J.H. Jung

Physical characterization of emulsion intercalated polyaniline-clay nanocomposite

Using emulsion polymerization method, polyaniline (PAN)‐Na a ‐montmorillonite (MMT) clay nanocomposites were synthesized. Dodecylbenzenesulfonic acid (DBSA) was used as an emulsifier and dopant during emulsion polymerization. The X-ray diAraction patterns showed that PAN‐DBSA was intercalated between clay layers in the order of nanoscale. The room temperature (RT) dc conductivities of nanocomposites were 1‐10 ˇ3 S=cm depending on the molar ratio of dopants used. Temperature dependence of dc conductivity for the nanocomposites followed a quasi-one-dimensional (1D) variable range hopping (VRH) model. From temperature dependence of electron paramagnetic resonance experiments, magnetic properties and the density of states of the systems were obtained. The doping level of the nanocomposites was deduced from the results of X-ray photoelectron spectroscopy experiments. From the comparison of physical properties between PAN with clay and PAN without clay, the eAects of dopant and the layer of clay on charge transport and structure are discussed. ” 2001 Elsevier Science B.V. All rights reserved.

Effect of dopant and clay on nanocomposites of polyaniline (PAN) intercalated into Na+-montmorillonite (Na+-MMT)

The nanocomposites of polyaniline (PAN) and Na + -montmorillonite (Na + - MMT) were synthesized by emulsion polymerization using dodecylbenzenesulfonic acid (DBSA) or camphorsulfonic acid (CSA) as dopant and emulsifier. In the X-ray diffraction patterns of the systems, we observed that the layer of conducting PAN-DBSA or PAN-CSA between the clay layers was in nanoscale layers (< 10 A). The temperature dependence of dc conductivity [σ dc (T)] for the nanocomposites followed a quasi-one dimensional (ID) variable range hopping (VRH) model. The σ dc (T) varied with the dopant used and the molar ratio. From temperature dependent EPR experiments, we obtained the magnetic susceptibility and the line width of the system. The Na + -MMT clay layer plays important role for interchain interaction of the system. The effects of dopant and the layer of Na + -MMT on charge transport and structure are discussed.

Electrical, magnetic, and structural properties of lithium salt doped polyaniline

Abstract We report the results of temperature dependence of dc conductivity σ dc ( T ), electron paramagnetic resonance (EPR), and X-ray photoelectron spectroscopy (XPS) experiments for the polyaniline (PAN) doped with various lithium (Li) salts such as LiPF 6 , LiBF 4 , LiClO 4 , LiAsF 6 , and LiCF 3 SO 3 . A quasi one-dimensional (1D) variable range hopping (VRH) model provide the best fitting for σ dc ( T ) the Li salt doped PAN samples, which is similar to that of protonic acid (HCl) doped polyaniline samples. The σ dc and its temperature dependence vary with the kind of Li salts used. Temperature dependence of thermoelectric power of PAN doped with LiPF 6 shows the metallic behavior. From EPR experiments, we obtain that χ P depends on the kind of Li salts. The results of XPS experiments are discussed to account for the doping procedure with Li salts. Temperature dependence of EPR linewidths and X-ray diffraction patterns are compared for the various Li salt doped PAN samples. The insulator–metal transition of PAN-LiPF 6 samples is also discussed.

Extremely low-frequency electromagnetic fields induce neural differentiation in bone marrow derived mesenchymal stem cells.

Extremely low-frequency electromagnetic fields (ELF-EMF) affect numerous biological functions such as gene expression, cell fate determination and even cell differentiation. To investigate the correlation between ELF-EMF exposure and differentiation, bone marrow derived mesenchymal stem cells (BM-MSCs) were subjected to a 50-Hz electromagnetic field during in vitro expansion. The influence of ELF-EMF on BM-MSCs was analysed by a range of different analytical methods to understand its role in the enhancement of neural differentiation. ELF-EMF exposure significantly decreased the rate of proliferation, which in turn caused an increase in neuronal differentiation. The ELF-EMF-treated cells showed increased levels of neuronal differentiation marker (MAP2), while early neuronal marker (Nestin) was down-regulated. In addition, eight differentially expressed proteins were detected in two-dimensional electrophoresis maps, and were identified using ESI-Q-TOF LC/MS/MS. Among them, ferritin light chain, thioredoxin-dependent peroxide reductase, and tubulin β-6 chain were up-regulated in the ELF-EMF-stimulated group. Ferritin and thioredoxin-dependent peroxide reductase are involved in a wide variety of functions, including Ca2+ regulation, which is a critical component of neurodegeneration. We also observed that the intracellular Ca2+ content was significantly elevated after ELF-EMF exposure, which strengthens the modulatory role of ferritin and thioredoxin-dependent peroxide reductase, during differentiation. Notably, western blot analysis indicated significantly increased expression of the ferritin light chain in the ELF-EMF-stimulated group (0.60 vs. 1.08; P < 0.01). These proteins may help understand the effect of ELF-EMF stimulation on BM-MSCs during neural differentiation and its potential use as a clinically therapeutic option for treating neurodegenerative diseases.

