Conducting‐Polymer Nanotubes Improve Electrical Properties,Mechanical Adhesion,Neural Attachment,and Neurite Outgrowth of Neural Electrodes

An in vitro comparison of conducting‐polymer nanotubes of poly(3,4‐ethylenedioxythiophene) (PEDOT) and poly(pyrrole) (PPy) and to their film counterparts is reported. Impedance, charge‐capacity density (CCD), tendency towards delamination, and neurite outgrowth are compared. For the same deposition charge density, PPy films and nanotubes grow relatively faster vertically, while PEDOT films and nanotubes grow more laterally. For the same deposition charge density (1.44 C cm^?2), PPy nanotubes and PEDOT nanotubes have lower impedance (19.5 ± 2.1 kΩ for PPy nanotubes and 2.5 ± 1.4 kΩ for PEDOT nanotubes at 1 kHz) and higher CCD (184 ± 5.3 mC cm^?2 for PPy nanotubes and 392 ± 6.2 mC cm^?2 for PEDOT nanotubes) compared to their film counterparts. However, PEDOT nanotubes decrease the impedance of neural‐electrode sites by about two orders of magnitude (bare iridium 468.8 ± 13.3 kΩ at 1 kHz) and increase capacity of charge density by about three orders of magnitude (bare iridium 0.1 ± 0.5 mC cm^?2). During cyclic voltammetry measurements, both PPy and PEDOT nanotubes remain adherent on the surface of the silicon dioxide while PPy and PEDOT films delaminate. In experiments of primary neurons with conducting‐polymer nanotubes, cultured dorsal root ganglion explants remain more intact and exhibit longer neurites (1400 ± 95 µm for PPy nanotubes and 2100 ± 150 µm for PEDOT nanotubes) than their film counterparts. These findings suggest that conducting‐polymer nanotubes may improve the long‐term function of neural microelectrodes.     

A Review of Organic and Inorganic Biomaterials for Neural Interfaces

Recent advances in nanotechnology have generated wide interest in applying nanomaterials for neural prostheses. An ideal neural interface should create seamless integration into the nervous system and performs reliably for long periods of time. As a result, many nanoscale materials not originally developed for neural interfaces become attractive candidates to detect neural signals and stimulate neurons. In this comprehensive review, an overview of state‐of‐the‐art microelectrode technologies provided first, with focus on the material properties of these microdevices. The advancements in electro­active nanomaterials are then reviewed, including conducting polymers, carbon nanotubes, graphene, silicon nanowires, and hybrid organic‐inorganic nanomaterials, for neural recording, stimulation, and growth. Finally, technical and scientific challenges are discussed regarding biocompatibility, mechanical mismatch, and electrical properties faced by these nanomaterials for the development of long‐lasting functional neural interfaces.     

Influence of Biodopants on PEDOT Biomaterial Polymers: Using QCM‐D to Characterize Polymer Interactions with Proteins and Living Cells

Organic conducting polymers (OCPs) are currently the subject of intense research in the area of biomaterials and bioelectronics. Of the OCPs, poly(3,4‐ethylenedioxythiophene) (PEDOT) has attracted significant interest, however there has been little work on investigating the incorporation of biological compounds as the dopant species in the polymer which are aimed at enhancing the biocompatibility and biofunctionality of the material. Here, we incorporate the biological dopants dextran sulphate, chondroitin sulphate, and alginate, into PEDOT polymers and investigate their influence on a suite of physicochemical and electrochemical properties. We employ QCM‐D to study the mass of adsorption and the viscoelastic properties of the important extracellular matrix proteins fibronectin and collagen. Furthermore, we use QCM‐D to study the adhesion of PC12 neural cells to the PEDOT‐biodopant polymers with and without an adsorbed protein conditioning layer. QCM‐D was found to be an excellent tool with which to study conducting polymer–biological interactions, with this report the first time that QCM‐D has been used to study cell interactions with conducting polymer biomaterials.     

