Enhanced differentiation of embryonic and neural stem cells to neuronal fates on laminin peptides doped polypyrrole

PPy is a conducting polymer material that has been widely investigated for biomedical applications. hESCs and adult rNSCs were grown on four PPy surfaces doped with PSS or peptide from laminin (p20, p31, and a mixture of p20 and p31) respectively. After 7 d, both PPy/p20 and PPy/p31 promoted neuroectoderm formation from hESCs. After 14 d of culture, surfaces containing p20 showed the highest percentage of neuronal differentiation from hESC, while the PPy/p31 surface showed better cell attachment and spreading. In rNSCs cultures, a higher percentage of neurons were found on the PPy/p20 surface than other surfaces at 7 and 14 d. For differentiated neurons, p20 promoted both the primary and total neurite outgrowth. Longer primary neurites were found on p20-containing surfaces and a longer total neurite length was found on PPy/p20 surface. These results demonstrated that, by doping PPy with different bioactive peptides, differentiation of stem cells seeded at different stages of development is affected.     

导电聚合物的电化学制备和电化学性质研究——中国科学院有机固体重点实验室导电聚合物电化学研究工作简介(I)

简要介绍本研究组自上世纪80年代以来在导电聚合物的电化学制备和电化学性质研究中取得的一些主要成果,包括吡咯电化学聚合条件的影响、电化学聚合反应机理及其反应动力学、导电聚吡咯的两种掺杂结构及其两步电化学氧化还原过程和电化学过氧化的机理、导电聚苯胺的电化学性质、导电聚合物稳定性的电化学解释等等.     

In situ Raman and UV-vis spectroscopic studies of polypyrrole and poly(pyrrole-2,6-dimethyl-β-cyclodextrin)

Polypyrrole (PPy) and poly(pyrrole-2,6-dimethyl-β-cyclodextrin) [P(Py-β-DMCD)] films prepared by potential cycling in aqueous acidic solutions on indium tin oxide (ITO)-coated glass and gold electrodes were studied by in situ UV-vis and Raman spectroscopy. Characteristic UV-vis and Raman bands were identified and their dependencies on the electrode potential have been discussed. Spectroelectrochemical results reveal differences both in the position of the spectral bands and their potential dependence for PPy and P(Py-β-DMCD) films indicating interactions between polymer chains and CDs during electropolymerization process. The films were also characterized by cyclic voltammetry and FT-IR spectroscopy.     

Growth of aligned polypyrrole acicular nanorods and their application as Pt‐free semitransparent counter electrode in dye‐sensitized solar cell

Polypyrrole films on fluorine doped tin oxide (FTO)‐coated glass substrate were prepared in situ by placing FTO/glass substrates where pyrrole was polymerized by methyl orange‐ferric chloride complex. The atomic force microscopy image indicated growth of acicular nanorods of polypyrrole. These films exhibited catalytic activity towards I₃⁻/I⁻ redox couple and have been investigated for counter electrode application in dye‐sensitized solar cell (DSSC). The fabricated DSSC with N719 dye/TiO₂ as photoanode, and PPy/FTO as counter electrode shows ~1.7% efficiency.     

Design of free‐standing microstructured conducting polymer films for enhanced particle removal from non‐uniform surfaces

Efficient removal of particles from topologically‐complex surfaces is of significant import for a range of applications (e.g., explosive residue removal in security arenas). Here, we synthesize next‐generation polymeric particle removal swabs with tuned structural features to elucidate the influence of the polymer microstructure on the removal of trace particles from surfaces. Specifically, microstructured free‐standing films of the conducting polymer polypyrrole (PPy) were synthesized through template‐assisted electropolymerization techniques. The removal of polystyrene microspheres from representative aluminum surfaces of varying roughness was evaluated as a function of the PPy microstructure. PPy‐based microstructured swabs displayed increased particle trapping properties relative to non‐textured PPy‐based swabs and current commercial swabs. This increased effectiveness occurred from the more intimate particle‐swab contact, leading to increased van der Waals interactions for the microstructured swabs. Therefore, this effort provides critical design rules for the production of microstructured conducting polymer materials for their application toward advanced particle removal technologies. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1968–1974     

Enhancing electrochromic contrast and redox stability of nanostructure polypyrrole film doped by heparin as polyanion in different solvents

