as titanium dioxide (TiO2), barium titanate (BaTiO3), and calcium magnesium silicate (CaxMgSi2Oy), were prepared by electrospinning polymeric suspensions containing 20 wt.% PVDF and 3 wt.% powder. The piezoelectric polymer was combined with powders having antibacterial, piezoelectric, or bioactive properties, respectively, in the desire to obtain multifunctional materials compatible with the requirements of the medical field. All powders were characterized in terms of morphology and crystalline structure, which confirmed the nanometric character of TiO2 samples and micrometric one for the other two, as well as the lower crystallite size for TiO2 specimens as against BaTiO3 and CaxMgSi2Oy. The final fibrous scaffolds were homogeneous, composed of individual fibres with a diameter below 1 mu m and decorated with aggregates of inorganic particles, placed either inside the fibres or attached to their surface. The biological evaluation demonstrated the superiority of the composites towards the plain polymer in terms of cell viability.

In this work, polyvinylidene fluoride was obtained in the form of one-dimensional structures with the help of electrospinning technique. Several types of precursor solutions were tested to find the optimal experimental conditions to produce smooth, continuous and beadless fibres, morphologically suitable for the development of piezoelectric scaffolds dedicated to tissue engineering applications. Thus, the influence of solvent type, polymer concentration, as well as electrospinning parameters (feeding rate, spinneret-collector distance, and applied voltage) was assessed and the best situation was the one with a 2:3 ratio between dimethylformamide and acetone, 20 % polymer concentration, 1 mL/h flow, 20 cm distance and 18 kV voltage. In the end, the fibres were loaded with barium titanate commercial particles, as first attempt to produce a piezoelectric composite with potential in the medical field.

The present work reports a new configuration of soft artificial muscle based on a web of metal covered nylon 6/6 micrometric fibers attached to a thin polydimethylsiloxane (PDMS) film. The preparation process is simple and implies the attachment of metalized fiber networks to a PDMS sheet substrate while heating and applying compression. The resulting composite is versatile and can be cut in different shapes as a function of the application sought. When an electric current passes through the metallic web, heat is produced, leading to local dilatation and to subsequent controlled deformation. Because of this, the artificial muscle displays a fast and ample movement (maximum displacement of 0.8 cm) when applying a relatively low voltage (2.2 V), a consequence of the contrast between the thermal expanse coefficients of the PDMS substrate and of the web-like electrode. It was shown that the electrical current producing this effect can originate from both direct electric contacts, and untethered configurations i.e. radio frequency induced. Usually, for thermal activated actuators the heating is produced by using metallic films or conductive carbon-based materials, while here a fast heating/cooling process is obtained by using microfiber-based heaters. This new approach for untethered devices is an interesting path to follow, opening a wide range of applications were autonomous actuation and remote transfer of energy are needed.

Electrospun polymeric fibers present an emerging alternative for the development of flexible electronics, enabling applications in wearable sensors and biosensors for continuous monitoring, and actuators for tissue engineering. The possibility to prepare sub-micrometric polymeric scaffolds, their processing for increasing the conductivity, their modification with different materials, conductive polymers and biomolecules in order to obtain functional flexible electrodes, allows the development of innovative devices for healthcare, and biomedical applications. In this review, the impact of metallized electrospun polymeric fibers in electrochemical (bio)sensors and actuators is discussed. A relation between their structure and functionality is provided, alongside with an overview of the different methods to obtain functional conductive fibers.

The present work reports the synthesis and characterization of polycaprolactone fibers loaded with particulate calcium magnesium silicates, to form composite materials with bioresorbable and bioactive properties. The inorganic powders were achieved through a sol-gel method, starting from the compositions of diopside, akermanite, and merwinite, three mineral phases with suitable features for the field of hard tissue engineering. The fibrous composites were fabricated by electrospinning polymeric solutions with a content of 16% polycaprolactone and 5 or 10% inorganic powder. The physico-chemical evaluation from compositional and morphological points of view was followed by the biological assessment of powder bioactivity and scaffold biocompatibility. SEM investigation highlighted a significant reduction in fiber diameter, from around 3 mu m to less than 100 nm after the loading stage, while EDX and FTIR spectra confirmed the existence of embedded mineral entities. The silicate phases were found be highly bioactive after 4 weeks of immersion in SBF, enriching the potential of the polymeric host that provides only biocompatibility and bioresorbability. Moreover, the cellular tests indicated a slight decrease in cell viability over the short-term, a compromise that can be accepted if the overall benefits of such multifunctional composites are considered.