Modulation of biomechanical properties of hyaluronic acid hydrogels by crosslinking agents

Modulation of both mechanical properties and biocompatibilities of hyaluronic acid (HA) hydrogels is very importance for their applications in biomaterials. Pure HA solution was converted into a hydrogel by using butanediol diglycidyl ether (BDDE) as a crosslinking agent. Mechanical properties of the HA hydrogels have been evaluated by adding up different amount of BDDEs. While the mechanical properties of the obtained HA hydrogels were evaluated by measuring their crosslinking degrees, elastic modulus and viscosity, their in vitro biocompatibilities were done by measuring the degrees of anti-inflammatory reactions, cell viabilities and cytotoxicity. The degrees of anti-inflammatory reactions were determined by measuring the amount of nitric oxides (NOs) released from lipopolysaccharide(LPS)(+)-induced macrophages; cell viability was evaluated by observing differences in the behaviors of fibroblasts covered with the HA hydrogels, compared with those covered with the films of Teflon and Latex. Cytotoxicity of the HA hydrogels was also evaluated by measuring the degrees of viability of the cells exposed on the extracts of the HA hydrogels over those of Teflon, Latex and pure HA solutions by the assays of thiazoly blue tetrazolium bromide (MTT), neutral reds, and bromodeoxyuridine (BrdU). The results showed that employment of BDDEs beyond critical amounts showed lower biocompatibility of the crosslinked HA hydrogels but higher crosslinking degrees and mechanical properties, indicating the importance of controlling the HA concentrations, BDDE amounts and their reaction times for the synthesis of the crosslinked HA hydrogels for their clinical applications as biomaterials.

Insulator-metal transition of Li salts doped polyaniline

The results of dc conductivity (σ dc ), X-ray photoelectron spectroscopy (XPS), and electron paramagnetic resonance (EPR) for Li salts (LiPF 6 , LiBF 4 ) doped polyaniline (PAN) are reported. Temperature (T) dependence of σ dc of LiPF 6 or LiBF 4 doped PAN samples shows lnσ dc T -1/2 arising from a quasi-one-dimensional (ID) variable range hopping (VRH) model. As molar concentration increases, the insulator-metal transition is observed in the results of σ dc and the density of states obtained from EPR experiments. The doping levels of the systems are obtained from XPS nitrogen (N) Is peak analysis. The doping process and the insulator-metal transition of Li salts doped PAN samples are compared with those of HCl doped PAN samples.

Inhibition of c-Yes induces differentiation of HT-29 human colon cancer stem cells through midbody elongation

Recent research suggests that a small group of cells, named cancer stem cells (CSCs), is responsible for initiating tumor formation, recurrence, and metastasis. c-Yes, a proto-oncogene that is a subfamily of Src family kinase, is often activated in human colon cancer; this implicates c-Yes in the onset and progression of the disease. The objective of this study was to investigate the correlation between c-Yes and CSCs. We performed a sphere formation assay and reverse transcription-polymerase chain reaction for studying the differentiation of HT-29 human colon CSCs. To demonstrate the specific role of c-Yes in CSCs, we performed live cell microscopy and a cell cycle assay. These study shows, for the first time, that c-Yes is enriched in CD133+ CSCs, compared to their CD133− counterparts, and that c-Yes depletion in CD133+ cells induces cell differentiation. Moreover, c-Yes depletion was found to elongate the midbody and increase the proliferation doubling time. This also suggested that the misregulation of microtubules during chromosomal separation causes aneuploidy. Our results suggest that c-Yes may play a crucial role in initiating, maintaining, and driving the tumorigenic property of colon cancer.