Polymeric ultrafine fibrous membranes (UFMs) with high thermal stability and high whiteness are highly desired in modern optoelectronic applications. A series of fluoro-containing polyimide (FPI) ...UFMs with high whiteness, good thermal stability, and good hydrophobicity were prepared via a one-step electrospinning procedure from the organo-soluble FPI resins derived from a fluoro-containing dianhydride, 4,4′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA), and various diamines containing either pendant trifluoromethyl (–CF3) groups or alicyclic units in the side chains. The obtained FPI UFMs, including FPI-1 from 6FDA and 3,5-diaminobenzotrifluoride (TFMDA), FPI-2 from 6FDA and 2′-trifluoromethyl-3,4′-oxydianiline (3FODA), FPI-3 from 6FDA and 1,4-bis(4-amino-2-trifluoromethyl)phenoxybenzene (6FAPB), FPI-4 from 4,4′-bis(4-amino-2-trifluoromethyl)phenoxybiphenyl (6FBAB), and FPI-5 from 6FDA and 4′-tert-butyl-cyclohexyl-3,5-diaminobenzoate (DABC) showed whiteness indices (WI) higher than 87.00 and optical reflectance values higher than 80% at the wavelength of 457 nm (R457), respectively. The FPI-5 UFM, especially, showed the highest WI of 92.88. Meanwhile, the prepared PI UFMs exhibited good hydrophobic features with water contact angles (WCA) higher than 105°. At last, the PI UFMs exhibited good thermal stability with glass transition temperatures (Tg) higher than 255 °C, and the 5% weight-loss temperatures (T5%) higher than 510 °C in nitrogen.
The formation of polymeric micro-patterns on various substrates via a photolithography procedure has been widely used in semiconductor fabrication. Standard polymer patterns are usually fabricated ...via photosensitive polymer varnishes, in which large amounts of potentially harmful solvents with weight ratios over 50 wt% have to be removed. In the current work, a novel pattern-formation methodology via solvent-free electrospun photosensitive polymeric fibrous membranes (NFMs) instead of the conventional photosensitive solutions as the starting photoresists was proposed and practiced. For this purpose, a series of preimidized negative auto-photosensitive polyimide (PSPI) resins were first prepared via the two-step chemical imidization procedure from the copolymerization reactions of 3,3′,4,4′-benzophenonetetracarboxylic- dianhydride (BTDA) and two ortho-methyl-substituted aromatic diamines, including 3,3′,5,5′-tetramethyl-4,4′-diaminodiphenylmethane (TMMDA) and 3,7-diamino-2,8-dimethyl- dibenzothiophene sulfone (TSN). The derived homopolymer PI-1 (BTDA-TMMDA) and the copolymers, including SPI-2~SPI-6, with the molar ratio of 5~25% for TSN in the diamine units, showed good solubility in polar solvents. Then, a series of PSPI NFMs were fabricated via standard electrospinning procedure with the developed PSPI solutions in N,N-dimethylacetamide (DMAc) with a solid content of 25 wt% as the starting materials. The derived PSPI NFMs showed good thermal stability with 5% weight loss temperatures higher than 500 °C in nitrogen. Meanwhile, the derived PSPIs showed good photosensitivity to the ultraviolet (UV) emitting wavelengths of i-line (365 nm), g-line (405 nm) and h-line (436 nm) of the high-pressure mercury lamps in both forms of transparent films and opaque NFMs. Fine micro-patterns with a line width of around 100 μm were directly obtained from the representative SPI-4 NFM via standard photolithography procedure.
