Doo Hyun Yoon

Functional recovery after human umbilical cord blood cells transplantation with brain-derived neutrophic factor into the spinal cord injured rat

SummaryThere have been many efforts to recover neuronal function from spinal cord injuries, but there are some limitations in the treatment of spinal cord injuries.The neural stem cell has been noted for its pluripotency to differentiate into various neural cell types. The human umbilical cord blood cells (HUCBs) are more pluripotent and genetically flexible than bone marrow neural stem cells. The HUCBs could be more frequently used for spinal cord injury treatment in the future.Moderate degree spinal cord injured rats were classified into 3 subgroups, group A: media was injected into the cord injury site, group B: HUCBs were transplanted into the cord injury site, and group C: HUCBs with BDNF (Brain-derived neutrophic factor) were transplanted into the cord injury site. We checked the BBB scores to evaluate the functional recovery in each group at 8 weeks after transplantation. We then, finally checked the neural cell differentiation with double immunofluorescence staining, and we also analyzed the axonal regeneration with retrograde labelling of brain stem neurons by using fluorogold. The HUCBs transplanted group improved, more than the control group at every week after transplantation, and also, the BDNF enabled an improvement of the BBB locomotion scores since the 1 week after its application (P<0.05). 8 weeks after transplantation, the HUCBs with BDNF transplanted group had more greatly improved BBB scores, than the other groups (P<0.001). The transplanted HUCBs were differentiated into various neural cells, which were confirmed by double immunoflorescence staining of BrdU and GFAP & MAP-2 staining. The HUCBs and BDNF each have individual positive effects on axonal regeneration. The HUCBs can differentiate into neural cells and induce motor function improvement in the cord injured rat models. Especially, the BDNF has effectiveness for neurological function improvement due to axonal regeneration in the early cord injury stage. Thus the HUCBs and BDNF have recovery effects of a moderate degree for cord injured rats.

Low-cost label-free electrical detection of artificial DNA nanostructures using solution-processed oxide thin-film transistors.

A high-sensitivity, label-free method for detecting deoxyribonucleic acid (DNA) using solution-processed oxide thin-film transistors (TFTs) was developed. Double-crossover (DX) DNA nanostructures with different concentrations of divalent Cu ion (Cu(2+)) were immobilized on an In-Ga-Zn-O (IGZO) back-channel surface, which changed the electrical performance of the IGZO TFTs. The detection mechanism of the IGZO TFT-based DNA biosensor is attributed to electron trapping and electrostatic interactions caused by negatively charged phosphate groups on the DNA backbone. Furthermore, Cu(2+) in DX DNA nanostructures generates a current path when a gate bias is applied. The direct effect on the electrical response implies that solution-processed IGZO TFTs could be used to realize low-cost and high-sensitivity DNA biosensors.

Approaches to label-free flexible DNA biosensors using low-temperature solution-processed InZnO thin-film transistors.

Low-temperature solution-processed In-Zn-O (IZO) thin-film transistors (TFTs) exhibiting a favorable microenvironment for electron transfer by adsorbed artificial deoxyribonucleic acid (DNA) have extraordinary potential for emerging flexible biosensor applications. Superb sensing ability to differentiate even 0.5 μL of 50 nM DNA target solution was achieved through using IZO TFTs fabricated at 280 °C. Our IZO TFT had a turn-on voltage (V(on)) of -0.8 V, on/off ratio of 6.94 × 10(5), and on-current (I(on)) value of 2.32 × 10(-6)A in pristine condition. A dry-wet method was applied to immobilize two dimensional double crossover tile based DNA nanostructures on the IZO surface, after which we observed a negative shift of the transfer curve accompanied by a significant increase in the Ion and degradation of the Von and on/off ratio. As the concentration of DNA target solution increased, variances in these parameters became increasingly apparent. The sensing mechanism based on the current evolution was attributed to the oxidation of DNA, in which the guanine nucleobase plays a key role. The sensing behavior obtained from flexible biosensors on a polymeric substrate fabricated under the identical conditions was exactly analogous. These results compare favorably with the conventional field-effect transistor based DNA sensors by demonstrating remarkable sensitivity and feasibility of flexible devices that arose from a different sensing mechanism and a low-temperature process, respectively.

Effect of human mesenchymal stem cell transplantation combined with growth factor infusion in the repair of injured spinal cord

Recently, bone marrow stromal cells have been shown to have the capacity to differentiate into neural cell under experimental cell culture conditions. Some investigators suppose that these cells, when placed into an environment of injury, express factors that promote repair or active compensatory mechanisms and endogeneous stem cells within the injured tissue. Rats were subjected to a weight driven implant spinal cord injury. After one week, the rats were treated with cultured human mesenchymal stem cells (MSCs) transplantation and basic fibroblast growth factor (bFGF) infusion into the CSF space. Functional outcome and histologic evaluation were performed. The data showed improved functional outcome in the group treated with MSCs transplantation and bFGF administration compared with the group of MSCs transplantation and control, which means bFGF might take an additional role to improve functional outcome. Glial differentiation of MSCs was noted but neuronal differentiation was doubtful. In this study, we did not demonstrate the mechanism of the neurotrophic factor affecting neural repair. However, this study is consistent with growing literature that MSCs and neurotrophic factor promote tissue repair and functional recovery after spinal cord injury and suggests that MSCs transplantation and bFGF warrants investigation as a therapeutic intervention after spinal cord injury.