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.

Embedding electronic and optoelectronic devices in common, daily use objects is a fast developing field of research. New architectures are needed for migrating from the classic wafer- based substrates. Novel types of flexible PMMA/Au/Alq(3)/LiF/Al structures were obtained starting from electrospun polymer fibers. Thus, using an electrospinning process poly (methyl metacrylate) (PMMA) nanofibers were fabricated. A thin Au layer deposition rendered the fiber array conductive, this being further employed as the anode. The next steps consisted of the thermal evaporation of tris(8-hydroxyquinolinato) aluminum (Alq(3)) and aluminum deposition as the cathode. The Au covered PMMA nanofiber layer had a similar behavior with an indium tin oxide film i.e. low sheet resistance 10.6 omega/sq and high transparency. The low electrode resistivities allow an electron drift mobility of about 10(-6) cm(2) V-1 s(-1) at a low applied field, similar to the counterpart structures based on thin films. Concerning the relaxation processes in these structures, the Cole-Cole plots exhibit a slightly deformed semicircle, indicating a more complex equivalent circuit for the processes between metal electrodes and the active layer. This equivalent circuit includes reactance equivalent processes at the anode, cathode, in the active layer and most probably originates from the roughness of the metallic electrodes.

Designing complex electrochemical artificial muscles aims towards novel devices which besides excellent actuation capabilities should also present the ability to self-sense the modification of environmental parameters. In order to improve efficiency, mimicking the structure of natural muscles, synthetic actuators should have a similar fibrillary morphology. The importance of using materials based on fiber building blocks in actuators aimed at soft robotics field was demonstrated in the present report by comparing a fibrillary artificial muscle with one based on a classical film structure. Nylon electrospun fiber meshes and films were covered in the same conditions with a thin polypyrrole (PPy) layer. The fibrillary electrospun web morphology mimics that of natural muscles and the structure performs a fast, ample bending movement in liquid electrolyte when switching an applied electric potential between -0.6 and +0.6 V. Using the same actuation conditions, no movement of a film based artificial muscle was observed. In order to check the sensing ability of both fibrillary and film like electroactive architectures, their response i.e. PPy reaction when potential cycles were applied in different concentrations of LiClO4 electrolyte were recorded. The obtained results suggest that the ion exchange of the fibrillary artificial muscle is more efficient due to its higher active surface and such devices could work also as dual device (sensor/artificial muscle).

Biopolymers provide versatile platforms for designing naturally-derived wound care dressings through eco-friendly pathways. Eggshell membrane (ESM), a widely available, biocompatible biopolymer based structure features a unique 3D porous interwoven fibrous protein network. The ESM was functionalized with inorganic compounds (Ag, ZnO, CuO used either separately or combined) using a straightforward deposition technique namely radio frequency magnetron sputtering. The functionalized ESMs were characterized from morphological, structural, compositional, surface chemistry, optical, cytotoxicity and antibacterial point of view. It was emphasized that functionalization with a combination of metal oxides and exposure to visible light results in a highly efficient antibacterial activity against Escherichia coli when compared to the activity of individual metal oxide components. It is assumed that this is possible due to the fact that an axial p-n junction is created by joining the two metal oxides. This structure separates into components the charge carrier pairs promoted by visible light irradiation that further can influence the generation of reactive oxygen species which ultimately are responsible for the bactericide effect. This study proves that, by employing inexpensive and environmentally friendly materials (ESM and metal oxides) and fabrication techniques (radio frequency magnetron sputtering), affordable antibacterial materials can be developed for potential applications in chronic wound healing device area.

Core-double shell nylon-ZnO/polypyrrole electrospun nanofibers were fabricated by combining three straightforward methods (electrospinning, sol-gel synthesis and electrodeposition). The hybrid fibrous organic-inorganic nanocomposite was obtained starting from freestanding nylon 6/6 nanofibers obtained through electrospinning. Nylon meshes were functionalized with a very thin, continuous ZnO film by a sol-gel process and thermally treated in order to increase its crystallinity. Further, the ZnO coated networks were used as a working electrode for the electrochemical deposition of a very thin, homogenous polypyrrole layer. X-ray diffraction measurements were employed for characterizing the ZnO structures while spectroscopic techniques such as FTIR and Raman were employed for describing the polypyrrole layer. An elemental analysis was performed through X-ray microanalysis, confirming the expected double shell structure. A detailed micromorphological characterization through FESEM and TEM assays evidenced the deposition of both organic and inorganic layers. Highly transparent, flexible due to the presence of the polymer core and embedding a semiconducting heterojunction, such materials can be easily tailored and integrated in functional platforms with a wide range of applications.