Polyimide (PI) has been widely used as the alignment layers for twisted-nematic (TN) thin film transistor driven liquid crystal display devices (TFT-LCDs). However, the currently PI alignment layers ...based on 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA) and common aromatic diamines usually showed low alignment abilities to rigid-rod liquid crystal (LC) molecule with low pretilt angles. Thus, in the current work, a series of novel PI precursors, poly(amic acid)s (PAAs) alignment agents were developed. For this purpose, four PAAs have been prepared from a newly developed ester-linked aromatic diamine containing
tert
-butyl-substituted cyclohexyl in the side chain, 4'-
tert
-butyl-cyclohexyl-3,5-diaminobenzoate (DABC) and various dianhydrides. The PAAs included three ones derived from aliphatic or alicyclic dianhydrides, including PAA-1 (BDA-DABC) from 1,2,3,4-butanetetracarboxylic dianhydride (BDA), PAA-2 (CBDA-DABC) from CBDA, and PAA-3 (DMCBDA-DABC) from 1,3-dimethyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride (DMCBDA), and one from aromatic dianhydride, 2,2′-bis(3,4-dicarboxylphenyl)hexafluoropropane dianhydride (6FDA) (PAA-4, 6FDA-DABC). The derived PAAs were used as the alignment agents to fabricate the minicells of twisted-nematic (TN) modes of thin-film transistor driven liquid crystal display (TFT-LCDs). The PI alignment layers obtained by the thermal imidization of the corresponding PAAs, followed by rubbing treatments showed good alignment ability to the liquid crystal (LC) molecules with the pretilt angles (
θ
p
) in the range of 1.46 ~ 7.02°. PI-3 (DMCBDA-DABC) showed the highest
θ
p
of 7.02°, while PI-4 (6FDA-DABC) exhibited the lowest one of 1.46°. The semi-aromatic PI-1 ~ PI-3 layers showed higher optical transmittance than that of the wholly aromatic PI-4 counterpart. PI-4 layer exhibited the lowest voltage holding ratio (VHR) of 91.32% at 60 °C, which was apparently lower than those of the semi-aromatic PI-1 ~ PI-3 counterparts (> 96.00%). In addition, the semi-alicyclic PI alignment layers (PI-2 and PI-3) showed lower residual direct circuit voltages (RDC) than that of the wholly aromatic PI-4. At last, the photoalignment behaviors of the PI alignment layers were preliminarily investigated. Only PI-2 and PI-3 exhibited the alignment ability to the LC molecules after being treated with the linear polarized ultraviolet (LPUV) with the wavelength of 254 nm.
Intercellular adhesions between renal glomerular epithelial cells (also called podocytes) are necessary for the proper function of the glomerular filtration barrier. Although our knowledge of the ...molecular composition of podocyte cell-cell contact sites has greatly progressed, the underlying molecular mechanism regulating the formation of these cell-cell contacts remains largely unknown. We have used forskolin, an activator of adenylyl cyclase that elevates the level of intracellular cAMP, to investigate the effect of cAMP and three Rho-family small GTPases (RhoA, Cdc42, and Rac1) on the regulation of cell-cell contact formation in a murine podocyte cell line. Transmission electron microscopy and the immunostaining of cell adhesion molecules and actin-associated proteins have revealed a structural change at the site of cell-cell contact following forskolin treatment. The activity of the Rho-family small GTPases before and after forskolin treatment has been evaluated with a glutathione-S-transferase pull-down assay. Forskolin reinforces the integrity of cell-cell contacts, resulting in the closure of an intercellular adhesion zipper, accompanied by a redistribution of cell adhesion molecules and actin-associated proteins in a continuous linear pattern at cell-cell contacts. The Rho-family small GTPases Rac1 and Cdc42 are activated during closure of the adhesion zipper, whereas RhoA is suppressed. Thus, cAMP promotes the assembly of cell-cell contacts between podocytes via a mechanism that probably involves Rho-family small GTPases.