Enhanced Electrical Characteristics and Stability via Simultaneous Ultraviolet and Thermal Treatment of Passivated Amorphous In–Ga–Zn–O Thin-Film Transistors

We developed a method to improve the electrical performance and stability of passivated amorphous In-Ga-Zn-O thin-film transistors by simultaneous ultraviolet and thermal (SUT) treatment. SUT treatment was carried out on fully fabricated thin-film transistors, including deposited source/drain and passivation layers. Ultraviolet (UV) irradiation disassociated weak and diatomic chemical bonds and generated defects, and simultaneous thermal annealing rearranged the defects. The SUT treatment promoted densification and condensation of the channel layer by decreasing the concentration of oxygen-vacancy-related defects and increasing the concentration of metal-oxide bonds. The SUT-treated devices exhibited improved electrical properties compared to nontreated devices: field-effect mobility increased from 5.46 to 13.36 V·s, sub-threshold swing decreased from 0.49 to 0.32 V/decade, and threshold voltage shift (for positive bias temperature stress) was reduced from 5.1 to 1.9 V.

Recent advances in low-temperature solution-processed oxide backplanes

Applicable flexible electronics, particularly flexible displays, have been developed for next-generation devices in recent years. Sol–gel processing, for example, which uses low-temperature annealing, is a promising technique. This review article focuses on recent advances in achieving low-temperature, solution-processed oxide thin-film transistors (TFTs) through chemical and physical approaches. First, chemical approaches were overviewed in terms of solute and solvent engineering. Second, physical approaches were summarized that some researchers added energy resources except heat on the conventional sol–gel process. The additional energy sources involve microwave annealing, high-pressure annealing, and ultraviolet irradiation. This review article offers an overview of these techniques introduced in details. From these efforts, metal-oxide TFTs can be fabricated at 150°C maintaining their device performance.

Artificial DNA nanostructure detection using solution-processed In-Ga-Zn-O thin-film transistors

A method for detecting artificial DNA using solution-processed In-Ga-Zn-O (IGZO) thin-film transistors (TFTs) was developed. The IGZO TFT had a field-effect mobility (μFET) of 0.07 cm2/Vs and an on-current (Ion) value of about 2.68 μA. A dry-wet method was employed to immobilize double-crossover (DX) DNA onto the IGZO surface. After DX DNA immobilization, significant decreases in μFET (0.02 cm2/Vs) and Ion (0.247 μA) and a positive shift of threshold voltage were observed. These results were attributed to the negatively charged phosphate groups on the DNA backbone, which generated electrostatic interactions in the TFT device.A method for detecting artificial DNA using solution-processed In-Ga-Zn-O (IGZO) thin-film transistors (TFTs) was developed. The IGZO TFT had a field-effect mobility (μFET) of 0.07 cm2/Vs and an on-current (Ion) value of about 2.68 μA. A dry-wet method was employed to immobilize double-crossover (DX) DNA onto the IGZO surface. After DX DNA immobilization, significant decreases in μFET (0.02 cm2/Vs) and Ion (0.247 μA) and a positive shift of threshold voltage were observed. These results were attributed to the negatively charged phosphate groups on the DNA backbone, which generated electrostatic interactions in the TFT device.

Study of nitrogen high-pressure annealing on InGaZnO thin-film transistors.

We studied the effects of high-pressure annealing (HPA) on InGaZnO (IGZO) thin-film transistors (TFTs). HPA was proceeded after TFT fabrication as a post process to improve electrical performance and stability. We used N2 as the pressurized gas. The applied pressures were 1 and 3 MPa at 200 °C. For N2 HPA under 3 MPa at 200 °C, field-effect mobility and the threshold voltage shift under a positive bias temperature stress were improved by 3.31 to 8.82 cm(2)/(V s) and 8.90 to 4.50 V, respectively. The improved electrical performance and stability were due to structural relaxation by HPA, which leads to increased carrier concentration and decreased oxygen vacancy.

Electrical responses of artificial DNA nanostructures on solution-processed In-Ga-Zn-O thin-film transistors with multistacked active layers.

We propose solution-processed In-Ga-Zn-O (IGZO) thin-film transistors (TFTs) with multistacked active layers for detecting artificial deoxyribonucleic acid (DNA). Enhanced sensing ability and stable electrical performance of TFTs were achieved through use of multistacked active layers. Our IGZO TFT had a turn-on voltage (V(on)) of -0.8 V and a subthreshold swing (SS) value of 0.48 V/decade. A dry-wet method was adopted to immobilize double-crossover DNA on the IGZO surface, after which an anomalous hump effect accompanying a significant decrease in V(on) (-13.6 V) and degradation of SS (1.29 V/decade) was observed. This sensing behavior was attributed to the middle interfaces of the multistacked active layers and the negatively charged phosphate groups on the DNA backbone, which generated a parasitic path in the TFT device. These results compared favorably with those reported for conventional field-effect transistor-based DNA sensors with remarkable sensitivity and stability.

Low-voltage driving solution-processed nickel oxide based unipolar resistive switching memory with Ni nanoparticles

Resistive random access memory (RRAM) combines the advantages of nonvolatile flash memory and volatile dynamic random access memory, avoiding their drawbacks. For the practical use of RRAM, achieving low-voltage driving is strongly desired. Here we report the effect of Ni nanoparticles on solution-processed NiO based RRAM which can realize a one diode one resistor operation by unipolar resistive switching mode and low-voltage driving for future demands. The Ni nanoparticles not only contributed to high oxygen mobility, but also affected effective insulator thickness reduction, and stoichiometric variation in NiO thin films. Furthermore, the Ni nanoparticle embedded device demonstrated good reliability. These findings can enhance the applicability of RRAM as a next generation memory device.