Jungmok You

Solution processable and patternable poly(3,4-alkylenedioxythiophene)s for large-area electrochromic films.

Interest in electrochromic π -conjugated polymers (ECPs) has recently increased considerably for their tunability of colors, low cost of preparation, and low-voltage operation. [ 1–11 ] Among the ECPs, polymers from heterocyclic monomers containing pyrrole, [ 12 ] thiophene, [ 13 ] and selenophene [ 14–16 ] derivatives have been applied to electrochromic devices for simple fi lm processing and high electrochromic contrast. In particular, recent advances in the synthesis of poly(3,4-alkylenedioxythiophene)s (PXDOTs) and their derivatives have offered new opportunities for low energy consumption and electrochemically stable transmissive/absorptive electrochromic devices (ECDs) with fast switching times and full color. [ 17–21 ]

Conductive polymers for next-generation energy storage systems: recent progress and new functions

Conductive polymers are attractive organic materials for future high-throughput energy storage applications due to their controllable resistance over a wide range, cost-effectiveness, high conductivity (>103 S cm−1), light weight, flexibility, and excellent electrochemical properties. In particular, conductive polymers can be directly incorporated into energy storage active materials, which are essential for building advanced energy storage systems (ESSs) (i.e. supercapacitors and rechargeable batteries). This review summarizes the synthesis of conductive polymers with different chemical structures in various ways and also addresses their widespread applications for a broader range of ESSs. Moreover, we introduce recent progress in ESS development, including new electroactive polymers, new approaches (i.e. flexible, stretchable, binder-free, hybrid, etc.), and new functions (e.g. color changeable electrochromic materials for displays).

Electrochemical Fluorescence Switching from a Patternable Poly(1,3,4‐oxadiazole) Thin Film

A highly soluble poly(1,3,4-oxadiazole) (POD) substituted with long alkyl chains was examined for electrochemical fluorescence switching. The high solubility of the polymers enabled a simple fabrication of an electrochemical cell, which showed reversible fluorescence switching between dark (n-doping) and bright (neutral) states with a maximum on/off ratio of 2.5 and a cyclability longer than 1000 cycles. Photochemical cleavage of the oxadiazole in POD allowed photo-patterning of the POD film upon exposure to UV source. The patterned POD films displayed patterned image reversibly under a step potential of +1.8/-1.8 V.

Neural transdifferentiation of human bone marrow mesenchymal stem cells on hydrophobic polymer-modified surface and therapeutic effects in an animal model of ischemic stroke.

Human bone marrow-derived mesenchymal stem cells (MSCs) have multi-lineage differentiation potential and can become cells of mesodermal and neural lineages. These stem cells thus hold considerable clinical promise for the treatment of neurodegenerative diseases. For successful regeneration of damaged neural tissues, directed differentiation of neural or neuronal precursor cells from MSCs and integration of transplanted cells are pivotal factors. We induced MSCs into neurogenesis using a modified protocol. The therapeutic potency of the resulting neural progenitor cells in a rat model of ischemic stroke was analyzed. Using a highly hydrophobic diphenylamino-s-triazine-bridged p-phenylene (DTOPV)-coated surface and adopting a procedure for propagation of neural stem cells, we efficiently converted MSCs into neurosphere-like cellular aggregates (NS-MSCs). The spherical cells were subsequently induced to differentiate into neural cells expressing neuroectodermal markers. To determine whether these cells had neuronal fates and induced neuro-protective effects in vivo, NS-MSCs were intra-cerebrally administered to rats 48h after permanent middle cerebral artery occlusion (pMCAo). The results showed a remarkable attenuation of ischemic damage with significant functional recovery, although the cells were not fully incorporated into the damaged tissues on post-operative day 26. Improvement in the NS-MSC-transplanted rats was faster than in the MSC group and suppression of inflammation was likely the key factor. Thus, our culture system using the hydrophobic surface of a biocompatible DTOPV coating efficiently supported neural cell differentiation from MSCs. Neural-primed MSCs exhibited stronger therapeutic effects than MSCs in rat brains with pMCAo.

Noninvasive photodetachment of stem cells on tunable conductive polymer nano thin films: selective harvesting and preserved differentiation capacity.

Viable mesenchymal stem cells (MSCs) were efficiently and selectively harvested by near-infrared (NIR) light using the photothermal effect of a conductive polymer nano thin film. The poly(3,4-ethylenedioxy thiophene) (PEDOT)-coated cell culture surfaces were prepared via a simple and fast solution-casting polymerization (SCP) technique. The absorption of PEDOT thin films in the NIR region was effectively triggered cell harvesting upon exposure to an NIR source. By controlling the NIR absorption of the PEDOT film through electrochemical doping or growing PEDOT with different thin film thickness from 70 to 300 nm, the proliferation and harvesting of MSCs on the PEDOT surface were controlled quantitatively. This light-induced cell detachment method based on PEDOT films provides the temporal and spatial control of cell harvesting, as well as cell patterning. The harvested stem cells were found to be alive and well proliferated despite the use of temperature increase by NIR. More importantly, the harvested MSCs by this method preserved their intrinsic characteristics as well as multilineage differentiation capacities. This PEDOT surfaces could be used for repetitive culture and detachment of MSCs or for efficient selection or depletion of a specific subset from heterogeneous population during culture of various tissue-derived cells because there were no photodegradation and photobreakage in the PEDOT films by NIR exposure.

