Flexible Conductive Polymer Patterns from Vapor Polymerizable and Photo-Cross-Linkable EDOT

We explored direct photopatterning of a vapor polymerizable and photo-cross-linkable 3,4-ethylenedioxythiopene (EDOT) to make it suitable for use in electronics applications. We prepared a conductive polymer, PEDOT-MA, using vapor phase polymerization (VPP) of the (2,3-dihydrothieno[3,4-b][1,4]dioxin-2-yl)methyl methacrylate (EDOT-MA) and photochemically induced a conductivity change of the PEDOT-MA film to ensure a flexible conductive pattern. The room-temperature conductivity (σRT) of the PEDOT-MA film on PET was 30−120 S/cm, depending on the oxidant layer thickness and was increased ∼30% when the PEDOT-MA film was doped with aqueous solution of p-toluenesulfonic acid. Photoreaction of PEDOT-MA decreased the σRT to 1.7 × 10−3 S/cm because of the photo-cross-linking of the side chain. The transparency of the conductive films was tuned using the vapor polymerization time to control the film thickness. The photo-cross-linking reaction of the side chain generated micropatterns having line widths of 50−0.9 μm, in which the light-exposed areas appeared as bleached and less conductive. A diffractive, flexible, conductive film with 41% of diffraction efficiency was obtained from the line-patterned film having a spacing of 0.9 μm

Hybrid Nanoarchitectonics with Conductive Polymer-Coated Regenerated Cellulose Fibers for Green Electronics

Green electronics based on biodegradable polymers have received considerable attention as a solution to electronic waste (e-waste). Herein, we describe an efficient approach to constructing green conductive fibers, comprising poly(3,4-ethylenedioxythiophene) (PEDOT) and regenerated cellulose (RC), via a wet-spinning process and vapor-phase polymerization (VPP). Eco-friendly RC fibers were prepared as a support layer by wet spinning, and the conductive PEDOT layers were coated onto the surface of the RC fibers by the oxidation of EDOT monomers. We demonstrated that the vapor-phase-polymerized PEDOT/RC composite fibers (PEDOT/RC-VPP) exhibited approximately 17 times higher electrical conductivity (198.2 ± 7.3 S/cm), compared with that of the solution-phase-polymerized PEDOT/RC composite fibers (PEDOT/RC-SPP, 11.6 ± 0.6 S/cm). Importantly, PEDOT/RC-VPP exhibited a high tensile strength of 181 MPa, good flexibility, and long-standing electrical stability under ambient air conditions. Moreover, the obtained PEDOT/RC-VPP under 50% strain turned on a green light-emitting diode (LED), indicating the flexibility and stability of green conductive fibers. This strategy can be easily integrated into various electronic textiles for the development of next-generation wearable green electronics

A Simple Silver Nanowire Patterning Method Based on Poly(Ethylene Glycol) Photolithography and Its Application for Soft Electronics

Hydrogel-based flexible microelectrodes have garnered considerable attention recently for soft bioelectronic applications. We constructed silver nanowire (AgNW) micropatterns on various substrates, via a simple, cost-effective, and eco-friendly method without aggressive etching or lift-off processes. Polyethylene glycol (PEG) photolithography was employed to construct AgNW patterns with various shapes and sizes on the glass substrate. Based on a second hydrogel gelation process, AgNW patterns on glass substrate were directly transferred to the synthetic/natural hydrogel substrates. The resultant AgNW micropatterns on the hydrogel exhibited high conductivity (ca. 8.40 x 103 S cm-1) with low sheet resistance (7.51 ± 1.11¿/sq), excellent bending durability (increases in resistance of only ¿3 and ¿13% after 40 and 160 bending cycles, respectively), and good stability in wet conditions (an increase in resistance of only ¿6% after 4 h). Considering both biocompatibility of hydrogel and high conductivity of AgNWs, we anticipate that the AgNW micropatterned hydrogels described here will be particularly valuable as highly efficient and mechanically stable microelectrodes for the development of next-generation bioelectronic devices, especially for implantable biomedical devices

Excimer Emission from Self-Assembly of Fluorescent Diblock Copolymer Prepared by Atom Transfer Radical Polymerization