High‐Density Stretchable Electrode Grids for Chronic Neural Recording

Electrical interfacing with neural tissue is key to advancing diagnosis and therapies for neurological disorders, as well as providing detailed information about neural signals. A challenge for creating long‐term stable interfaces between electronics and neural tissue is the huge mechanical mismatch between the systems. So far, materials and fabrication processes have restricted the development of soft electrode grids able to combine high performance, long‐term stability, and high electrode density, aspects all essential for neural interfacing. Here, this challenge is addressed by developing a soft, high‐density, stretchable electrode grid based on an inert, high‐performance composite material comprising gold‐coated titanium dioxide nanowires embedded in a silicone matrix. The developed grid can resolve high spatiotemporal neural signals from the surface of the cortex in freely moving rats with stable neural recording quality and preserved electrode signal coherence during 3 months of implantation. Due to its flexible and stretchable nature, it is possible to minimize the size of the craniotomy required for placement, further reducing the level of invasiveness. The material and device technology presented herein have potential for a wide range of emerging biomedical applications.     

A Template‐Free Method Towards Conducting Polymer Nanostructures

Conducting polymer nanostructures have recently received special attention in nanoscience and nanotechnology because of their highly π‐conjugated polymeric chains and metal‐like conductivity, such that they can be regarded not only as excellent molecular wires, but also as basic units for the formation of nanodevices. Although various approaches, such as hard‐template methods, soft‐template methods, electrospinning technology, and so on are widely employed to synthesize or fabricate conducting polymer nanostructures and their composite nanostructures, each of the currently used methods possess disadvantages. Therefore, finding a facile, efficient, and controlled method of forming conducting polymer nanostructures is desirable. Similar to other nanomaterials, the effect of size (in these cases 1–100 nm) on the properties of the conducting polymer nanostructures must be considered. Electrical measurements of single nanotubes or nanowires are desirable in order to be able to understand the pure electrical properties of conducting polymer nanostructures. Compared with bulk conducting polymers, conducting polymer nanostructures are expected to display improved performance in technological applications because of the unique properties arising from their nanometer‐scaled size: high conductivity, large surface area, and light weight. Thus, it is also desirable to develop promising applications for conducting polymer nanostructures. In accordance with the issues described above, our research focuses on a new synthesis method to form conducting polymer nanostructures and on the related formation mechanism of the resultant nanostructures. The electrical and transport properties of single nanotubes of conducting polymer, measured by a four‐probe method, and promising applications of such template‐free‐synthesized conducting polymer nanostructures as new microwave absorbing materials and sensors guided by a reversible wettability are also of interest. This article reports some of our main results and reviews some important contributions of others.

     

Approaching Intra‐ and Interchain Charge Transport of Conjugated Polymers Facilely by Topochemical Polymerized Single Crystals

Charge transport of small molecules is measured well with scanning tunneling microscopy, conducting atomic force microscopy, break junction, nanopore, and covalently bridging gaps. However, the manipulation and measurement of polymer chains remain a long‐standing fundamental issue in conjugated polymers and full of challenge since conjugated polymers are naturally disordered materials. Here, a fundamental breakthrough in generating high‐quality conjugated‐polymer nanocrystals with extended conjugation and exceptionally high degrees of order using a surface‐supported topochemical polymerization method is demonstrated. In the crystal the conjugated‐polymer chains are extended along the long axis of the crystal with the side chains perpendicular to the long axis. Devices with conducting channels along the polymer chains show efficient charge transport, nearly two orders of magnitude greater than the interchain charge transport along the π–π stacking direction. This is the first example to clarify intra‐ and interchain charge transport based on an individual single crystal of conjugated polymers, and demonstrate the importance of intrachain charge transport in plastic electronics.     

Applikationsfelder organischer Funktionspolymere,Polymeraktoren und Polymertransistoren

Prospective application fields of organic functional polymers, polymer actuators and transistors The paper gives a short survey of prospective high tech products in which conducting polymers and other polymers with special electronic properties will be applied. Such products are, for example, polymer actuators, organic field effect transistors (OFET's) and integrated plastic circuits, organic light emitting diodes (OLED's), plastic solar or photovoltaic cells, membranes for fuel cells, polymer batteries and various polymer sensors. It will be informed about structures and properties of intrinsic conducting polymers and more in detail on electro‐chemo‐mechanical polymer actuators and on polymeric field effect transistors.     