Electrochemical Fluorescence Switching from Anthracene Polymer Films

Electrochemical fluorescence switching of electroactive fluorescent anthracene polymer films was studied using an electro active quencher. The fluorescence of a methylene anthracene polymer (PMAn) was intact under redox reaction in the absence of an electroactive quencher. Interestingly the fluorescence of a methylene bridged anthracene polymer (PMAn) film could be modulated by adjusting the redox state of the PMAn and redox reaction of the quencher. The electrochemical fluorescence switching from the PMAn film with a quencher was reversible and the cyclability was longer than 1,000 cycles with an ON/OFF ratio of 3.86 under the applied potential step of +2 V for 4 second. A multi state fluorescent switch was fabricated with a double layered two electrode cell that was consisting of the PMAn layer doped with a quencher and a solid polymer electrolyte layer (SPE).

Catalytic Polymerization of Anthracene in a Recyclable SBA‐15 Reactor with High Iron Content by a Friedel–Crafts Alkylation

Ironing it out: A FeSBA-15 catalyst with a high iron content as well as a large pore diameter has been synthesized and used for the production of soluble poly(methylene anthracene) (PMAn, see scheme). The catalyst is stable, active, reusable, and affords a high yield of high-molecular-weight PMAn. The properties of the PMAns obtained can be controlled by tuning the specific surface area, pore diameter, pore volume, and Fe content of the catalysts.

Highly Fluorescent Conjugated Polyelectrolyte for Protein Sensing and Cell-Compatible Chemosensing Applications

Using a highly fluorescent, water-soluble polymer derived from a triazine-bridged copolymer (DTMSPV), we explored the tunable fluorescence properties of the water-soluble DTMSPV by solvent polarity to function as a fluorescence sensory probe for protein sensing. The green-blue fluorescence from DTMSPV was significantly enhanced in the presence of bovine serum albumin through hydrophobic interactions. Meanwhile, complete quenching of the fluorescence from DTMSPV occurred in the presence of hemoglobin through iron complexation with the polyelectrolyte. In addition, the DTMSPVs were highly fluorescent and permeated into living mesenchymal stem cells (MSCs), enabling effective imaging of the MSCs. This permeation into stem cells is crucial to the detection of Al(3+) in living MSCs. The interaction between the triazine units in DTMSPV with the Al(3+) ions allows for the detection of Al(3+) in living cells. Thus, a strong fluorescence from living MSCs pretreated with DTMSPV was quenched as a function of the Al(3+) concentration, confirming that DTMSPV is a cell-permeable fluorescent polymer that can function as a versatile probe to detect Al(3+) in living cells.

A Single-Step Synthesis of Electroactive Mesoporous ProDOT-Silica Structures

The single-step preparation of highly ordered mesoporous silica hybrid nanocomposites with conjugated polymers was explored using a novel cationic 3,4-propylenedioxythiophene (ProDOT) surfactant (PrS). The method does not require high-temperature calcination or a washing procedure. The combination of self-assembly of the silica surfactant and in situ polymerization of the ProDOT tail is responsible for creation of the mesoporosity with ultralarge pores, large pore volume, and electroactivity. As this novel material exhibits excellent textural parameters together with electrical conductivity, we believe that this could find potential applications in various fields. This novel concept of creating mesoporosity without a calcination process is a significant breakthrough in the field of mesoporous materials and the method can be further generalized as a rational preparation of various mesoporous hybrid materials having different structures and pore diameters.

Protein coverage on polymer nanolayers leading to mesenchymal stem cell patterning

Interactions of gelatin and albumin with a photo-reactive diphenylamino-s-triazine bridged p-phenylene vinylene polymer (DTOPV) were examined by using surface plasmon resonance (SPR) spectroscopy to explore the effect of the polymer structure on protein coverage of DTOPV nanofilms. The SPR data revealed a significant increase of gelatin adsorption on UV-DTOPV nanofilms, while the adsorption of albumin was decreased by UV exposure in the time frame of the experiment. We also found that the selective adsorption of these proteins was highly dependent on the protein concentration; the highest selectivity of protein adsorption was obtained at the lowest concentration (3.5 μg ml(-1)), while no selective adsorption was confirmed at high concentrations (350 and 1000 μg ml(-1)). The selective attachment of mesenchymal stem cells (MSCs) was directly correlated with the selective adsorption of these proteins onto DTOPV nanofilms. The MSCs attachment onto UV-DTOPV films was promoted with only small mass coverage of gelatin, which led to MSC patterning onto the patterned DTOPV nanofilms successfully. The role of cell adhesion proteins that we found in this study will be a clue to elucidate the complex response of biomolecules on functional polymer nanolayers, and contribute to build up biocompatible surfaces on various advanced materials for the sake of cell engineering and medical implants.