Francesc Estrany

Cellular Adhesion, Proliferation and Viability on Conducting Polymer Substrates

This work reports a comprehensive study about cell adhesion and proliferation on the surface of different electroactive substrates formed by pi-conjugated polymers. Biological assays were performed considering four different cellular lines: two epithelial and two fibroblasts. On the other hand, the electroactivity of the three conducting systems was determined in physiological conditions. Results indicate that the three substrates behave as a cellular matrix, even though compatibility with cells is larger for PPy and the 3-layered system. Furthermore, the three polymeric systems are electro-compatible with the cellular monolayers.

Nanostructured conducting polymer for dopamine detection

In this work, we demonstrate the ability of poly(N-methylpyrrole) to form nanostructures and to detect very low concentrations of dopamine, an important neurotransmitter. Poly(N-methylpyrrole) hollow particles of controlled thickness have been prepared using the layer-by-layer assembly technique and polystyrene core-shell particles as templates, which are subsequently eliminated to yield free-standing hollow microspheres with a layer thickness of 30 nm. The morphology and composition of these structures have been evaluated by scanning electron microscopy, transmission electron microscopy, FTIR, Raman and X-ray photoelectron spectroscopies. Results demonstrate that intact hollow spheres can be obtained controlling the number of polymer deposition cycles. Furthermore, two kind of sensors were constructed by immobilizing poly(N-methylpyrrole)/Au nanocomposites and poly(N-methylpyrrole) nanomembranes on the surface of a glassy carbon electrode. Electrochemical techniques were employed to evaluate the ability of poly(N-methylpyrrole) to absorb/immobilize dopamine molecules. It was found that systems based on this conducting polymer are highly sensitive to the neurotransmitter concentration, presenting a very fast response even when the concentration of the dopamine is very low.

Hybrid polythiophene–clay exfoliated nanocomposites for ultracapacitor devices

Exfoliated nanocomposites of poly(3,4-ethylenedioxythiophene) (PEDOT) and montmorillonite (MMT) have been prepared by in situ anodic polymerization, concentrations of clay ranging from 5% w/w to 50% w/w being included in the aqueous polymerization medium. The morphology, electrical conductivity, adherence, thermal stability, charge storage, specific capacitance, electrostability, doping level and band gap have been determined for the different PEDOT–MMT nanocomposites and compared with those of pristine PEDOT. Many of these properties have been found to depend on both the concentration of clay and the thickness (micrometric or nanometric) of the generated films. Types I and II ultracapacitors have been fabricated using nanometric and micrometric films of PEDOT and PEDOT–MMT. The properties of such devices have been characterized and compared with those reported in the literature for ultracapacitors fabricated using nanocomposites of PEDOT and other inorganic materials. Both nanometric and micrometric type II ultracapacitors, which correspond to an asymmetric configuration of PEDOT and PEDOT–MMT films, have been found to present the better properties (e.g. the specific capacitance for nanometric and micrometric devices is 429 and 116 F g−1, respectively), evidencing the favorable effect of the clay. Finally, the effects of the electrochemical degradation on the ultracapacitors have been rationalized using electrochemical impedance spectroscopy.

Towards sustainable solid-state supercapacitors: electroactive conducting polymers combined with biohydrogels

Solid-state organic electrochemical supercapacitors (OESCs) have been fabricated using poly(3,4-ethylenedioxythiophene) (PEDOT) electrodes, a biohydrogel as electrolyte system, and polyaniline fibers as redox additive. The effectivity of sodium alginate, κ-carrageenan, chitosan and gelatin hydrogels as electrolytic media has been evaluated considering different criteria. Results indicate that κ-carrageenan-based hydrogel is the most suitable to perform as electrolyte due to the appropriate combination of properties: mechanical stability, ease of preparation, lack of water leaking, and good medium for the electrochemical response of PEDOT electrodes. Cyclic voltammetry and galvanostatic charge–discharge assays indicate that OESCs based on PEDOT electrodes and κ-carrageenan hydrogel as electrolyte exhibits a good supercapacitor response in terms of specific capacitance, cycling stability, small leakage current and low self-discharging tendency. On the basis of these good properties, four OESC devices were assembled in series and used to power a red LED, confirming that, in addition to advantageous characteristics (e.g. elimination of liquid leaking and enhancement of the device compactness), the designed biohydrogel-containing OESC exhibits potential for practical applications. On the other hand, preliminary assays have been performed loading the κ-carrageenan hydrogel with polyaniline nanofibers, which act as a redox additive. OESC devices prepared using such loaded biohydrogel have been found to be very promising and, therefore, future work is oriented towards the improvement of their design.

