Showing papers by "Jin Young Oh published in 2017"
TL;DR: The increased polymer chain dynamics under nanoconfinement significantly reduces the modulus of the conjugated polymer and largely delays the onset of crack formation under strain, and the fabricated semiconducting film can be stretched up to 100% strain without affecting mobility, retaining values comparable to that of amorphous silicon.
Abstract: Soft and conformable wearable electronics require stretchable semiconductors, but existing ones typically sacrifice charge transport mobility to achieve stretchability. We explore a concept based on the nanoconfinement of polymers to substantially improve the stretchability of polymer semiconductors, without affecting charge transport mobility. The increased polymer chain dynamics under nanoconfinement significantly reduces the modulus of the conjugated polymer and largely delays the onset of crack formation under strain. As a result, our fabricated semiconducting film can be stretched up to 100% strain without affecting mobility, retaining values comparable to that of amorphous silicon. The fully stretchable transistors exhibit high biaxial stretchability with minimal change in on current even when poked with a sharp object. We demonstrate a skinlike finger-wearable driver for a light-emitting diode.
796 citations
TL;DR: In this article, a bifunctional separator of 1T exfoliated MoS2@CNT in a tandem configuration (layer-by-layer structure)-coated Celgard rather than a hetero-configuration was presented.
Abstract: Lithium-sulfur (Li-S) batteries are experiencing a design shift from a closed structure to an open structure to further improve their performance, expanding the design realm from the development of nanostructured materials for the cathode to the production of functional separators. Rational guidelines for preparing a bifunctional separator with exfoliated MoS2 and CNTs are suggested to deal with two conflicting issues: guaranteeing the electron pathway while strongly trapping polysulfide species. In addition, various exfoliation methods ranging from mechanical to chemical were investigated to identify an adequate method for preparing exfoliated MoS2 based-bifunctional separators. The electrochemical exfoliation method was found to be effective in not only exfoliating high quality MoS2 in terms of the lateral size and number of layers, but also providing a favorable MoS2 phase, 1T metallic MoS2. A bifunctional separator of 1T exfoliated MoS2@CNT in a tandem configuration (layer-by-layer structure)-coated Celgard rather than a hetero-configuration delivered an excellent electrochemical performance of ∼670 mA h g−1 after 500 cycles at a high current density of 1C. In addition, the separator was highly effective in trapping polysulfide species and facilitating electron transfer to the irreversible discharge products. The rational guidelines suggested in this study will be extended to other two-dimensional transition-metal dichalcogenides, and applied to the development of other functional membranes.
112 citations
TL;DR: Intrinsically stretchable transistors composed of single-walled carbon nanotube (SWNT) electrodes and semiconductors and a dielectric that consists of a nonpolar elastomer enabled hysteresis-free device characteristics.
Abstract: Stretchable form factors enable electronic devices to conform to irregular 3D structures, including soft and moving entities. Intrinsically stretchable devices have potential advantages of high surface coverage of active devices, improved durability, and reduced processing costs. This work describes intrinsically stretchable transistors composed of single-walled carbon nanotube (SWNT) electrodes and semiconductors and a dielectric that consists of a nonpolar elastomer. The use of a nonpolar elastomer dielectric enabled hysteresis-free device characteristics. Compared to devices on SiO2 dielectrics, stretchable devices with nonpolar dielectrics showed lower mobility in ambient conditions because of the absence of doping from water. The effect of a SWNT band gap on device characteristics was investigated by using different SWNT sources as the semiconductor. Large-band-gap SWNTs exhibited trap-limited behavior caused by the low capacitance of the dielectric. In contrast, high-current devices based on SWNTs w...
56 citations
TL;DR: The photoactive nanoweb substrates developed in this study may serve as platforms for producing stem cell therapeutics with enhanced neurogenesis and neuromodulation via optoelectrical control of stem cells.
Abstract: Optoelectrical manipulation has recently gained attention for cellular engineering; however, few material platforms can be used to efficiently regulate stem cell behaviors via optoelectrical stimulation. In this study, we developed nanoweb substrates composed of photoactive polymer poly(3-hexylthiophene) (P3HT) to enhance the neurogenesis of human fetal neural stem cells (hfNSCs) through photo-induced electrical stimulation. Methods The photoactive nanoweb substrates were fabricated by self-assembled one-dimensional (1D) P3HT nanostructures (nanofibrils and nanorods). The hfNSCs cultured on the P3HT nanoweb substrates were optically stimulated with a green light (539 nm) and then differentiation of hfNSCs on the substrates with light stimulation was examined. The utility of the nanoweb substrates for optogenetic application was tested with photo-responsive hfNSCs engineered by polymer nanoparticle-mediated transfection of an engineered chimeric opsin variant (C1V1)-encoding gene. Results The nanoweb substrates provided not only topographical stimulation for activating focal adhesion signaling of hfNSCs, but also generated optoelectrical stimulation via photochemical and charge-transfer reactions upon exposure to 539 nm wavelength light, leading to significantly enhanced neuronal differentiation of hfNSCs. The optoelectrically stimulated hfNSCs exhibited mature neuronal phenotypes with highly extended neurite formation and functional neuron-like electrophysiological features of sodium currents and action potentials. Optoelectrical stimulation with 539 nm light simultaneously activated both C1V1-modified hfNSCs and nanoweb substrates, which upregulated the expression and activation of voltage-gated ion channels in hfNSCs and further increased the effect of photoactive substrates on neuronal differentiation of hfNSCs. Conclusion The photoactive nanoweb substrates developed in this study may serve as platforms for producing stem cell therapeutics with enhanced neurogenesis and neuromodulation via optoelectrical control of stem cells.
30 citations
TL;DR: The feasibility of using solar cell ES derived from a wearable solar cell for inducing angiogenesis in ischemic tissue is shown, showing higher angiogenic efficacy than conventional MSC therapy.
Abstract: Cell therapy has been suggested as a treatment modality for ischemic diseases, but the poor survival and engraftment of implanted cells limit its therapeutic efficacy. To overcome such limitation, we used electrical stimulation (ES) derived from a wearable solar cell for inducing angiogenesis in ischemic tissue. ES enhanced the secretion of angiogenic growth factors and the migration of mesenchymal stem cells (MSCs), myoblasts, endothelial progenitor cells, and endothelial cells in vitro. In a mouse ischemic hindlimb model, ES generated by a solar cell and applied to the ischemic region promoted migration of MSCs toward the ischemic site and upregulated expression of angiogenic paracrine factors (vascular endothelial, basic fibroblast, and hepatocyte growth factors; and stromal cell-derived factor-1α). Importantly, solar cell-generated ES promoted the formation of capillaries and arterioles at the ischemic region, attenuated muscle necrosis and fibrosis, and eventually prevented loss of the ischemic limb....
23 citations