Heparin‐doped polypyrrole (PPy‐Hep) and ‐doped polypyrrole (PPy‐ClO₄) films are synthesized onto FTO‐coated glass electrode in a potentiostatic electrochemical process with the aim of producing uniform, transparent, and adherent coating. The resultant polymers are characterized via cyclic voltammetry, scanning electron microscopy (SEM), and UV–vis absorption spectroscopy. SEM study indicates that the PPy‐Hep film to be composed of a continuous interlinked network of quasi spherical grains (50–80 nm in dimensions). The electrochromic properties of PPy‐Hep and PPy‐ClO₄ polymer films are compared to spectroelectrochemistry and switching studies. The effect of different solvents (water, propylene carbonate, and acetonitrile) on the electrochromic features of electropolymerized polymers has been investigated, and we find a very significant solvent effect. PPy‐Hep film exhibits switching time of 1 s and the maximum transmittance contrast (ΔT%) is 48% at 800 nm in water. In addition, presence of Hep causes drastic enhancement of electro‐optical stability of PPy. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3365–3371     

Biofouling of dextran-derivative layers investigated by quartz crystal microbalance

This study reports the fouling of carboxymethyl dextran (CMD) layers in cell culture medium, fibronectin, and serum solutions. CMD layers were covalently immobilized onto amine groups available either on an n-heptylamine plasma polymer (HApp) layer or onto a polyethylenimine (PEI) coating grafted to an acetaldehyde plasma polymer (AApp) layer. The successful immobilization of the graft layers was demonstrated by X-ray photoelectron spectroscopy (XPS). Primary amines on HApp and AApp + PEI surfaces were quantified using a colorimetric assay. Quartz crystal microbalance (QCM) was used to investigate in real-time the fouling of the graft layers upon incubation in cell culture medium (RPMI), fibronectin, and foetal bovine serum (FBS) solutions. HApp, AApp and AApp + PEI layers exhibited large fouling in fibronectin and FBS solutions, while fouling in RPMI cell culture medium was not significant. Protein repellent properties of CMD layers in FBS and fibronectin have been demonstrated compared to the other tested surfaces. QCM has shown that both CMD layers were fouled to a small extent in RPMI medium.     

Polypyrrole thin films formed by admicellar polymerization support the osteogenic differentiation of mesenchymal stem cells

The objective of this study was to evaluate the attachment, proliferation, and differentiation of rat mesenchymal stem cells (MSC) toward the osteoblastic phenotype seeded on polypyrrole (PPy) thin films made by admicellar polymerization. Three different concentrations of pyrrole (Py) monomer (20, 35, and 50 x 10(-3) M) were used with the PPy films deposited on tissue culture polystyrene dishes (TCP). Regular TCP dishes and PPy polymerized on TCP by chemical polymerization without surfactant using 5 x 10(-3) M Py, were used as controls. Rat MSC were seeded on these surfaces and cultured for up to 20 d in osteogenic media. Surface topography was characterized by atomic force microscopy, X-ray photoelectron spectroscopy, and static contact angle. Cell attachment, proliferation, alkaline phosphatase (ALP) activity, and calcium content were measured to evaluate the ability of MSC to adhere and differentiate on PPy-coated TCP. Increased monomer concentrations resulted in PPy films of increased thickness and surface roughness. PPy films generated by different monomer concentrations induced drastically different cellular events. A wide spectrum of cell attachment characteristics (from excellent cell attachment to the complete inability to adhere) were obtained by varying the monomer concentration from 20 m to 50 x 10(-3) M. In particular the 20 x 10(-3) M PPy thin films demonstrated superior induction of MSC osteogenicity, which was comparable to standard TCP dishes, unlike PPy films of similar thickness prepared by chemical polymerization without surfactant. Adhesion of mesenchymal stem cells on tissue culture plates (TCP) coated with polypyrrole thin films made by admicellar polymerization.     

Polypyrrole electrodeposition on inorganic semiconductors CuInSe2 and CuInS2 for photovoltaic applications

Thin polypyrrole (PPy) layers with an average thickness of about 0.5 μm were deposited, using potentiostatic and galvanostatic techniques, on CuInSe₂ (CISe) structures prepared electrochemically on glass/ITO substrates and on CuInS₂ (CIS) structures fabricated on Cu tape substrates. The polymer layer of p-type is considered as an alternative to the traditional buffer layer and window layer in the conventional cell structure. The deposition proceeded from an aqueous solution containing sodium naphthalene-2-sulfonate as a dopant. In order to prepare stable PPy films of high quality with a good adherence to the surface of inorganic semiconductors CIS and CISe, the optimal concentrations of reagents, current densities and electrodepositing potentials were selected experimentally. Electrochemical polymerization of pyrrole to PPy on CIS surfaces is faster under white light irradiation and the polymerisation starts at lower potential than in the dark. Significant photovoltage and photocurrent of the fabricated CISe/PPy and CIS/PPy structures have been observed under standard white light illumination.     