Bioactive and electroactive response of flexible polythiophene:polyester nanomembranes for tissue engineering

Properties of free-standing nanomembranes prepared by blending poly(3-thiophene methyl acetate) and poly(tetramethylene succinate), a soluble polythiophene derivative and a biodegradable polyester, respectively, have been examined. The outstanding flexibility and robustness of the nanomembranes floating in ethanol have been demonstrated through aspiration in pipette/release/shape recovery cycles, which were repeated without cracking the film. The blend retains the electrochemical properties (i.e. oxidation and reduction processes) of the individual conducting polymer in both physiological and organic environments. Hydrolytic and enzymatic degradation assays show that the degradation of the polyester domains produces the detachment of the conducting polymer domains. The cellular viability, which has been studied using four different cellular lines, is significantly higher for the blend than for the polyester, indicating that the former material is a potential bioactive platform for tissue engineering. Finally, the electrobioactivity of the individual materials and the blend coated with cellular monolayers shows some dependence on the cellular line.

Poly(2-thiophen-3-yl-malonic acid), a polythiophene with two carboxylic acids per repeating unit.

A new substituted polythiophene derivative bearing malonic acid, poly(2-thiophen-3-yl-malonic acid), has been prepared and characterized using a strategy that combines both experimental and theoretical methodologies. The chemical structure of this material has been investigated using FTIR and (1)H NMR, and its molecular conformation has been determined using quantum mechanical calculations. Interestingly, the arrangement of the inter-ring dihedral angles was found to depend on the ionization degree of the material, that is, on the pH, which has been found completely soluble in aqueous base solution. Thus, the preferred anti-gauche conformation changes to syn-gauche when the negatively charged carboxylate groups transforms into neutral carboxylic acid. UV-vis experiments and quantum mechanical calculations on model systems with a head-to-tail regiochemistry showed that the lowest pi-pi* transition energy is 2.25 and 2.39 eV for the negatively charged and the neutral polymer, respectively. These values are slightly larger than those previously reported for other polythiophenes with bulky polar side groups. The polymer presents a good thermal stability with a decomposition temperature above 215 degrees C and an electrical conductivity of 10(-5) S/cm, which is characteristic of semiconductor materials. Scanning electron microscopy micrographs showed that, after doping, the surface of this material displays regular distribution pores with irregular sizes. This surface suggests that poly(2-thiophen-3-yl-malonic acid) is a candidate for potential applications such as selective membranes for electrodialysis, wastewater treatment, or ion-selective membranes for biomedical uses.

Electropolymerization of 2,5-di-(-2-thienyl)-pyrrole in ethanolic medium. Effect of solution stirring on doping with perchlorate and chloride ions

Abstract The electrochemical behavior of 2,5-di-(-2-thienyl)-pyrrole (SNS) on Pt has been studied from a 10 mM monomer solution in 0.2 M LiClO 4 +ethanol or in 0.2 M LiCl+ethanol by cyclic voltammetry, chronopotentiometry and chronoamperometry. The monomer exhibits two similar consecutive oxidation processes. Uniform, adherent and electroactive films of dark-blue poly(SNS) doped with ClO 4 − or with Cl − are obtained at low potentials related to the first process. Reproducible film weights are found at 0.700 V versus Ag|AgCl during 360 s. The increase in transport rate of reactants by stirring the solution with a magnetic bar at 150 rpm accelerates the SNS electropolymerization, allowing to collect much more polymer weight than from the quiescent solution. The productivity of poly(SNS) doped with Cl − determined by ‘ex situ’ ultramicrogravimetry increases notably under stirring, although its percentage in Cl − is similar to that found under quiescent conditions. This is ascribed to the production of a major proportion of longer linear molecules in polymer, consistent with its higher conductivity when it is synthesized under stirring. This effect is not so clear for the poly(SNS) doped with ClO 4 − due to the little influence of stirring upon its productivity and conductivity. The detection of short linear oligomers in the soluble fractions of polymers in thioglycerol by mass spectrometry-fast atom bombardment allows to propose a radical polycondensation as initial electropolymerization mechanism.