Staggered gap radial heterojunctions based on ZnO-CuxO core-shell nanowires are used as water stable photocatalysts to harvest solar energy for pollutants removal. ZnO nanowires with a wurtzite crystalline structure and a band gap of approximately 3.3 eV are obtained by thermal oxidation in air. These are covered with an amorphous CuxO layer having a band gap of 1.74 eV and subsequently form core-shell heterojunctions. The electrical characterization of the ZnO pristine and ZnO-CuxO core-shell nanowires emphasizes the charge transfer phenomena at the junction and at the interface between the nanowires and water based solutions. The methylene blue degradation mechanism is discussed taking into consideration the dissolution of ZnO in water based solutions for ZnO nanowires and ZnO-CuxO core-shell nanowires with different shell thicknesses. An optimum thickness of the CuxO layer is used to obtain water stable photocatalysts, where the ZnO-CuxO radial heterojunction enhances the separation and transport of the photogenerated charge carriers when irradiating with UV-light, leading to swift pollutant degradation.

The work describes the development of a flexible, hydrogel embedded pH-sensor that can be integrated in inexpensive wearable and non-invasive devices at epidermal level for electrochemical quantification of H+ ions in sweat. Such a device can be useful for swift, real time diagnosis and for monitoring specific conditions. The sensors' working electrodes are flexible poly(methyl methacrylate) electrospun fibers coated with a thin gold layer and electrochemically functionalized with nanostructured palladium/palladium oxide. The response to H+ ions is investigated by cyclic voltammetry and electrochemical impedance spectroscopy while open circuit potential measurements show a sensitivity of aprox. -59 mV per pH unit. The modification of the sensing interface upon basic and acid treatment is characterized by scanning and transmission electron microscopy and the chemical composition by X-ray photoelectron spectroscopy. In order to demonstrate the functionality of the pH-sensor at epidermal level, as a wearable device, the palladium/palladium oxide working electrode and silver/silver chloride reference electrode are embedded within a pad of polyacrylamide hydrogel and measurements in artificial sweat over a broad pH range were performed. Sensitivity up to -28 mV/pH unit, response time below 30 s, temperature dependence of approx. 1 mV/degrees C as well as the minimum volume to which the sensor responses of 250 nanoliters were obtained for this device. The proposed configuration represents a viable alternative making use of low-cost and fast fabrication processes and materials.

Electrospun sub-micrometer polymer fiber mats represent an interesting substrate which can be employed as a transparent conducting electrode. Functionalization by using nanostructures represents a convenient way of increasing the range of applications. The present paper describes an electrodeposition process which can be applied for preparing ZnO nanostructures covered fibers in a straightforward manner. Poly(methyl methacrylate) fiber mats were obtained by electrospinning using metal frame collectors. Subsequent metallization by DC sputtering was used, these microstructured electrodes being thermally transferred onto glass substrates and further employed as working electrodes for the electrochemical deposition of ZnO. The transparency of the metal covered webs, a function of fiber density, is comparable to that of conventional transparent conductive oxides electrodes such as ITO. The same enhanced control of the ZnO electrodeposition process was observed for the case of the web electrodes as for the classic case of deposition on transparent conducting oxides or on metallic substrates. Structural, optical, morphological and wetting properties were investigated and correlated with the electrodeposition conditions. The photocatalytic properties of ZnO covered fibers were tested through the decomposition of methylene blue thin films under UV irradiation.