Fabrication and Properties of Conducting Polypyrrole/SWNT‐PABS Composite Films and Nanotubes

We report the electropolymerization and characterization of polypyrrole films doped with poly(m‐aminobenzene sulfonic acid (PABS) functionalized single‐walled nanotubes (SWNT) (PPy/SWNT‐PABS). The negatively charged water‐soluble SWNT‐PABS served as anionic dopant during the electropolymerization to synthesize PPy/SWNT‐PABS composite films. The synthetic, morphological and electrical properties of PPy/SWNT‐PABS films and chloride doped polypyrrole (PPy/Cl) films were compared. Characterization was performed by cyclic voltammetry, atomic force microscopy (AFM), scanning electron microscopy (SEM) and Raman spectroscopy. SEM and AFM images revealed that the incorporation of SWNT‐PABS significantly altered the morphology of the PPy. Cyclic voltammetry showed improved electrochemical properties of PPy/SWNT‐PABS films as compared to PPy/Cl films. Raman Spectroscopy confirmed the presence of SWNT‐PABS within composite films. Field effect transistor (FET) and electrical characterization studies show that the incorporation of the SWNT‐PABS increased the electronic performance of PPy/SWNT‐PABS films when compared to PPy/Cl films. Finally, we fabricated PPy/SWNT‐PABS nanotubes which may lead to potential applications to sensors and other electronic devices.     

Polypyrrole on self-assembled monolayers of a pyrrolyl lipoic acid derivative—electrosynthesis and polymer film characterization

The electropolymerization of pyrrole on gold modified by a self-assembled monolayer (SAM) of a pyrrolyl lipoic acid derivative was investigated in detail and the results compared to those obtained on bare substrates. Both under potentiostatic and potentiodynamic control, a slight blocking action of the underlying SAM could be observed for the initial stages of polymer growth but thereafter the electrochemical features were similar to those collected for polypyrrole (PPy) deposition on bare gold. The morphology and structure of PPy films formed on the SAMs were characterized by atomic force microscopy and X-ray diffraction, which revealed that those polymer properties are much more influenced by the electrochemical mode of preparation, than by the underlying SAMs. While, when compared to PPy on bare gold, no effect has been detected on thin layers deposited at constant potential, surface areas with rather irregular morphology, as well as a small but beneficial influence in inducing order on the first few layers of the polymer film, have been observed on similar films formed by cyclic voltammetry. The typical globular morphology of PPy has always been observed for relatively thick layers in which the redox behavior, analyzed by in situ AFM, showed an increase in volume of the polymer nodules upon reduction, largely due to the SAM reorganization induced by the applied potential.     

Superlow fouling sulfobetaine and carboxybetaine polymers on glass slides

This work describes the superlow fouling properties of glass slides grafted with zwitterionic polymers to highly resist the adsorption of proteins and the adhesion of mammalian cells. Glass slides were first silanized using 2-bromo-2-methyl-N-3-[(triethoxysilyl)propyl]propanamide (BrTMOS). Two zwitterionic polymers, poly(sulfobetaine methacrylate) (polySBMA) and poly(carboxybetaine methacrylate) (polyCBMA), were then grafted from the silanized glass substrates using the atom-transfer radical polymerization (ATRP) method. X-ray photoelectron spectroscopy (XPS) was used to analyze the surfaces of the silanized glass substrates and the substrates grafted with the polymers. An enzyme-linked immonosobrbent assay (ELISA) using polyclonal antibodies was used to measure fibrinogen adsorption on these surfaces. The surfaces with polySBMA or polyCBMA layers were shown to reduce fibrinogen adsorption to a level comparable with that of adsorption on poly(ethylene glycol)-like films. Bovine aortic endothelial cells (BAECs) were seeded on these surfaces. The attachment and spreading of the cells were observed only on unpolymerized glass surfaces. This work further demonstrates that zwitterionic polymers highly resist nonspecific protein adsorption and cell adhesion and provides an effective method to modify glass slides or other oxide surfaces to achieve superlow fouling.     

Development of miniaturized pH biosensors based on electrosynthesized polymer films

A new type of pH biosensor was developed for biological applications. This biosensor was fabricated using silicon microsystem technology and consists in two platinum microelectrodes. The first microelectrode was coated by an electrosynthesized polymer and acted as the pH sensitive electrode when the second one was coated by a silver layer and was used as the reference electrode. Then, this potentiometric pH miniaturized biosensor based on electrosynthesized polypyrrole or electrosynthesized linear polyethylenimine films was tested. The potentiometric responses appeared reversible and linear to pH changes in the range from pH 4 to 9. More, the responses were fast (less than 1 min for all sensors), they were stable in time since PPy/PEI films were stable during more than 30 days, and no interference was observed. The influence of the polymer thickness was also studied.     