Well-defined fluorescent copolymers of methyl methacrylate with 1-pyreneylmethyl methacrylate were synthesized by atom transfer radical polymerization (ATRP). The random and block copolymer could be clearly distinguished by their glass-transition temperature (Tg) values, with a single Tg value (124 °C) for the random polymer, and two Tg values (115 and 158 °C) for the block copolymer. The emission spectra of the copolymers were different in excimer emission, allowing analysis of the ordering of the two polymers, by determining the ratio between excimer emission (IE) and monomer emission (IM). The fluorescence spectra of the random copolymer exhibited both monomer and excimer emission of pyrene with a IE/IM ratio of 1.20−1.39 at a concentration of 0.001−0.05 mg/mL. The block copolymer exhibited strong excimer emission with an emission quantum yield for the excimer (ΦE) of 42%. The IE/IM ratio from the block copolymer was >25, even in a very dilute solution. The ΦE value increased to 68% when the block copolymer solution was processed to a thin film, indicating increased interactions among the pyrene block by self-assembly. In addition, nanopores were formed from the block copolymer, while no specific morphology was found from the random copolymer. The average diameter of the nanopores from block copolymer was ∼300 nm. Upon thermal annealing of the block copolymer film, a dramatic increase in excimer emission was observed to give a high ΦE value of 89%. A face-to-face pyrene assembly in the block copolymer was observed on the high-resolution transmission electron microscopy (HR-TEM) images, from which the average packing period of the well-defined pyrene block was estimated to range from 4.5 Å for pyrene block width to 5.6 Å for the width of PMMA mainchain

2,2,6,6-Tetramethylpiperidine-1-oxy-Oxidized Cellulose Nanofiber-Based Nanocomposite Papers for Facile In Situ Surface-Enhanced Raman Scattering Detection

In this study, we report a flexible transparent freestanding surface-enhanced Raman scattering (SERS) platform composed of 2,2,6,6-tetramethylpiperidine-1-oxy-oxidized cellulose nanofibers (TEMPO-CNF) and gold nanoparticles (AuNPs) such as nanospheres (AuNSs) and nanorods (AuNRs) for in situ chemical sensing of a real-world surface. The TEMPO-CNF/AuNP-based nanocomposites were fabricated using two-step filtration with a pure TEMPO-CNF solution and a TEMPO-CNF/AuNP mixture solution. We demonstrate that the TEMPO-CNF/AuNR nanocomposite reveals better SERS activity than the TEMPO-CNF/AuNS nanocomposite. The TEMPO-CNF/AuNR nanocomposite detected rhodamine 6G down to 10 nM with a high enhancement factor of 2.1 × 107 and exhibited good SERS measurement reproducibility in the flexible/bent state. No significant change in SERS intensity was observed even after 1000 cycles of bending to nearly 90°. Importantly, the flexible transparent TEMPO-CNF matrix allows the TEMPO-CNF/AuNR nanocomposite to be tightly wrapped onto the surface of an agricultural product for in situ detection as well as to directly detect pesticide residues down to 60 ng/cm2, which is much lower than the maximum residue level for food safety. This high-performance SERS substrate based on a flexible transparent nanopaper for rapid in situ detection has great potential in various practical applications such as food safety and environmental monitoring

A Fluorescent Polymer for Patterning of Mesenchymal Stem Cells

UV exposure of a fluorescent polymer, diphenylamino-s-triazine bridged p-phenylene vinylene polymer (DTOPV), resulted in fluorescence quenching and a change in surface wettability via photo-oxidation. Patterned polymer films were prepared simply by exposing the polymer film to UV source through a photomask under air. The UV-exposed region was highly biocompatible and provided selective mesenchymal stem cells (MSCs) attachment on it. This allowed cell alignment and patterning along the line patterns of linear, curved, and even various letter shapes. The proliferation rate of MSCs cultured on UV exposed surface (DTOPV+UV) was higher than that of the unexposed surface, and the cells were increased to10-fold after 6 days. The attachment of MSCs was highly selective to the UV-exposed pattern in the presence of collagen and gelatin, which induced cell patterning and attachment through hydrophilic interaction with the UV exposed area. Taking advantage of the emission from the DTOPV pattern, the cell location and pattern images were easily detected through a microscope with or without an excitation probe beam. These studies provide an exciting opportunity for novel cell patterning by a simple photopatterning process using a highly fluorescent DTOPV

Label-Free Surface-Enhanced Raman Scattering Detection of Fire Blight Pathogen Using a Pathogen-Specific Bacteriophage

