43 research outputs found

    Learning in Hybrid-Project Systems: The Effects of Project Performance on Repeated Collaboration

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    This study advances contingency theories of performance-outcome learning in hybrid-project systems, in which both project participants and superordinate organizations influence the formation of project ventures. We propose that performance-outcome learning depends on the perceived relevance of prior performance and on organizational control over project participants. We examine this framework using data on 239 U.S. movie projects from the years 1931-40. In keeping with our theory, higher project performance led to future collaborations with the same partners, contingent on prior collaborations, project similarity, and organizational control. Our findings imply distinct patterns of network evolution and unfolding adaptation of hybrid-project systems through slow-moving, local adjustments

    Electrically Conductive PEDOT Coating with Self-Healing Superhydrophobicity

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    A self-healing electrically conductive superhydrophobic poly­(3,4-ethylenedioxythiophene) (PEDOT) coating has been prepared by chemical vapor deposition of a fluoroalkylsilane (POTS) onto a PEDOT film, which was obtained by electrochemical deposition. The coating not only maintained high conductivity with a low resistivity of 3.2 × 10<sup>–4</sup> Ω·m, but also displayed a water contact angle larger than 156° and a sliding angle smaller than 10°. After being etched with O<sub>2</sub> plasma, the coating showed an excellent self-healing ability, spontaneously regaining its superhydrophobicity when left under ambient conditions for 20 h. This superhydrophobicity recovery process was found to be humidity-dependent, and could be accelerated and completed within 2 h under a high humidity of 84%. The coating also exhibited good superhydrophobicity recovering ability after being corroded by strong acid solution at pH 1 or strong base solution at pH 14 for 3 h

    “Fastening” Porphyrin in Highly Cross-Linked Polyphosphazene Hybrid Nanoparticles: Powerful Red Fluorescent Probe for Detecting Mercury Ion

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    It is a significant issue to overcome the concentration-quenching effect of the small fluorescent probes and maintain the high fluorescent efficiency at high concentration for sensitive and selective fluorescent mark or detection. We developed a new strategy to “isolate” and “fasten” porphyrin moieties in a highly cross-linked poly­(tetraphenylporphyrin-<i>co</i>-cyclotriphosphazene) (TPP–PZS) by the polycondensation of hexachlorocyclotriphosphazene (HCCP) and 5,10,15,20-tetrakis­(4-hydroxyphenyl)­porphyrin (TPP-(OH)<sub>4</sub>) in a suitable solvent. The resulting TPP–PZS particles were characterized with transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier transform infrared (FTIR), <sup>31</sup>P nuclear magnetic resonance (NMR), and ultraviolet and visible (UV–vis) absorption spectra. Remarkably, TPP–PZS particles obtained in acetone emitted a bright red fluorescence both in powder state and in solution because the aggregation of porphyrin moieties in “H-type” (face-to-face) and “J-type” (edge-to-edge) was effectively blocked. The fluorescent TPP–PZS particles also showed superior resistance to photobleaching, and had a high sensitivity and selectivity for the detection of Hg<sup>2+</sup> ions. The TPP–PZS particles were therefore used as an ideal material for preparing test strips to quickly detect/monitor the Hg<sup>2+</sup> ions in a facile way

    Electro-Responsively Reversible Transition of Polythiophene Films from Superhydrophobicity to Superhydrophilicity

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    An electro-responsively reversible switching of wettability between superhydrophobicity and superhydrophilicity has been obtained from a highly porous structured polythiophene film. The polythiophene film was prepared by two-step electrochemical deposition on an indium tin oxide (ITO) substrate. The underlying poly­(3,4-ethylenedioxythiophene) (PEDOT) provides a highly porous structured conductive support, and poly­(3-methylthiophene) (P­(3-MTH)) deposited thereon plays the role of a low-surface-energy conductive coating. The wettability switching of this double-layer film between superhydrophobicity and superhydrophilicity has been investigated by doping and dedoping in an electrolyte solution containing ClO<sub>4</sub><sup>–</sup>. Electrochromism of the film was also seen to accompany the electrochemical process of conversion between the two superwetting states. On the basis of this porous electro-active film, an in situ electro-wetting device was also demonstrated

    Facile Synthesis of Superparamagnetic Fe<sub>3</sub>O<sub>4</sub>@polyphosphazene@Au Shells for Magnetic Resonance Imaging and Photothermal Therapy

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    Multifunctional nanoparticles were prepared by directly welding superparamagnetic Fe<sub>3</sub>O<sub>4</sub> nanoparticles and Au shells together with highly cross-linked polyphosphazene as “glue” in a facile but effective way. The as-prepared particles can simultaneously take advantages of both magnetization of Fe<sub>3</sub>O<sub>4</sub> core for magnetic resonance imaging diagnosis and strong near-infrared absorption of Au nanoshell for photothermal therapy

    Anisotropic Fluorescence Emission of Ionic Complex Induced by the Orientation of Azobenzene Unit

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    A series of azobenzene-containing fluorescent complexes with stilbene fluorescent unit were prepared based on the ionic self-assembly approach. The incorporation of the stilbene unit did not change the lamellar structure of the azobenzene-containing complex. Under pulsed laser irradiation, the azobenzene group oriented in the direction perpendicular to the laser polarization, and as a result, the fluorescent stilbene unit was cooperatively oriented following the direction of azobenzene group orientation. This oriented complex films presented anisotropic emission of fluorescence, and the anisotropic ratio of fluorescence increases with the increase of the content of azobenzene unit in the complex