The renal glomerular podocyte exhibits a highly arborized morphology. In comparison with the neuron, which is the best studied process‐bearing cell, the podocyte major processes share many cell ...biological characteristics with neuronal dendrites. Both podocytes and neurons develop microtubule‐based thick processes with branching morphology and both have thin actin‐based projections (i.e. podocyte foot processes and dendritic spines). Formation of podocyte processes and neuronal dendrites depends on the assembly of microtubules. Because the assembly of microtubules is regulated by phosphorylation of microtubule‐associated proteins, inhibition of protein phosphatases abolishes and inhibition of protein kinases promotes process formation. Podocytes and dendrites also share the machinery of intracellular traffic of membranous vesicles, as well as cytoskeletal elements, which is indispensable for the elongation of these processes. Furthermore, these two cell types share expression of various molecules working for signal transduction, transmembranous transport and intercellular contacts. Such common gene expression implies a similar transcriptional regulation in these cells. Concerning the formation of podocyte foot processes and dendritic branches, actin filaments are thought to play a central role in orchestrating the function of various molecules and the regulation of actin assembly is necessary to establish and maintain such sophisticated cellular architecture. The molecular mechanism of foot process formation seems to include Rho family small GTP‐binding proteins, which are known to be responsible for the establishment of dendritic branching morphology.
The first event occurring at the boundary between a metal implant and living tissue is the attachment of cells onto the metal surface of the implant. The attachment characteristics of the metal in ...this situation are critical in determining its biocompatibility and usefulness as artificial bone and tooth implants. Using the human osteosarcoma cell line Saos-2, we attempted to establish simple and reliable methods for evaluating the attachment of cultured osteoblastic cells onto titanium samples that had been subjected to various surface treatments. Fluorescence actin imaging showed that cells cultured on titanium with hydrofluoric acid etching (HF-Ti) exhibited delayed spreading of their cytoplasm, as compared to cells cultured for the same length of time on nitrided titanium or physically polished titanium. The HF-Ti-cultured cells also exhibited poor assembly of focal contacts, as visualized by vinculin immunofluorescence. Furthermore, in motility assays based on an in vitro wound model, cells cultured on HF-Ti migrated more slowly than cells cultured on other titanium surfaces. These data suggest that Saos-2 cells attach less effectively to the HF-Ti surface. The methods described in this study should be useful for assessing the initial interactions of cultured cells with various materials, including metals.
Podocytes, renal glomerular visceral epithelial cells, have two kinds of processes, namely major processes containing microtubules (MTs) and foot processes with actin filaments (AFs). The present ...study investigated how MTs are organized by the Rho-ROCK signal transduction pathway during process formation of podocytes.
After induction of differentiation, podocytes of the conditionally immortalized mouse cell line were treated with Y-27632, a specific inhibitor of ROCK, and exoenzyme C3, an inhibitor of RhoA, as well as with forskolin whose effects include inhibition of RhoA, in order to inhibit the Rho-ROCK pathway.
Inhibition of ROCK significantly enhanced the formation of thick processes containing MT bundles. Y-27632 promoted process formation even in the presence of latrunculin A which disrupts AFs, strongly suggesting that ROCK directly regulates MT assembly. Treatment with Y-27632 increased MT stability, and stabilized MTs preferentially localized in podocyte processes. Moreover, when treated with a combination of Y-27632 and forskolin, and with Y-27632 and C3 as well, podocytes developed not only MT-based thick processes but also AF-based thin projections.
These data indicate a contribution of ROCK in MT organization to promote podocyte process formation, although it was originally thought to regulate AF assembly. AF-based thin projections seem to be induced mainly by inhibition of RhoA and ROCK. The present study reveals a significant role of the Rho-ROCK signal pathway in the reorganization of both MTs and AFs during process formation of podocytes.
In the developing central nervous system, apoptosis plays an important role in the normal organization of the neuronal circuit. The timing of neurogenesis, proliferation, and migration of the neurons ...in the developing olfactory bulb (OB) is well studied; however, the involvement of apoptosis in this process is not fully understood. In this study, we examined the changes in the distribution and the number of apoptotic cells in the rat OB during embryonic and postnatal periods, by using terminal deoxynucleotidyl transferase-mediated dUTP-digoxigenin nick end-labeling (TUNEL) staining. Although the number of TUNEL-positive cells was relatively small during the embryonic period, it gradually increased after birth, and peaked on postnatal day 20 with statistical significance, especially in the granule cell layer of the main OB. This transient increase of TUNEL-positive cells on postnatal day 20 may be involved in a critical event during maturation of the OB.
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