Strong,Conductive, Foldable Graphene Sheets by Sequential Ionic and π Bridging

The goal of this work is to develop an inexpensive low‐temperature process that provides polymer‐free, high‐strength, high‐toughness, electrically conducting sheets of reduced graphene oxide (rGO). To develop this process, we have evaluated the mechanical and electrical properties resulting from the application of an ionic bonding agent (Cr³⁺), a π–π bonding agent comprising pyrene end groups, and their combinations for enhancing the performance of rGO sheets. When only one bonding agent was used, the π–π bonding agent is much more effective than the ionic bonding agent for improving both the mechanical and electrical properties of rGO sheets. However, the successive application of ionic bonding and π–π bonding agents maximizes tensile strength, toughness, long‐term electrical stability in various corrosive solutions, and resistance to mechanical abuse and ultrasonic dissolution. Using a combination of ionic bonding and π–π bonding agents, high tensile strength (821 MPa), high toughness (20 MJ m^?3), and electrical conductivity (416 S cm^?1) were obtained, as well as remarkable retention of mechanical and electrical properties during ultrasonication and mechanical cycling by both sheet stretch and sheet folding, suggesting high potential for applications in aerospace and flexible electronics.     

Organische Polymere als funktionelle Werkstoffe für chemische Sensoren

Organic polymers as functional materials for chemical sensors The function of many chemical sensors for measurements in liquids and in gases with ambient temperature is based on the combination of a transducer with organic membranes. These membrans determine essential sensor properties as selectivity, sensitivity and response characteristics. In addition they protect the detection system against external influences. Therefore the selection and synthesis of polymer membranes are an essential constituent of the sensor investigation and sensor development. Electrical, optical and biological properties of the polymers are important in this case. A survey of the materials used in the remote sensing is given. Of special interest to the sensor investigation are in last time intrinsic conducting polymers (ILP) whose properties opened new possibilities of the sensor development. With the help of an electrochemical pH glass electrode with inner solid contact it is shown that polypyrrole can be used as a material for a long‐lived inner solid contact and as substitute for inner secondary reference electrode. Practice tests confirm the suitability of this polymer material. Aspects of the transport mechanism of electrical charges through the boundary surface conducting polymer | glass are discussed.     

Functionalized Conducting Polymer Nano‐Networks from Controlled Oxidation Polymerization toward Cell Engineering

In this work we present a general approach for bulk synthesis of various functionalized conducting polymer nano‐networks. 3,4‐ethylenedioxythiophene (EDOT) dimers are used to initiate the chemical polymerization of functionalized EDOT in the solvent system with high polarity, which leads to better control of the oxidation polymerization. Under these reaction conditions, various functionalized EDOT monomers form polymeric nano‐network structures. We also evaluate the cell growth and cell viability on these conducting polymer nano‐networks. The nano‐networks provide highly biocompatible materials for PC12 cells and they show nice attachment on the surface. These properties of functionalized conducting polymer nano‐networks indicate a promising platform for cell engineering.     

Organische Funktionsschichten in Polymerelektronik und Polymersolarzellen

Organic functional layers in polymer electronics and polymer solar cells Thin layers of organic functional polymers play the predominant role in polymer electronics like organic field effect transistors (OFET's) and in organic photovoltaic devices. The well‐known advantages of these solution‐processable materials opened the way for their welcoming now in application fields, which were fully occupied by inorganic semiconductors in the past. However, the polymer semiconductors show also some disadvantages, like a relatively low charge carrier mobility and a not yet sufficient long‐term stability. However, fore the aim of R&D for polymer electronics is not the replace of well‐tried electronic materials and technologies but the opening of new application fields for the new kind of low‐cost /low‐performance electronics. The paper presents recent results of OFET's with thin layers from conjugated polymers like poly(3‐alkylthiophenes), as active semiconducting material, and poly(4‐vinylphenol) as gate dielectricum. Experiments concerning generation of source‐drain electrodes based on polyaniline or Baytron P by laser ablation are represented. Additionally, printing techniques or laser modification are used for patterning of conducting polymers. The described polymer solar cells use for the photoactive layer a composite from polyalkylthiophenes, as light absorbing and charge generating polymer, and fullerene derivatives, responsible for fast electron transfer. Donator‐acceptor cells containing substituted fullerenes give also internationally the best efficiency with η ≈ 3%.     

