53 research outputs found

    Understanding poly(2-hydroxyethyl methacrylate) (PHEMA) hydrogel as a multifunctional membrane in microfluidic cell culture platform

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    Cell culture technology developed at the turn of 20th century using Petri dish, which is not able to consider the microenvironment that the cells experience in vessels, has remained virtually unchanged for almost a century. However, such microenvironment associated with cell culture which usually consists of soluble factors, extracellular matrix cues, and cellular networks is difficult to reproduce experimentally with the traditional approach. In order to further elaborate complex mechanisms of cell biology through mimicking such microenvironment in vivo, the technical approaches together with developed microdevices are highly demanded within such a context. Microfluidic devices have been extensively developed and used for cell culture in the last two decades, which offer numerous advantages and a great potential for accurate and efficient control of the complex culturing microenvironment at cellular length scale. However, these devices are relatively complex in their fabrication and integration to fulfil multifunctional tasks for cell culture and drug testing simultaneously, which for example requires a membrane between the culture chamber and drug delivery reservoir to control microenvironment at cellular scale. This thesis is to primarily focus on the feasibility and reliability in the attempt of using poly(2-hydroxyethyl methacrylate) (PHEMA) hydrogel as an inserted membrane, based on its permeable and flexible tissue-like properties. PHEMA membrane is able to serve dual purposes in the microfluidic systems in cell culture: i) exchanging nutrients between culture chamber and drug delivery reservoir; and ii) sealing the microchannel circuits.</div

    Microstructural and mechanical characteristics of PHEMA-based nanofibre-reinforced hydrogel under compression

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    Natural network-structured hydrogels (e.g. bacterial cellulose (BC)) can be synthesised with specific artificial hydrogels (e.g. poly(2-hydroxyethyl methacrylate)(PHEMA)) to form a tougher and stronger nanofibre-reinforced composite hydrogel, which possesses micro- and nano-porous structure. These synthetic hydrogels exhibit a number of advantages for biomedical applications, such as good biocompatibility and better permeability for molecules to pass through. In this paper, the mechanical properties of this nanofibre-reinforced hydrogel containing BC and PHEMA have been characterised in terms of their tangent modulus and fracture stress/strain by uniaxial compressive testing. Numerical simulations based on Mooney-Rivlin hyperelastic theory are also conducted to understand the internal stress distribution and possible failure of the nanofibre-reinforced hydrogel under compression. By comparing the mechanical characteristics of BC, PHEMA, and PHEMA-based nanofibre reinforced hydrogel (BC-PHEMA) under the compression, it is possible to develop a suitable scaffold for tissue engineering on the basis of fundamental understanding of mechanical and fracture behaviours of nanofibre-reinforced hydrogels

    Quantum Phase Slips in 6 mm Long Niobium Nanowire

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    Transport measurements were made to study the superconducting transition of four 6 mm long niobium nanowires with different cross-sectional dimensions. A low-temperature residual resistance tail measured with an excitation current of 5 nA is found in the thinnest wire down to 50 mK or 7.7% of <i>T</i><sub>c</sub> of Nb. The functional form of the residual resistance is consistent with quantum phase slip (QPS) processes. Resistance measured at high bias excitation current switches among many discrete values that are well below the normal state resistance. These discrete resistance values as a function of temperature fall into several parallel curves all showing QPS-like decay in the low temperature limit similar to that found at low current. The coexistence of QPS-like resistance tails and resistance jumps found in the same wire unifies results from previous experiments where these two distinct sets of evidence for QPS are exclusive of each other

    Graphical demonstration of attenuation rates corresponding to different wavelengths when light propagates in water.

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    Blue travels the longest because it has the shortest wavelength. This is one of the main reasons why underwater images often appear blue [1].</p

    The overall structure of our model.

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    The first step is to input the underwater image of the degradation domain, reconstruct the features through the generator G(Ix), and extract the features from the two images by the encoder Genc. Then the Que-Attn module selects the important features to establish the contrastive loss. The generated image is input to the discriminator for identification, and then the parameters of the whole network are updated.</p

    Coacervate of Polyacrylamide and Cationic Gemini Surfactant for the Extraction of Methyl Orange from Aqueous Solution

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    Coacervation in aqueous solution of the mixture of cationic ammonium surfactant hexamethylene-1,6-bis­(dodecyl­dimethyl­ammonium bromide) (12-6-12) and 10% hydrolyzed polyacrylamide (PAM) has been investigated. It was found that the 12-6-12/PAM mixture forms coacervate with a large network structure over a wide concentration range of surfactant and polyelectrolyte and shows great efficiency in the extraction of Methyl Orange (MO) from water owing to the cooperation of hydrophobic, electrostatic, and π-cation interactions. Meanwhile, the dye joins the coacervate and strengthens the network structure of the coacervate. In particular, benefiting from partial excess of 12-6-12 molecules, the coacervate phase presents selective adsorption behavior toward anionic dye MO in the presence of cationic dye methylene blue (MB). Furthermore, the coacervate phase is utilized to modify quartz sand and melamine foam, and the coacervate-treated adsorbents can adsorb MO efficiently. Moreover, the MO-loaded adsorbents are easily regenerated with hydrochloric acid, making this an inexpensive and environmentally benign process. These findings offer a simple and effective alternative for the treatment of dye contaminated water and the recovery of dyes

