Bo Zhu

Functionalized Conducting Polymer Nanodots for Enhanced Cell Capturing: The Synergistic Effect of Capture Agents and Nanostructures

Many features of conducting polymers, including simplicity for nanostructure fabrication, tailored functional groups for bioconjugation, intrinsic electrical conductivity, and softer mechanical characteristics than metals, provide advantages as materials for cell-related diagnostic and therapeutic platforms. On the other hand, nanostructured materials have been recently reported with enhanced cell-capturing effi ciency. The enhanced performance are promising for fi nding cells of rare abundance in the blood stream with diagnostic potential, e.g., circulating tumor cells. [ 5–8 ] Here, we report our efforts on the creation of captureagent-functionalized conducting polymer nanodots and their effi cient capture on cells from a synergistic effect combining the ligand and nanostructure. Among all the conducting polymers, we are particularly interested in poly(3,4-ethylenedioxy)thiophenes (PEDOTs) [ 9 , 10 ]

Polydioxythiophene Nanodots, Nonowires, Nano-Networks, and Tubular Structures: The Effect of Functional Groups and Temperature in Template-Free Electropolymerization

Various nanostructures, including nanofibers, nanodots, nanonetwork, and nano- to microsize tubes of functionalized poly(3,4-ethylenedioxythiophene) (EDOT) and poly(3,4-propylenedioxythiophene) (ProDOT) are created by using a template-free electropolymerization method on indium-tin-oxide substrates. By investigating conducting polymer nanostructures containing various functional groups prepared at different polymerization temperature, we conclude a synergistic effect of functional groups and temperature on the formation of polymer nanostructures when a template-free electropolymerization method is applied. For unfunctionalized EDOT and ProDOT, or EDOT containing alkyl functional groups, nanofibers and nanoporous structures are usually found. Interesting, when polar functional groups are attached, conducting polymers tend to form nanodots at room temperature while grow tubular structures at low temperature. The relationship between surface properties and their nanostructures is evaluated by contact angle measurements. The capacity and electrochemical impedance spectroscopy measurements were conducted to understand the electrical properties of using these materials as electrodes. The results provide the relationship between the functional groups, nanostructures, and electrical properties. We also discuss the potential restriction of using this method to create nanostructures. The copolymerization of different functionalized EDOTs may cause irregular and unexpected nanostructures, which indicates the complex interaction between different functionalized monomers during the electropolymerization.

Large enhancement in neurite outgrowth on a cell membrane-mimicking conducting polymer

Although electrically stimulated neurite outgrowth on bioelectronic devices is a promising means of nerve regeneration, immunogenic scar formation can insulate electrodes from targeted cells and tissues, thereby reducing the lifetime of the device. Ideally, an electrode material capable of electrically interfacing with neurons selectively and efficiently would be integrated without being recognized by the immune system and minimize its response. Here we develop a cell membrane-mimicking conducting polymer possessing several attractive features. This polymer displays high resistance towards nonspecific enzyme/cell binding and recognizes targeted cells specifically to allow intimate electrical communication over long periods of time. Its low electrical impedance relays electrical signals efficiently. This material is capable to integrate biochemical and electrical stimulation to promote neural cellular behaviour. Neurite outgrowth is enhanced greatly on this new conducting polymer; in addition, electrically stimulated secretion of proteins from primary Schwann cells can also occur on it.

Controlled Protein Absorption and Cell Adhesion on Polymer-Brush-Grafted Poly(3,4-ethylenedioxythiophene) Films

Tailoring the surface of biometallic implants with protein-resistant polymer brushes represents an efficient approach to improve the biocompability and mechanical compliance with soft human tissues. A general approach utilizing electropolymerization to form initiating group (-Br) containing poly(3,4-ethylenedioxythiophen)s (poly(EDOT)s) is described. After the conducting polymer is deposited, neutral poly((oligo(ethylene glycol) methacrylate), poly(OEGMA), and zwitterionic poly([2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide), poly(SBMA), brushes are grafted by surface-initiated atom transfer radical polymerization. Quartz crystal microbalance (QCM) experiments confirm protein resistance of poly(OEGMA) and poly(SBMA)-grafted poly(EDOT)s. The protein binding properties of the surface are modulated by the density of polymer brushes, which is controlled by the feed content of initiator-containing monomer (EDOT-Br) in the monomer mixture solution for electropolymerization. Furthermore, these polymer-grafted poly(EDOT)s also prevent cells to adhere on the surface.

3D Bioelectronic Interface: Capturing Circulating Tumor Cells onto Conducting Polymer‐Based Micro/Nanorod Arrays with Chemical and Topographical Control

The three-dimensional (3D) poly(3,4-ethylenedioxythiophene) (PEDOT)-based bioelectronic interfaces (BEIs) with diverse dimensional micro/nanorod array structures, varied surface chemical pro-perties, high electrical conductivity, reversible chemical redox switching, and high optical transparency are used for capturing circulating tumor cells (CTCs). Such 3D PEDOT-based BEIs can function as an efficient clinical diagonstic and therapeutic platform.