Bioinspired Ultrastrong Solid Electrolytes with Fast Proton Conduction along 2D Channels

Solid electrolytes have attracted much attention due to their great prospects in a number of energy‐ and environment‐related applications including fuel cells. Fast ion transport and superior mechanical properties of solid electrolytes are both of critical significance for these devices to operate with high efficiency and long‐term stability. To address a common tradeoff relationship between ionic conductivity and mechanical properties, electrolyte membranes with proton‐conducting 2D channels and nacre‐inspired architecture are reported. An unprecedented combination of high proton conductivity (326 mS cm^?1 at 80 °C) and superior mechanical properties (tensile strength of 250 MPa) are achieved due to the integration of exceptionally continuous 2D channels and nacre‐inspired brick‐and‐mortar architecture into one materials system. Moreover, the membrane exhibits higher power density than Nafion 212 membrane, but with a comparative weight of only ≈0.1, indicating potential savings in system weight and cost. Considering the extraordinary properties and independent tunability of ion conduction and mechanical properties, this bioinspired approach may pave the way for the design of next‐generation high‐performance solid electrolytes with nacre‐like architecture.     

Gadolinium Metallofullerene‐Based Activatable Contrast Agent for Tumor Signal Amplification and Monitoring of Drug Release

Activatable imaging probes are promising to achieve increased signal‐to‐noise ratio for accurate tumor diagnosis and treatment monitoring. Magnetic resonance imaging (MRI) is a noninvasive imaging technique with excellent anatomic spatial resolution and unlimited tissue penetration depth. However, most of the activatable MRI contrast agents suffer from metal ion‐associated potential long‐term toxicity, which may limit their bioapplications and clinical translation. Herein, an activatable MRI agent with efficient MRI performance and high safety is developed for drug (doxorubicin) loading and tumor signal amplification. The agent is based on pH‐responsive polymer and gadolinium metallofullerene (GMF). This GMF‐based contrast agent shows high relaxivity and low risk of gadolinium ion release. At physiological pH, both GMF and drug molecules are encapsulated into the hydrophobic core of nanoparticles formed by the pH‐responsive polymer and shielded from the aqueous environment, resulting in relatively low longitudinal relativity and slow drug release. However, in acidic tumor microenvironment, the hydrophobic‐to‐hydrophilic conversion of the pH‐responsive polymer leads to amplified MR signal and rapid drug release simultaneously. These results suggest that the prepared activatable MRI contrast agent holds great promise for tumor detection and monitoring of drug release.     

Hierarchical organization of Au nanoparticles in a poly(vinyl carbazole) matrix for hybrid electronic devices

We report a novel one-step method for the preparation of hierarchically patterned Au nanoparticles in a conducting polymer matrix by controlling the interface properties between Au nanoparticles and the conducting polymer matrix. The terminal group of capping molecules for the Au nanoparticles was modified to change the interface properties, not to change the size of the Au nanoparticles which affects their intrinsic properties. By modulating the interface properties, it is possible to construct Au nanoparticle-conducting polymer composites with two different structures: one presents a triple layer in which the conducting polymer layer is sandwiched between Au nanoparticle layers at the top and bottom; the other exhibits a form like a raisin cake in which Au nanoparticles are homogeneously organized in the conducting polymer matrix. High-resolution transmission electron microscopy was used to study the morphology and patterning of Au?nanoparticles in the conducting polymer matrix.     

Highly Deformable and See‐Through Polymer Light‐Emitting Diodes with All‐Conducting‐Polymer Electrodes

Despite the high expectation of deformable and see‐through displays for future ubiquitous society, current light‐emitting diodes (LEDs) fail to meet the desired mechanical and optical properties, mainly because of the fragile transparent conducting oxides and opaque metal electrodes. Here, by introducing a highly conductive nanofibrillated conducting polymer (CP) as both deformable transparent anode and cathode, ultraflexible and see‐through polymer LEDs (PLEDs) are demonstrated. The CP‐based PLEDs exhibit outstanding dual‐side light‐outcoupling performance with a high optical transmittance of 75% at a wavelength of 550 nm and with an excellent mechanical durability of 9% bending strain. Moreover, the CP‐based PLEDs fabricated on 4 µm thick plastic foils with all‐solution processing have extremely deformable and foldable light‐emitting functionality. This approach is expected to open a new avenue for developing wearable and attachable transparent displays.     