This paper proposes a novel, flexible, low cost administration patch which could be used as a non-invasive, controlled transdermal drug delivery system. The fabricated device consists in a flexible microfiber architecture heater covered with a thermoresponsive hydrogel, namely poly(N-isopropylacrylamide), as a matrix for the incorporation of active molecules. The manufacturing process consists of two main steps. First, the electrospun poly(methyl methacrylate) fiber networks are sputter coated with a thin gold layer and attached to flexible poly(ethylene terephthalate) substrates to obtain the heating platforms. Second, the heaters are encapsulated in poly(ethylene terephthalate) foils and covered with poly(N-isopropylacrylamide) hydrogel sheets. In order to illustrate the functionality of the fabricated patch, the hydrogel layer is loaded with methylene blue aqueous solution and is afterwards heated via Joule effect, by applying a voltage on the metalized fibers. The methylene blue releasing profiles of the heated patch are compared with those of the unheated one and the influence of parameters such as hydrogel composition and morphology, as well as the applied voltage values for microheating are investigated. The results indicate that the fabricated patch can be used as a drug administration instrument, while its performance can be tuned depending on the targeted application.

Ceramic thin films belonging to SiO2-P2O5-CaO-MgO-ZnO-CaF2 system were obtained by combining the sol-gel approach with the spin coating technique. Titanium plates were employed as substrates. The deposited coatings were characterized in terms of composition, structure and morphology with the help of the following methods: X-ray diffraction, Fourier - transform infrared spectroscopy and scanning electron microscopy coupled with energy - dispersive X-ray spectroscopy. In order to assess the bioactivity of a potential metallic implant covered with such layers, the samples were immersed in simulated body fluid for 14 days and their surface was investigated. The results showed that the thin films calcined at a lower temperature have a better biological response due to the vitroceramic nature.

Eggshell membranes were employed as biological scaffolds for developing soft and versatile actuators. A particular architecture, consisting of eggshell membrane coated with polypyrrole, has been fabricated and has been found to be a green, inexpensive, lightweight, and easy to handle class of actuators. The polypyrrole-coated eggshell membrane devices were tested in liquid, ambient atmosphere and controlled humidity environment, with the recorded movements proving their versatility. In 1 M NaCl aqueous solution, by applying successive potential pulses, the actuator contracts/expands owing to the expulsion/insertion of the electrolyte ions out/into polypyrrole film, producing a displacement of similar to 0.1 cm. In air, upon application of voltages from 2 to 5 V on a V-shaped geometry actuator, it bends due to water desorption from its structure induced by Joule heating, generating a displacement which reaches similar to 0.4 cm at 5 V. In a chamber with controlled humidity, the decrease of humidity stimulates a bending/curling motion of the actuator, achieving a displacement of similar to 2.1 cm at 50% relative humidity. Upon modification of the humidity, these actuators move, hold, and release delicate and lightweight objects. Such polypyrrole-coated eggshell membrane actuators which operate in different environments and respond to multiple stimuli can have potential applications in biomimetic micromanipulators or artificial muscle fields.

Bio-waste eggshell membranes (ESM) present a unique micro-architecture consisting in an interwoven fibrous network which can be functionalized with metal oxides resulting in hybrid materials. ESM were covered with ZnO nanostructures by electroless deposition using Au as catalyst. The structural, optical, morphological and wetting properties of the pristine ESM and ESM/ZnO were evaluated. The ESM fibers were uniformly coated by ZnO hexagonal prisms, the hybrid ESM/ZnO preserving the water absorption characteristic of the pristine ESM. Combining an abundant bio-waste with a simple wet chemical synthesis method, flexible organic/inorganic hybrid networks based on ZnO-functionalized ESM can be designed for various applications. (C) 2018 Elsevier B.V. All rights reserved.

In this study, one side aligned PANI coated micro-fibers were fabricated in order to develop a novel actuator configuration. Thus, electrospun PMMA fibers were coated only on one side with a thin gold layer guiding in this way the deposition of PANI (only on the side with gold considering an adequate PANI deposition time). Further, the half-metalized fibers were employed as working microelectrodes for electrochemical deposition of PANI. The prepared PANI coated fibers present actuation properties when they are in contact with an electrolyte like 1 M H2SO4. By switching the potential between +1.4 and -0.2 V, the fiber strips move due to the swelling/shrinking and anisotropic deposition of PANI film.