Electrochemistry of conductive polymers 39. Contacts between conducting polymers and noble metal nanoparticles studied by current-sensing atomic force microscopy

Electrical properties of contacts formed between conducting polymers and noble metal nanoparticles have been examined using current-sensing atomic force microscopy (CS-AFM). Contacts formed between electrochemically prepared pi-conjugated polymer films such as polypyrrole (PPy), poly(3-methylthiophene) (P3MeT), as well as poly(3,4-ethylenedioxythiophene) (PEDOT) and noble metal nanoparticles including platinum (Pt), gold (Au), and silver (Ag) have been examined. The Pt nanoparticles were electrochemically deposited on a pre-coated PPy film surface by reducing a platinum precursor (PtCl62-) at a constant potential. Both current and scanning electron microscopic images of the film showed the presence of Pt islands. The Au and Ag nanoparticles were dispersed on the P3MeT and PEDOT film surfaces simply by dipping the polymer films into colloid solutions containing Au or Ag particles for specified periods (5 to approximately 10 min). The deposition of Au or Ag particles resulted from either their physical adsorption or chemical bonding between particles and the polymer surface depending on the polymer. When compared with PPy, P3MeT and PEDOT showed a stronger binding to Au or Ag nanoparticles when dipped in their colloidal solutions for the same period. This indicates that Au and Ag particles are predominantly linked with the sulfur atoms via chemical bonding. Of the two, PEDOT was more conductive at the sites where the particles are connected to the polymer. It appears that PEDOT has better aligned sulfur atoms on the surface and is strongly bonded to Au and Ag nanoparticles due to their strong affinity to gold and silver. The current-voltage curves obtained at the metal islands demonstrate that the contacts between these metal islands and polymers are ohmic.     

Patterning on nonplanar substrates: flexible honeycomb films from a range of self-assembling star copolymers

The effect of glass transition temperature, Tg, on the self-assembly of "honeycomb" microstructures on nonplanar substrates was probed by the synthesis of a library of core cross-linked star polymers with different arm compositions. Star polymers based on poly(dimethyl siloxane), poly(ethyl acrylate), poly(methyl acrylate), poly(tert-butyl acrylate), and poly(methyl methacrylate) were synthesized by the "arm first" strategy using atom-transfer radical polymerization. Reaction conditions were optimized, and a series of high molecular weight star polymers were prepared in high yield. The glass transition temperature of the star polymers ranged from -123 to 100 degrees C which allowed the suitability for the formation of porous honeycomb-like films via the "breath figure" technique on nonplanar surfaces to be investigated. All star compositions successfully formed ordered films on flat surfaces. However, only star polymer compositions with a Tg below 48 degrees C could form homogeneous honeycomb coatings on the surface of nonplanar substrates.     

Electrochemical supercapacitive properties of polypyrrole thin films: influence of the electropolymerization methods

A detailed study of the effects of different electropolymerization methods on the supercapacitive properties of polypyrrole (PPy) thin films deposited on carbon cloth is reported. Deposition mechanisms of PPy thin films through cyclic voltammetry (CV), potentiostatic (PS), and galvanostatic (GS) modes have been analyzed. The resulting PPy thin films have been characterized by X-ray photoelectron spectroscopy (XPS), SEM, and TEM. The electrochemical properties of PPy thin films were investigated by cyclic voltammetry and galvanostatic charge/discharge. The results showed that the different electrodeposition modes of synthesis significantly affect the supercapacitive properties of PPy thin films. Among different modes of electrodeposition, PPy synthesized by a potentiostatic mode exhibits maximum specific capacitance of 166 F/g with specific energy of 13 Wh/kg; this is attributed to equivalent proportions of the oxidized and neutral states of PPy. Thus, these results provide a useful orientation for the use of optimized electrodeposition modes for the growth of PPy thin films to be applied as electrode material in supercapacitors.     

