Conducting Polymer Substrate Research Articles

Accelerated osteoblast mineralization on a conductive substrate by multiple electrical stimulation

One of the major benefits of a conductive PPy-based substrate is that the mediated electrical stimulation (ES) can be a stimulating factor to promote tissue regeneration. We cultured osteoblast-like Saos-2 cells on a conductive substrate made of biodegradable polylactide (95 wt%) and electrically conducting polypyrrole bioactivated with heparin (PPy/HE) (5 wt%). Using multi-well electrical cell culture plates, the effect of multiple ESs on osteoblast mineralization was investigated at various culture times. As ascertained by ARS, CPC and XPS analyses, the ES was able to promote osteoblast adhesion and growth, resulting in significantly higher calcium and phosphate content in the mineral deposition of the electrically stimulated membranes. Morphology, Ca/P ratio and crystalline structure demonstrated that the minerals on the conductive substrate surface were similar to those found on typical hydroxyapatite. ES also significantly upregulated the expression of the osteoblast-specific markers ALP, BMP2, Runx2 and OC. ES through a synthetic conductive polymer substrate therefore represents a vital option to promote bone regeneration.

Atomic Force Microscopy Studies of Carbon Nitride (CNx) Films Deposited on a Conducting Polymer Substrate

Carbon nitride films were deposited onto indium tin oxide and undoped polybithiophene substrates using direct-current reactive magnetron sputtering. The local morphology and electronic properties of the deposited films were investigated using phase-imaging (PI-AFM) and current-sensing atomic force microscopy (CS-AFM). The deposited materials were found to be generally amorphous with many individual nanostructured bonding domains. The nature of the substrate was found to have a significant effect on the microscopic distribution of carbon nitride regions with the carbon nitride films showing some long-range order when deposited onto an undoped polybithiophene substrate.

Complex Surface Concentration Gradients by Stenciled ”Electro Click Chemistry”

Complex one- or two-dimensional concentration gradients of alkynated molecules are produced on azidized conducting polymer substrates by stenciled "electro click chemistry". The latter describes the local electrochemical generation of catalytically active Cu(I) required to complete a "click reaction" between alkynes and azides at room temperature. A stencil on the counter electrode defines the shape and multiplicity of the gradient(s) on the conducting polymer substrate, while the specific reaction conditions control gradient steepness and the maximum concentration deposited. Biologically active ligands including cell binding peptides are patterned in gradients by this method without losing their biological function or the conductivity of the polymer.

Making high-fidelity imprint template by resist patterns over a flexible conductive polymer substrate

A technique to fabricate an imprint template is proposed, based on a direct replication of the electronic-beam lithography resist patterns over a flexible conductive polymer substrate. This approach will simplify the template-making process because no anisotropic dry etching is required to transfer the resist pattern into a template material as usual. The flexible polymer film used as the substrate will be helpful during the detaching step of the template obtained; moreover, the flexibility of the substrate can be used to fabricate templates with curved-surface patterns. Using the technique, both the polymer templates and metal templates can be fabricated, and the above advantages will allow the templates to obtain the high-fidelity patterns directly from the electronic-beam lithography.

Wet‐Spun Biodegradable Fibers on Conducting Platforms: Novel Architectures for Muscle Regeneration

AbstractNovel biosynthetic platforms supporting ex vivo growth of partially differentiated muscle cells in an aligned linear orientation that is consistent with the structural requirements of muscle tissue are described. These platforms consist of biodegradable polymer fibers spatially aligned on a conducting polymer substrate. Long multinucleated myotubes are formed from differentiation of adherent myoblasts, which align longitudinally to the fiber axis to form linear cell‐seeded biosynthetic fiber constructs. The biodegradable polymer fibers bearing undifferentiated myoblasts can be detached from the substrate following culture. The ability to remove the muscle cell‐seeded polymer fibers when required provides the means to use the biodegradable fibers as linear muscle‐seeded scaffold components suitable for in vivo implantation into muscle. These fibers are shown to promote differentiation of muscle cells in a highly organized linear unbranched format in vitro and thereby potentially facilitate more stable integration into recipient tissue, providing structural support and mechanical protection for the donor cells. In addition, the conducting substrate on which the fibers are placed provides the potential to develop electrical stimulation paradigms for optimizing the ex vivo growth and synchronization of muscle cells on the biodegradable fibers prior to implantation into diseased or damaged muscle tissue.