Morphology is a key element in the functionality of low dimensional structures including here electroactive polymers, especially when applications such as muscle like actuators are sought. The reason is that morphology in the context of a high specific surface object strongly influences specific parameters such as ionic diffusion, conductivity and consequently the actuation capability of the system. In the present work a new architecture for microtube-based actuating elements is presented. Free-standing fibrillar microtubes with diameter in the range of micrometers and with a core-shell polyaniline/gold structure are fabricated through a scalable approach. Aligned electrospun poly(methyl methacrylate) fibers are coated with gold and are further employed as microstructured electrodes for the electrochemical deposition of polyaniline. Further the poly(methyl methacrylate) core was dissolved, leading to a tubular structure. The polyaniline/gold microtubes show complex, rapid and reversible movement patterns, with great stability and consistency over repeated actuation cycles. Thus, when the potential is swept between -0.2 and 1 V at different rates, the microtubes move, this movement being associated with the morphological and structural characteristics of the deposited polyaniline layer, a mechanism based on the expansion/contraction and conformational changes of the polymer chains due to the insertion/expulsion of ions. The response time of these electroactive microstructures during one cycle is in the range of seconds, a consequence of their low dimensionality and specific structure. Moreover the actuation takes place in different electrolytes including simulated gastric fluid, which enables a wide range of applications. (C) 2017 Elsevier B.V. All rights reserved.

The development of soft actuators by using inexpensive raw materials and straightforward fabrication techniques, aiming at creating and developing muscle like micromanipulators, represents an important challenge nowadays. Providing such devices with biomimetic qualities, for example, sensing different external stimuli, adds even more complexity to the task. We developed electroactive polymer coated microribbons that undergo conformational changes in response to external physical and chemical parameters. These were prepared following three simple steps. During the first step nylon-6/6 microribbons were fabricated by electrospinning. In a second step the microribbons were one side coated with a metallic layer. Finally, a conducting layer of polypyrrole was added by means of electrochemical deposition. Strips of polypyrrole-coated aligned microribbon meshes were tested as actuators responding to current, pH, and temperature. The electrochemical activity of the microstructured actuators was investigated by recording cyclic voltammograms. Chronopontentiograms for specific current, pH, and temperature values were obtained in electrolytes with different compositions. It was shown that, upon variation of the external stimulus, the actuator undergoes conformational changes due to the reduction processes of the polypyrrole layer. The ability of the actuator to hold and release thin wires, and to collect polystyrene microspheres from the bottom of the electrochemical cell, was also investigated.

By combining the electrospinning method advantages (high surface-to-volume ratio, controlled morphology, varied composition and flexibility for the resulting structures) with the electrical activity of polyaniline, a new core-shell-type material with potential applications in the field of artificial muscles was synthesized. Thus, a poly(methylmethacrylate) solution was electrospun in optimized conditions to obtain randomly oriented polymer fiber webs. Further, a gold layer was sputtered on their surface in order to make them conductive and improve the mechanical properties. The metalized fiber webs were then covered with a PANI layer by in situ electrochemical polymerization starting from aniline and using sulphuric acid as oxidizing agent. By applying a small voltage on PANI-coated fiber webs in the presence of an electrolyte, the oxidation state of PANI changes, which is followed by the device color modification. The morphological, electrical and biological properties of the resulting multilayered material were also investigated. (C) 2015 Elsevier B.V. All rights reserved.

The electrochemical deposition of ZnxTey thin films was studied in an ionic liquid consisted in choline chloride - ethylene glycol eutectic mixture (Ethaline). ZnCl2 and TeO2 precursors were dissolved in 5-24 millimolar concentrations and the temperature was maintained constant at 60 degrees C. Cyclic voltammograms on Pt from electrolytes with both Te4+ and Zn2+ ions displayed three cathodic processes as limiting currents or peaks: Te underpotential deposition, codeposition of ZnTe compound, and deposition of Zn-rich binary telluride. The corresponding anodic waves or peaks were also identified. The shape of Nyquist electrochemical impedance plots recorded on various applied polarization showed that the electrode first covers with a Te film, and then the more cathodic polarization produces a co-reduction of Te4+ with Zn2+ as ZnTe compound. The formation of Zn metal-rich ZnxTey film at excessive negative polarization is indicated by the lowest value of maximum phase angle in Bode plots. The Zn/Te ratio (apparent stoichiometry) in the films deposited on Cu substrate is controlled by carrying out constant potential electrolyses with different ionic ratios in Ethaline bath. Film morphology, elemental analysis, and crystalline structure were evidenced by SEM microscopy, EDX analysis and X-ray diffraction, respectively.