Oligoethylene-glycol-functionalized polyoxythiophenes for cell engineering: syntheses, characterizations, and cell compatibilities.

A series of methyl- or benzyl-capped oligoethylene glycol functionalized 2,5-dibromo-3-oxythiophenes are synthesized and successfully polymerized by either Grignard metathesis (GRIM) polymerization or reductive coupling polymerization to yield the corresponding polymers in reasonable yields and molecular weights with narrow molecular weight distribution. These synthesized polyoxythiophenes exhibit high electroactivity and stability in aqueous solution when a potential is applied. Polyoxythiophenes from different polymerization approaches display different colors after purification and spectroelectrochemical studies confirm that the difference of color is from the difference of doping state. Little cytotoxicity is observed for the polymers by in vitro cell compatibility assay. NIH3T3 fibroblast cells are well attached and proliferate on spin-coated films. These results indicate that oligoethylene-glycol-functionalized polyoxythiophenes are promising candidates as conducting biomatierals for biomedical and bioengineering applications.

Electropolymerized conjugated polyelectrolytes with tunable work function and hydrophobicity as an anode buffer in organic optoelectronics.

A new class of conductive polyelectrolyte films with tunable work function and hydrophobicity has been developed for the anode buffer layer in organic electronic devices. The work function of these films featuring a copolymer of ethylenedioxythiophene (EDOT), and its functionalized analogues were found to be easily tunable over a range of almost 1 eV and reach values as high as those of PEDOT:PSS. The new buffer material does not need the addition of any insulating or acidic material that might limit the film conductivity or device lifetime. Organic photovoltaic devices built with these films showed improved open-circuit voltage over those of the known PSS-free conductive EDOT-based polymers with values as high as that obtained for PEDOT:PSS. Furthermore, the surface hydrophobicity of these new copolymer films was found to be sensitive to the chemical groups attached to the polymer backbone, offering an attractive method for surface energy tuning.

Nanoscale Analysis of a Functionalized Polythiophene Surface by Adhesion Mapping

Functionalized ethylenedioxythiophene (EDOT) monomers, hydroxymethyl EDOT (EDOT-OH), and zwitterionic phosphorylcholine EDOT (EDOT-PC) were electropolymerized to prepare the homopolymers poly(EDOT-OH) and poly(EDOT-PC), and mixtures of these monomers were used to produce the copolymer poly(EDOT-OH)-co-poly(EDOT-PC). Force-extension-curve-based atomic force microscopy (AFM) was utilized to analyze the surfaces of the films. The PEDOT-OH film yielded force-extension curves for short stretching, and the PEDOT-PC film yielded curves for long stretching. A dendron-modified AFM tip with anthracene groups tethered at the end resulted in adhesion maps with the highest contrast. The analytical data for the copolymer films correlated with the corresponding monomer composition, and the maps revealed that the average size for the copolymer nanodomains ranged from 10-14 nm. This approach can be applied to studies aimed at understanding the surface structure of other relevant polymers and copolymers at the nanoscale level.

Nanoscale analysis of functionalized polythiophene surfaces: the effects of electropolymerization methods and thermal treatment

Functionalized poly(3,4-ethylenedioxythiophene) (PEDOT) thin films fabricated by cyclic voltammetry and potentiostatic electropolymerization were analyzed by adhesion mapping. Two monomers, zwitterionic phosphorylcholine EDOT (EDOT-PC) and hydroxymethyl EDOT (EDOT-OH), were used to prepare the corresponding homopolymers PEDOT-PC and PEDOT-OH. Force–extension curve-based atomic force microscopy (AFM) was used to generate nanoscale-resolution maps revealing the characteristic stretching behavior at each pixel. As expected, the maps for PEDOT-PC consisted mostly of pixels with long stretching curves, whereas the maps for PEDOT-OH consisted of pixels with short stretching curves. The number of pixels with short stretching curves was compared with the number of pixels with long stretching curves. For PEDOT-PC, the relative ratio of the pixels with long stretching increased with the rate of voltage change (or number of cycles) during electropolymerization. The relative ratio of short to long stretched pixels in the film fabricated by potentiostatic electropolymerization was as large as that of the film fabricated by cyclic voltammetry at the highest scan rate (400 mV s−1). The thermal annealing increased the number of pixels with short stretching, indicating that chain reorganization led to stronger interchain adhesion. For PEDOT-OH, the films were composed primarily of pixels with short stretching. The relative short to long stretching ratio was insensitive to the polymerization method. Our approach can be used to resolve the surface structure of polymer films at the nanoscale.

Conducting polymer nanobiointerfaces for biosensing and cell engineering

Conducting polymers are organic polymeric materials which are able to transduce electricity. These materials provide a unique toolkit for studies of biological events through electronic signals, including biosensing and cell engineering. In this research, we create a variety of conducting polymer molecular structures and nanostructures in order to control the biointerfacial properties. The results have demonstrated much improved sensitivity on electrochemical biosenser based on these so-called “conducting polymer nanobiointerfaces” as well as defined cell engineering.