Electronic non-equilibrium conditions at C 60–pentacene heterostructures

The electronic structure of vacuum-sublimed layered organic heterostructures of pentacene (PEN) and fullerene (C 60) on conducting polymer substrates was investigated using ultraviolet photoelectron spectroscopy (UPS). The conditions at the PEN/C 60interface changed from thermodynamic non-equilibrium (i.e. the onset of the PEN highest occupied molecular orbital above the substrate Fermi-energy) for thin PEN coverages on C 60 to thermodynamic equilibrium for thicker PEN coverages (i.e. Fermi-level pinning of PEN). This finding is attributed to a coverage-dependent pinhole connection of PEN through the C 60 layer with the substrate. The experiments demonstrate the importance of organic thin film morphology for UPS measurements to assess the energy level alignment at organic/organic heterointerfaces.

Structural and electronic properties of pentacene-fullerene heterojunctions

In this study the performance differences of layered and bulk-heterojunction based organic solar cells composed of the prototypical p- and n-type organic semiconductors pentacene (PEN) and fullerene (C60) are correlated with the physical properties of the heterostructures. The electronic structure of layered and codeposited thin PEN and C60 films on the conducting polymer substrate poly(ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) was investigated with ultraviolet photoelectron spectroscopy. Layered structures of C60 on PEN precovered PEDOT:PSS exhibited an offset of the highest occupied molecular orbital (HOMO) levels of 1.45 eV. In contrast, codeposited films of PEN and C60 showed a reduced HOMO-level offset of 0.85 eV, which increased to 1.45 eV by precoverage of the substrate with a thin PEN layer. In this case, the PEN-HOMO level was Fermi-level pinned at 0.35 eV binding energy and charge transfer between PEN and PEDOT:PSS decreased the vacuum level by 0.75 eV. In addition, the morphology and crystal structure of the respective systems have been investigated by atomic force microscopy (AFM), x-ray diffraction (XRD) and Fourier-transform infrared spectroscopy, which indicated pronounced phase separation of PEN and C60 in the codeposited films. XRD revealed crystalline growth of PEN in all investigated cases forming crystallites that exceeded the nominal film thickness by an order of magnitude, whereas C60 was crystalline only if grown on the PEN precovered substrates. AFM investigations allowed to correlate morphology and structure revealing micro- and nanophase separation between PEN and C60.

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.

Directing phenotype of vascular smooth muscle cells using electrically stimulated conducting polymer

Vascular smooth muscle cells (VSMCs) isolated from rabbit aorta and immortalised A7r5 cells were cultured on conducting polypyrrole (PPy) substrates and were subjected to a 50 μA sinusoidal electrical stimulation at 0.05, 5 and 500 Hz. These substrates were doped with hyaluronic acid and coated with collagen IV followed by Matrigel ® in order to mimic the basement membrane and encourage cell attachment. Increased proliferation and expression of smooth muscle phenotype markers (smooth muscle α-actin and smooth muscle myosin heavy chain) were observed in cultures stimulated at 5 and 500 Hz. This increased proliferation and expression of contractile proteins were found to be significantly decreased when L-type voltage-gated calcium channels (VGCC) were blocked with the drug nifedipine. To the best of our knowledge, this is the first work that demonstrates that VSMCs cultured on a conducting polymer substrate and subject to electrical stimulation not only exhibit enhanced proliferation but can be simultaneously encouraged to increase contractile protein expression. This behaviour is somewhat contrary to the classical definition of smooth muscle contractile and synthetic phenotypes that, in general, requires a modulation in phenotype as a prerequisite for smooth muscle proliferation. This interesting result highlights both the inherent plasticity of vascular smooth muscle cells and the potential of electrical stimulation via conducting polymer substrates to manipulate their behaviour.

Conductive polymer as a controlled microenvironment for the potentiometric high-throughput evaluation of ionic liquid cell toxicity

This paper presents both biological and potentiometric evaluations of the cell toxicity of a widely used ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim]BF(4)), to Chinese hamster lung fibroblast cells (V79 cell line). The innovative potentiometric study takes advantage of the unique properties of conductive polymer polypyrrole (PPY) for the potentiometric evaluation of cell toxicity of [bmim]BF(4) to the V79 cells in a real-time, noninvasive and high-throughput manner. The conductive polymer PPY provides a controlled microenvironment that allows the quantitative release of the anions of the ionic liquids into the cells being monitored in real time and noninvasively. Parallel biological assay results showed that V79 cells exposed to [bmim]BF(4) usually grew in clusters, and that many small vacuoles could be seen in the cytoplasm. At the 24th hour after the V79 cells had been exposed to the ionic liquid (IL), the half inhibition concentration (EC(50)) of [bmim]BF(4) was around 5 mM. From a cell cycle study performed using a FACScan flow cytometer, it was found that the V79 cells could be partially locked to the G(1) phase by [bmim]BF(4), which extended the doubling time for cell growth. Comparing with the EC(50) values of cadmium chloride and mercury chloride, [bmim]BF(4) is not very toxic, but it may have a long-term toxic effect on mammalian cells. Compared to traditional biological in vitro assays, the use of a conductive polymer substrate in combination with a potentiometric sensor array is much more sensitive, faster, and enables a simpler evaluation of chemical cell toxicity. Additionally, it simplifies the study of the reversibility of cell toxicity, i.e., cell recovery, because there is no need to refresh the culture medium since a finite amount of chemicals can be doped and released. We found that the cytotoxicity of [bmim]BF(4) at a concentration of less than 6 mM was reversible for the V79 cell line, because cell morphology and proliferation rate returned to normal after the removal of the IL from the culture medium. This finding suggests that the IL [bmim]BF(4) could be used as a tool to control mammalian cell proliferation rate.