ITO pattern fabrication of glass platforms for electropolymerization of light sensitive polymer for its conjugation to bioreceptors on a micro-array

We present herein an effective and versatile method to fabricate a micro-patterned structure of conductive polymer, poly(pyrrole-benzophenone), on Indium Tin Oxide (ITO) glass chips for the subsequent photo-immobilization of various bioreceptor, antigens. Such methodologies are based on photolithography of ITO pattern fabrication on non-conductive surfaces, glass slides, and on a photo-active electrogenerated polymer films. The photo-active polymer serves as a substrate platform for the photo-immobilization of the bioreceptor reagents used for subsequent immunoreactions. We were able to show the resolution of electropolymerization on an ITO pattern as well as immobilization of more than one bioreceptor for the simultaneous detection of several analytes. The antigen micro-arrays were tested for sensitivity, specificity, and overall practicality for the simultaneous detection of analyte anti-Cholera Toxin B, anti-Hepatitis B virus surface and core protein antibodies. In addition we used our pattern ITO-poly(pyrrole-benzophenone) micro-array for the detection of serum samples of Hepatitis B virus patients previously screened by a standard hospital detection method.     

Highly conformal growth of microstructured polypyrrole films by electrosynthesis on micromachined silicon substrates

A novel technology for fabricating microstructured polypyrrole (PPy) films is presented based on PPy electrosynthesis on micromachined silicon substrates. PPy light-activated electropolymerization is performed on n-type microstructured silicon featuring lattices of square-like pores with pitch of 8 μm, size (s) of 5 μm, and depth (d) from 5 μm up to 50 μm. Scanning electron microscopy (SEM) highlights as light-activation allows a highly conformal polymer growth yielding a three-dimensional PPy structure perfectly replicating the silicon microstructure to be achieved up to high aspect-ratio (HR = d/s). Arrays of highly ordered PPy hollow microtubes with depth up to 50 μm and thickness up to 1 μm are obtained. Chemical analysis of microstructured PPy films is performed by X-ray photoelectron spectroscopy (XPS) and their electrochemical activity is verified by cyclic voltammetry (CV).     

ELECTROACTIVE AND NANOSTRUCTURED POLYMERS AS SCAFFOLD MATERIALS FOR NEURONAL AND CARDIAC TISSUE ENGINEERING

Conducting polymer, polyaniline （PANI）, has been studied as a novel electroactive and electrically conductive material for tissue engineering applications. The biocompatibility of the conductive polymer can be improved by （i） covalently grafting various adhesive peptides onto the surface of prefabricated conducting polymer films or into the polymer structures during the synthesis, （ii） co-electrospinning or blending with natural proteins to form conducting nanofibers or films, and （iii） preparing conducting polymers using biopolymers, such as collagen, as templates. In this paper, we mainly describe and review the approaches of covalently attaching oligopeptides to PANI and electrospinning PANI-gelatin blend nanofibers. The employment of such modified conducting polymers as substrates for enhanced cell attachment, proliferation and differentiation has been investigated with neuronal PC-12 cells and H9c2 cardiac myoblasts. For the electrospun PANI- gelatin fibers, depending on the concentrations of PANI, H9c2 cells initially displayed different morphologies on the fibrous substrates, but after one week all cultures reached confluence of similar densities and morphologies. Furthermore, we observed, that conductive PANI, when maintained in an aqueous physiologic environment, retained a significant level of electrical conductivity for at least 100 h, even though this conductivity was decreasing over time. Preliminary data show that the application of micro-current stimulates the differentiation of PC-12 cells. All the results demonstrate the potential for using PANI as an electroactive polymer in the culture of excitable cells and open the possibility of using this material as an electroactive scaffold for cardiac and/or neuronal tissue engineering applications that require biocompatibility of conductive polymers.     

Perchlorate interchange during the redox process of PPy/PVS films in an acetonitrile medium. a voltammetric and EDX study

Polypyrrole/poly(vinyl sulfonate) (PPy/PVS) films in acetonitrile containing 0.1 M LiClO4 were studied by cyclic voltammetry. Consecutive voltammograms pointed to a continuous increase in the charge involved in the process, suggesting a rise in the number of the electroactive participants involved in the redox process. However, voltammograms obtained for the PPy/ClO4 films in analogous conditions pointed to a steady-state behavior from the very early cycles. Theoretical studies based on the Nernst and Butler-Volmer equations indicated that perchlorate ions are involved during the oxidation/reduction process of the PPy/PVS films when the steady state is reached. This result was confirmed by "ex situ" energy-dispersive X-ray analysis of the films. In this regard, the electrochemical behavior of PPy/PVS polymers was similar to that of PPy/ClO4 films when a high number of cycles were carried out. The exchange of ClO4- during the redox reaction of the PPy/PVS films made it necessary to incorporate Li+ cations inside the polymer during the initial voltammetric cycles to compensate for the negative charges of PVS polyanions. Li+ cations are mainly stabilized inside the polymer by the ion pairs formed with the sulfonated groups of the PVS. An increase and shift of the voltammetric cycles indicated a restructuring of the polymeric chains with consecutive scans.