    Precise Preparation of a Multilayer Tubular Cell Sheet with Well-Aligned Cells in Different Layers to Simulate Native Arteries

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    Compared with artificial vascular grafts, bottom-up tubular cell sheets (TCSs) without scaffolds have shown promise for patients with cardiovascular disease. However, TCS therapy also faces the challenges of lengthy maturation time, elaborate operation, and weak mechanical strength. In this work, a structured small-diameter vascular graft (SDVG), consisting of three layers of TCSs, with different cell types and arrangements, was fabricated using layer-by-layer assembly of naturally formed TCSs and further cell culture. To this end, a surface-patterned collagen-coated cylindrical substrate was designed for the efficient harvesting of naturally formed and well-aligned TCSs. The patterned collagen (type I) layer facilitated the adhesion and orientation of cells, and a continuous tubular cell monolayer was naturally formed after approximately 4 days in cell culture. Biocompatible near-infrared (NIR) light was used to trigger the photothermal phase transition of the collagen coated on the cylindrical substrate to dissociate the collagen layer. As a result, an intact TCS could be harvested within a few minutes. These naturally formed and well-aligned TCSs exhibited outstanding free-standing performance without rugosity, facilitating their operability and practical application. A ring tensile test showed that orientation was critical for improving the mechanical properties of TCSs. The layer-by-layer assembly of SDVGs not only is easy to manipulate and has a short preparation time but also overcomes the bottleneck of forming a hierarchically structured vascular graft. This approach shows promise for repairing damaged blood vessels

    Highly Cross-Linked and Biocompatible Polyphosphazene-Coated Superparamagnetic Fe<sub>3</sub>O<sub>4</sub> Nanoparticles for Magnetic Resonance Imaging

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    Highly cross-linked and biocompatible poly­(cyclotriphosphazene-<i>co</i>-4,4′-sulfonyldiphenol) (PZS) were used to directly coat hydrophilic superparamagnetic Fe<sub>3</sub>O<sub>4</sub> nanoparticles by a facile but effective one-pot polycondensation. The obtained core–shell Fe<sub>3</sub>O<sub>4</sub>@PZS nanohybrids were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) and X-ray diffraction spectra. Interesting, the size and T<sub>2</sub> relaxivity of Fe<sub>3</sub>O<sub>4</sub>@PZS increased with increasing the mass ratio of Fe<sub>3</sub>O<sub>4</sub> to PZS. All these nanohybrids could be internalized by HeLa cells but show negligible cytotoxicity. The PZS layer slowly degraded into less dangerous forms such as 4,4′-sulfonyldiphenol, phosphate and ammonia at neutral or acid atmosphere. Considering their excellent water dispersibility, colloidal and chemical stability, magnetic manipulation, and magnetic resonance imaging (MRI) properties, Fe<sub>3</sub>O<sub>4</sub>@PZS nanohybrids have great potential in MRI diagnosis of cancer

    Dual-Responsive Ionically Assembled Fluorescent Nanoparticles from Copoly(Ionic Liquid) for Temperature Sensor

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    A simple copolymer, copoly­(ionic liquid), consisting of <i>N</i>-isopropylacrylamide (NIPAM) and 1-benzyl-4-vinylpyridine bromide (4-VPBn<sup>+</sup>Br<sup>–</sup>) units as thermo-responsive and ionic liquid parts, respectively, has been synthesized. Fluorescent nanoparticles (FNPs) were then formed under the driving forces of electrostatic interaction between 2-(4-amino-2-hydroxyphenyl) benzothiazole derivative (AHBTA) and copoly­(ionic liquid) due to hydrophilic/hydrophobic balance. The fluorescent intensity of the FNPs enhanced by a factor of about 50 times when the pH was increased from 7 to 10, and was effectively doubled within 1 °C around LCST in pH 9 buffer solution, thus showing a dramatic pH and thermal dual-dependent property. The FNPs exhibited reversible fluorescence enhancement/quenching over more than five cycles, regardless of the heating/cooling process. Furthermore, the FNPS proved to be much more stable to UV light irradiation than pure fluorescence molecule AHBTA

    Precise Preparation of a Multilayer Tubular Cell Sheet with Well-Aligned Cells in Different Layers to Simulate Native Arteries

    No full text
    Compared with artificial vascular grafts, bottom-up tubular cell sheets (TCSs) without scaffolds have shown promise for patients with cardiovascular disease. However, TCS therapy also faces the challenges of lengthy maturation time, elaborate operation, and weak mechanical strength. In this work, a structured small-diameter vascular graft (SDVG), consisting of three layers of TCSs, with different cell types and arrangements, was fabricated using layer-by-layer assembly of naturally formed TCSs and further cell culture. To this end, a surface-patterned collagen-coated cylindrical substrate was designed for the efficient harvesting of naturally formed and well-aligned TCSs. The patterned collagen (type I) layer facilitated the adhesion and orientation of cells, and a continuous tubular cell monolayer was naturally formed after approximately 4 days in cell culture. Biocompatible near-infrared (NIR) light was used to trigger the photothermal phase transition of the collagen coated on the cylindrical substrate to dissociate the collagen layer. As a result, an intact TCS could be harvested within a few minutes. These naturally formed and well-aligned TCSs exhibited outstanding free-standing performance without rugosity, facilitating their operability and practical application. A ring tensile test showed that orientation was critical for improving the mechanical properties of TCSs. The layer-by-layer assembly of SDVGs not only is easy to manipulate and has a short preparation time but also overcomes the bottleneck of forming a hierarchically structured vascular graft. This approach shows promise for repairing damaged blood vessels
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