The growth of nickel nanoparticles on conductive polymer composite electrodes

Uniformly sized and dispersed nickel core-shell nanoparticles on polypyrrole have been grown by electrodeposition. Two principal types of Ni particle morphologies were observed: small Ni nanocrystallites ranging in diameter from 7 to 12 nm, and larger spherical Ni clusters of 100 nm to over a micron in size. The type of Ni nanoparticles deposited depends sensitively on the preparation of the conducting polymer substrate. The optimal deposition conditions for the small Ni nanocrystallites were determined. TEM diffraction and XPS analysis show that these nanoparticles are predominantly NiO.

Effects of oxygen gas flow rate and ion beam plasma conditions on the opto-electronic properties of indium molybdenum oxide films fabricated by ion beam-assisted evaporation

The purpose of the present work is to experimentally study the effects of the oxygen gas flow rate and ion beam plasma conditions on the properties of indium molybdenum oxide (IMO) films deposited onto the polyethersulfone (PES) substrate. Crystal structure, surface morphology, and optoelectronic properties of IMO films are examined as a function of oxygen gas flow rate and ion beam discharge voltage. Experimental results show that the IMO films consist of a cubic bixbyite B-In 2O 3 single phase with its crystal preferred orientation alone B(222). Mo 6+ ions are therefore considered to partially substitute In 3+ sites in the deposit. Under-controlled ion bombardment during deposition enhances the reaction among those arriving oxygen and metal ion species to condense into IMO film and facilitates a decreased surface roughness of IMO film. The film with ultimate crystallinity and the lowest surface roughness is obtained when the oxygen flow rate of 3 sccm and the discharge voltage of 110 V are employed. This results in the lowest electrical resistivity due mainly to the increased Hall mobility and irrelevant to carrier concentration. The lowest electrical resistivity of 8.63 × 10 − 4 ohm-cm with a 84.63% transmittance at a wavelength of 550 nm can be obtained, which satisfies the requirement of a flexible transparent conductive polymer substrate.

Electrically Controlled Drug Delivery from Biotin‐Doped Conductive Polypyrrole

A platform for controlled drug delivery using a conductive-polymer substrate has been created. Through the incorporation of biotin into the conductive polymer polypyrrole (PPy) and the subsequent attachment of the desired drug molecule (such as nerve growth factor, NGF) via a streptavidin linker, an applied potential can trigger release of the drug from the polymer surface (see figure).

Opto-electrical processes in a conducting polymer–bacteriorhodopsin system

In this report, we highlight the opto-electrical processes at a conducting polymer–bacteriorhodopsin (bR) interface in presence of a voltage bias. Oriented bR on a conducting polymer substrate forms a unique hybrid system where the oxidation state of the polymer controls the optically activated proton gradient in the bR side. The internal conversion of the intermediate deprotonated M-state and the proton transfer/transport of bR at the interface can be controlled by the electrostatic environment and leads to interesting device features in this process.

Electrochemical preparation and properties of composite films with polypyrrole/poly(styrene sulfonate): polyviologen multilayers

Multilayers consisting of polypyrrole/poly(styrene sulfonate) (PP/PSS) and polyviologen (PV) were electrochemically prepared on Au to enhance long-term and environmental (e.g., pH) stability of PV modified electrodes. PV cationic polyelectrolytes were adsorbed on top of electrochemically synthesized PP/PSS via electrostatic interactions with PSS present at the surface of conducting polymer substrates. By alternating electrochemical synthesis of PP/PSS and PV adsorption in a single medium, multilayers were prepared up to 13 layer-pairs. The electrochemical and electrochromic properties of multilayers produced in this way were quite reproducible, since the film preparation does not require medium changes and the layer thicknesses can be finely controlled using the applied potential and time. Although the redox potential of PP/PSS shifted in the positive direction with increase in the number of layer-pairs, cyclic voltammograms of multilayers indicated that total electroactivity of PP/PSS was retained. PV molecules, sandwiched between reduced PP/PSS layers, were also fully electroactive and quite stable during repeated redox switching processes, indicative of enhanced long-term stability. Multilayers also possessed electrochromic properties which were directly proportional to the number of PV layers.