Hybrid materials consisting of an all-conjugated polythiophene backbone and grafted hydrophilic poly(ethylene glycol) chains

Organic hybrid materials consisting of an all-conjugated polythiophene backbone and well-defined poly(ethylene glycol) (PEG) grafted chains have been prepared by anodic polymerization of chemically synthesized macromonomers. The latter consist of a pentathiophene sequence in which the central ring bears a PEG chain with Mw = 1000 or 2000 at the 3-position. The influence of the polymerization potential, the length of the PEG branches and the dopant agent on the structure and properties of the graft copolymers has been examined. The chemical structure of the grafted materials has been corroborated by FTIR and X-ray photoelectron spectroscopies. Scanning electron microscopy and atomic force microscopy studies reveal that the morphology and topography of these materials are influenced by the above mentioned factors, even though homogeneous films showing a compact distribution of nanoaggregates, very flat surfaces (i.e. roughness < 15 A) and nanometric thickness (i.e. 100–500 nm) were obtained in all cases. Cyclic voltammetry assays have been used to determine the presence of charged species, the electroactivity, the electrostability and the formation of cross-links. The electrochemical stability of the copolymer with grafted PEG chains of Mw = 1000 has been found to increase with the number of consecutive oxidation–reduction cycles (self-electrostabilizing behavior). Finally, a preliminary investigation into the applicability of these hybrid materials as active surfaces for the selective adsorption of proteins is presented.

Detection of Dopamine Using Chemically Synthesized Multilayered Hollow Microspheres

Microspheres made of alternating layers of two different conducting polymers, poly(3,4-ethylenedioxythiophene) and poly(N-methylpyrrole), have been found to be sensitive to dopamine (DA) oxidation, presenting a very well-defined and linear response in the range of DA concentrations from 0.5 to 2 mM. The novelty of the present study is the use of doped multilayered hollow microspheres, which are prepared by successive oxidative chemical polymerizations in FeCl3 aqueous solution. The multilayered microspheres were characterized by FTIR and UV-visible spectroscopies, scanning and transmission electron microscopies, and atomic force microscopy. The UV-visible bands confirm that the multilayered system is not well doped with FeCl4(-) counterions. Therefore, the doping level was increased by further oxidation with LiClO4 before DA electrochemical detection. Despite that the range of concentration detection was limited from 0.5 mM to 2 mM, doped hollow multilayered microspheres show a very good anodic peak current response compared to single-layer films fabricated with an individual conducting polymer and activated by gold nanoparticles.

Poly(3,4-ethylenedioxythiophene) on self-assembled alkanethiol monolayers for corrosion protection

Self-assembled monolayers (SAMs) of octanethiol and dodecanethiol were used to modify the stainless steel substrates for electrodepositing poly(3,4-ethyledioxythiophene) (PEDOT), a well known polythiophene derivative. Although the influence of the alkanethiol monolayers on the morphology and topology of micrometric (thickness: 2.25–2.35 μm) PEDOT films is practically negligible, they increase significantly the ability to store charge and the adherence. In contrast, treated substrates not only enhance the electrochemical properties of ultra-thin PEDOT films (thickness: 150–350 nm) but also affect significantly the thickness, roughness, porosity, morphology and topology. Such changes depend on both the length of the alkyl chain in the alkanethiol and the incubation period used for the preparation of the SAMs. Finally, the protection against corrosion imparted by PEDOT films deposited on treated substrates has been examined and compared with that obtained using PEDOT deposited on bare stainless steel electrodes. Inhibition of the corrosion in a 3.5% NaCl solution was found to be considerably higher when PEDOT is deposited on treated electrodes, which has been attributed, in addition to the barrier effect produced by the SAMs, to the structural changes induced at the first stages of the electropolymerization.