Fire blight is one of the most devastating plant diseases, causing severe social and economic problems. Herein, we report a novel method based on label-free surface-enhanced Raman scattering (SERS) combined with an Erwinia amylovora-specific bacteriophage that allows detecting efficiently fire blight bacteria E. amylovora for the first time. To achieve the highest SERS signals for E. amylovora, we synthesized and compared plasmonic nanoparticles (PNPs) with different sizes, i.e., bimetallic gold core–silver shell nanoparticles (Au@AgNPs) and monometallic gold nanoparticles (AuNPs) and utilized the coffee-ring effect for the self-assembly of PNPs and enrichment of fire blight bacteria. Furthermore, we investigated the changes in the SERS spectra of E. amylovora after incubation with an E. amylovora-specific bacteriophage, and we found considerable differences in the SERS signals as a function of the bacteriophage incubation time. The results indicate that our bacteriophage-based label-free SERS analysis can specifically detect E. amylovora without the need for peak assignment on the SERS spectra but simply by monitoring the changes in the SERS signals over time. Therefore, our facile method holds great potential for the label-free detection of pathogenic bacteria and the investigation of viral–bacterial interactions

Hollow Microspherical and Microtubular [3 + 3] Carbazole-Based Covalent Organic Frameworks and Their Gas and Energy Storage Applications

Covalent organic frameworks (COFs) are a family of crystalline porous networks having applications in various fields, including gas and energy storage. Despite respectable progress in the synthesis of such crystalline materials, examples of the use of template-free methods to construct COFs having hollow nano- and microstructures are rare. Furthermore, all reported methods for synthesizing these hollow structural COFs have involved [4 + 2] and [3 + 2] condensations. Herein, we report the synthesis of hollow microspherical and microtubular carbazole-based COFs through template-free, one-pot, [3 + 3] condensations of the novel triamine 9-(4-aminophenyl)-carbazole-3,6-diamine (Car-3NH2) and triformyl linkers with various degrees of planarity. Depending upon the monomer’s planarity, a unique morphological variety was observed. A time-dependent study revealed that each COF formed through an individual mechanism depended on the degree of planarity of the triformyl linker; it also confirmed that the hollow structures of these COFs formed through inside-out Ostwald ripening. Our COFs exhibited high Brunauer–Emmett–Teller surface areas (up to ca. 1400 m2 g–1), excellent crystallinity, and high thermal stability. Moreover, the CO2 uptake capacities of these COFs were excellent: up to 61 and 123 mg g–1 at 298 and 273 K, respectively. The high surface areas facilitated greater numbers of strong interactions with CO2 molecules, leading to high CO2 uptake capacities. Moreover, the prepared COFs exhibited redox activity because of their redox-active triphenylamine and pyridine groups, which can be utilized in electrochemical energy storages. Accordingly, such hollow COFs having high surface areas appear to be useful materials for industrial and biological applications

Impact of Nanotopography, Heparin Hydrogel Microstructures, and Encapsulated Fibroblasts on Phenotype of Primary Hepatocytes

Hepatocytes, the main epithelial cell type in the liver, perform most of the biochemical functions of the liver. Thus, maintenance of a primary hepatocyte phenotype is crucial for investigations of in vitro drug metabolism, toxicity, and development of bioartificial liver constructs. Here, we report the impact of topographic cues alone and in combination with soluble signals provided by encapsulated feeder cells on maintenance of the primary hepatocyte phenotype. Topographic features were 300 nm deep with pitches of either 400, 1400, or 4000 nm. Hepatocyte cell attachment, morphology and function were markedly better on 400 nm pitch patterns compared with larger scale topographies or planar substrates. Interestingly, topographic features having biomimetic size scale dramatically increased cell adhesion whether or not substrates had been precoated with collagen I. Albumin production in primary hepatocytes cultured on 400 nm pitch substrates without collagen I was maintained over 10 days and was considerably higher compared to albumin synthesis on collagen-coated flat substrates. In order to investigate the potential interaction of soluble cytoactive factors supplied by feeder cells with topographic cues in determining cell phenotype, bioactive heparin-containing hydrogel microstructures were molded (100 μm spacing, 100 μm width) over the surface of the topographically patterned substrates. These hydrogel microstructures either carried encapsulated fibroblasts or were free of cells. Hepatocytes cultured on nanopatterned substrates next to fibroblast carrying hydrogel microstructures were significantly more functional than hepatocytes cultured on nanopatterned surfaces without hydrogels or stromal cells significantly elevated albumin expression and cell junction formation compared to cells provided with topographic cues only. The simultaneous presentation of topographic biomechanical cues along with soluble signaling molecules provided by encapsulated fibroblasts cells resulted in optimal functionality of cultured hepatocytes. The provision of both topographic and soluble signaling cues could enhance our ability to create liver surrogates and inform the development of engineered liver constructs