Biomimetic electrochemistry from conducting polymers. A review

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. Here, we present a different design of the biomimetic electrochromic front that corroborates the electronic and ionic conducting nature of deep reduced films. The direct contact PEDOT metal/electrolyte and film/electrolyte was prevented from electrolyte contact until 1 cm far from the metal contact with protecting Parafilm(®). The deep reduced PEDOT film supports the flow of high currents promoting reaction induced electrochromic color changes beginning 1 cm far from the metal-polymer electrical contact and advancing, through the reduced film, toward the metal contact. Reverse color changes during oxidation/reduction always are initiated at the film/electrolyte contact advancing, under the protecting film, toward the film/metal contact. Both reduced and oxidized states of the film demonstrate electronic and ionic conductivities high enough to be used for electronic applications or, as self-supported electrodes, for electrochemical devices. The electrochemically stimulated conformational relaxation model explains those results.

Facilely tuning the bioactivity of an orthopedic implant surface based on nanostructured polypyrrole/glycosaminoglycans

The wettability of nanostructured polypyrrole/glycosaminoglycans can be controlled in situ by electrical stimulus to tune the bioactivity of implants.

Storing energy in plastics: a review on conducting polymers & their role in electrochemical energy storage

This review article on conducting polymers discusses the background & theory behind their conductivity, the methods to nano-engineer special morphologies & recent contributions to the field of energy (e.g.supercapacitors, batteries and fuel cells).

Insulating and semiconducting polymeric free-standing nanomembranes with biomedical applications

Free-standing nanomembranes, which are emerging as versatile elements in biomedical applications, are evolving from being composed of insulating (bio)polymers to electroactive conducting polymers.

Electroactive polymer–peptide conjugates for adhesive biointerfaces

Conducting-polymer–peptide conjugates with controlled properties have been used as soft bioelectroactive supports for cell attachment.

Multiphoton microfabrication of conducting polymer-based biomaterials

Multiphoton microfabrication was used to prepare CP-based materials for drug delivery and stimulating tissues.

Electrospun rubber fibre mats with electrochemically controllable pore sizes

Electroactive, elastomeric, microfiber mats that show controllable pore size variation upon electrochemical stimulation are produced from semi-interpenetrating polymer networks (s-IPNs).

Elaboration of voltage and ion exchange stimuli-responsive conducting polymers with selective switchable liquid-repellency

In this work, we report the possibility to selectively switch by voltage and anion exchange the water-repellent properties, in comparison with the oil-repellent properties, of copolymers containing both fluorinated chain (EDOT-F8) and pyridinium (EDOT-Py(+)) moieties. Here, the fluorinated chains are necessary to reach superhydrophobic properties while the pyridinium moieties allow the switching in the wettability by counterion exchange. Because, conducting polymers can exist in their oxidized and reduced state, here, we report also the switching of their wettability by voltage. The best properties (superhydrophobic properties with low hysteresis and sliding and good oleophobic properties) are obtained for a % of EDOT-Py(+) of 25 %. Surprisingly, by reducing the polymer by changing the voltage, a selective decrease in the contact angle of water is observed, whereas that of oils (diiodomethane and hexadecane) remain unchanged, making it possible to have higher contact angles with diiodomethane than with water. Here, the switching in the wettability is due to the change of the water droplet from the Cassie-Baxter state to the Wenzel state by changing the voltage. Because of the presence of highly polar pyridinium groups and their perchlorate counterions, the wettability of oil droplets (diiodomethane and hexadecane) is not significantly affected. This effect is confirmed by changing the counterions with highly hydrophobic ones (C8F17SO3(-), Tf2N(-), or BF4(-)). Such materials are excellent candidates for oil/water separation membranes.

Conducting Polypyrrole Nanotube Arrays as an Implant Surface: Fabricated on Biomedical Titanium with Fine-Tunability by Means of Template-Free Electrochemical Polymerization

With the aim of inducing angiogenesis and neurogenesis between implants and bone tissue through electrical signals, conducting polypyrrole (PPy) nanotube arrays (CPNAs) as an implant surface were designed. Large-area CPNAs were fabricated on biomedical titanium by means of template-free electrochemical polymerization based on prenucleation film. The nanoarchitectures were able to be finely tuned between cylindrical and conical nanotubes by tailoring the electrochemical parameters, which were accompanied by a shift in the crystallinity. Accordingly, we propose insight into the fine-tunable fabrication of CPNAs. The prenucleation film possessed a great capability for forming sufficient active nucleation sites that created an isotropic two-dimensional environment, which is a desired medium for facilitating the fabrication of large-area CPNAs on biomedical titanium. Moreover, the fine-tunability of the nanoarchitectures results from the dependency of pyrrole solubility in phosphate buffer solution on the electrochemical conditions.

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.

25th anniversary article: A soft future: from robots and sensor skin to energy harvesters

Scientists are exploring elastic and soft forms of robots, electronic skin and energy harvesters, dreaming to mimic nature and to enable novel applications in wide fields, from consumer and mobile appliances to biomedical systems, sports and healthcare. All conceivable classes of materials with a wide range of mechanical, physical and chemical properties are employed, from liquids and gels to organic and inorganic solids. Functionalities never seen before are achieved. In this review we discuss soft robots which allow actuation with several degrees of freedom. We show that different actuation mechanisms lead to similar actuators, capable of complex and smooth movements in 3d space. We introduce latest research examples in sensor skin development and discuss ultraflexible electronic circuits, light emitting diodes and solar cells as examples. Additional functionalities of sensor skin, such as visual sensors inspired by animal eyes, camouflage, self-cleaning and healing and on-skin energy storage and generation are briefly reviewed. Finally, we discuss a paradigm change in energy harvesting, away from hard energy generators to soft ones based on dielectric elastomers. Such systems are shown to work with high energy of conversion, making them potentially interesting for harvesting mechanical energy from human gait, winds and ocean waves.

Structural electrochemistry. Chronopotentiometric responses from rising compacted polypyrrole electrodes: experiments and model

A model considering conformational packing and structural relaxation–swelling effects describes and quantifies chronopotentiometric responses from conducting polymer film electrodes.

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

Driven reactions, complex ionic exchanges and structural changes are clarified by bending bilayer muscles and corroborated by EDX analysis.