Bio‐Interface of Conducting Polymer‐Based Materials for Neuroregeneration

Nerve system diseases like Parkinson's disease, Huntington's disease, Alzheimer's disease, etc. seriously affect thousands of patients' lives every year, making them suffer from pains and inconvenience. Recently, bio‐interfaces between neural cells/tissues and polymer based biomaterials attracted worldwide attention due to the ability of polymer based biomaterials to serve as nerve conduits, drug carriers and neurites guidance platform in neuroregeneration. The role that bio‐interface played and the way it interacted with neural tissues and cells have been thoroughly investigated by the researchers. In this paper we mainly focus on reviewing the bio‐interface between nerve tissues/cells and advanced functional biocompatible polymers, such as conducting polymers and advanced carbon composite materials. These advanced polymers can provide combined interfacial stimulations including interfacial external neurotrophic factors (NTFs) delivery, electrical stimulation, surface guidance and molecules decoration to lesion cells and tissues to promote neuroregeneration in vitro and in vivo, and have contributed greatly to nerve diseases therapy. At the end of this review, the criteria of polymer based biomaterials utilized in neuroregeneration are summarized and the perspectives for future development of bio‐interfaces are also discussed.     

Polymer Brushes on Hexagonal Boron Nitride

Direct covalent functionalization of large‐area single‐layer hexagonal boron nitride (hBN) with various polymer brushes under mild conditions is presented. The photopolymerization of vinyl monomers results in the formation of thick and homogeneous (micropatterned, gradient) polymer brushes covalently bound to hBN. The brush layer mechanically and chemically stabilizes the material and allows facile handling as well as long‐term use in water splitting hydrogen evolution reactions.     

A poly(cyclopentadithiophene) matrix suitable for electrochemically controlled DNA delivery

A conducting polymer is tested for DNA delivery trials. The conducting matrix used is successful for electrochemical delivery of DNA accumulated by covalent immobilization. The electrochemical process consists of the reduction of arylsulfonamide moieties, which occur as linker groups. The specific design of the polymer allows the electronic properties to be promoted, making available the cleavage potential in physiological media. The amount of DNA released from a modified platinum electrode is investigated by quartz crystal microbalance. The released species used to prove the system performance are long sequences of DNA strands, which are amplified by PCR after liberation and identified by electrophoresis migration.     

Flexible and Implantable Microelectrodes for Chronically Stable Neural Interfaces

Implantable electrical probes that can record neural activities at single‐neuron and sub‐millisecond resolution are the most widely applied tools in both neuroscience research and neuroprosthetics. However, the structural and mechanical mismatch between conventional rigid probes and neural tissues results in inflammatory responses and signal degradation over chronic recordings. Reducing the cross‐sectional footprints and rigidity of the probes can effectively improve the long‐term stability of neural interfaces. Herein, recent progress in the development of implantable microelectrodes for chronically stable neural interfaces is highlighted, with a focus on the utilization of advanced materials and structural design concepts.     

Black Phosphorus Nanosheets Passivation Using a Tripeptide

In the past several years, 2D black phosphorus (BP) has captured the research community's interest because of its unique electronic, photonic, and mechanical properties. However, the intrinsic instability of BP limits its preservation and practical application. Despite kinds of BP passivation strategies being well‐documented, the use of metal ligand coordination or polymer modification may have potential long‐term detrimental effects on human bodies. Here, a tailored tripeptide Fmoc‐Lys‐Lys‐Phe (Fmoc‐KKF) is synthesized for surface modification of BP nanosheets. Compared with bare BP with rapid degradation, the BP@FKK complex exhibits excellent stability, thereby significantly increasing the life span. Significantly, the BP@FKK shows favorable cell compatibility and enhanced cellular uptake compared to the bare BP.