    Nanoporous Hollow Transition Metal Chalcogenide Nanosheets Synthesized <i>via</i> the Anion-Exchange Reaction of Metal Hydroxides with Chalcogenide Ions

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    Nanoporous hollow transition metal chalcogenides are of special interest for a variety of promising applications. Although some advanced synthetic methods have been reported, the development of a facile and general strategy to fabricate porous hollow nanostructures of transition metal chalcogenides, especially with enhanced electrocatalytic performance, still remains highly challenged. Herein, we report a facile chemical transformation strategy to prepare nanoporous hollow Co<sub>3</sub>S<sub>4</sub> nanosheets <i>via</i> the anion exchange reaction of Co(OH)<sub>2</sub> with sulfide ions. The chemical transformation mechanism involves the as-formed layer of nanoporous cobalt sulfide on Co(OH)<sub>2</sub> driven by the anion-exchange-reaction and lattice mismatch induced quick strain release, a following diffusion-effect-dominated core–shell hollow intermediate with hollow interiors, and subsequent Ostwald ripening growth of hollow nanosheets at elevated temperatures. This anion-exchange strategy of transition metal hydroxides with chalcogenide ions is also suitable for fabricating nanoporous hollow nanosheets of other metal chalcogenides (<i>e.g.</i>, CoSe<sub>2</sub>, CoTe<sub>2</sub>, CdS, and NiS). The as-prepared nanoporous hollow Co<sub>3</sub>S<sub>4</sub> nanosheets are found to be highly active and stable for electrocatalytic oxygen evolution reaction

    Effective Modulation of Interlayer Excitons in WSe<sub>2</sub>/WS<sub>2</sub> Heterostructures by Plasmon–Exciton Interaction

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    Effective charge transfer and carrier separation at the interface are paramount for optimizing the performance of devices based on van der Waals heterostructures. In this investigation, surface plasmons generated by gold nanoparticles are employed to modulate the photocarrier dynamics in WSe2/WS2 heterostructures. The results of pump–probe measurements reveal that the efficiency of carrier transfer across the WSe2/WS2 heterostructure interface can be significantly enhanced via energy transfer mechanisms mediated by gold plasmons. Moreover, the electric field engendered by the plasmonic oscillations can modulate the dipole moment of the interlayer exciton. These well-aligned excitons avoid annihilation, and the extension of the lifetime of the excitons with increased pump power is realized by a screening effect. The findings presented herein offer valuable insights into the active manipulation of charge transfer and extend our understanding of the integral role played by plasmon–exciton coupling in mediating charge separation in van der Waals heterostructures

    Two-Step Freezing in Alkane Monolayers on Colloidal Silica Nanoparticles: From a Stretched-Liquid to an Interface-Frozen State

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    The crystallization behavior of an archetypical soft/hard hybrid nanocomposite, that is, an <i>n-</i>octadecane C<sub>18</sub>/SiO<sub>2</sub>-nanoparticle composite, was investigated by a combination of differential scanning calorimetry (DSC) and variable-temperature solid-state <sup>13</sup>C nuclear magnetic resonance (VT solid-state <sup>13</sup>C NMR) as a function of silica nanoparticles loading. Two latent heat peaks prior to bulk freezing, observed for composites with high silica loading, indicate that a sizable fraction of C<sub>18</sub> molecules involve two phase transitions unknown from the bulk C<sub>18</sub>. Combined with the NMR measurements as well as experiments on alkanes and alkanols at planar amorphous silica surfaces reported in the literature, this phase behavior can be attributed to a transition toward a 2D liquid-like monolayer and subsequently a disorder-to-order transition upon cooling. The second transition results in the formation of a interface-frozen monolayer of alkane molecules with their molecular long axis parallel to the nanoparticles’ surface normal. Upon heating, the inverse phase sequence was observed, however, with a sizable thermal hysteresis in accord with the characteristics of the first-order phase transition. A thermodynamic model considering a balance of interfacial bonding, chain stretching elasticity, and entropic effects quantitatively accounts for the observed behavior. Complementary synchrotron-based wide-angle X-ray diffraction (WAXD) experiments allow us to document the strong influence of this peculiar interfacial freezing behavior on the surrounding alkane melts and in particular the nucleation of a rotator phase absent in the bulk C<sub>18</sub>

    Table_1_The influential factors and non-pharmacological interventions of cognitive impairment in children with ischemic stroke.XLSX

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    BackgroundThe prevalence of pediatric ischemic stroke rose by 35% between 1990 and 2013. Affected patients can experience the gradual onset of cognitive impairment in the form of impaired language, memory, intelligence, attention, and processing speed, which affect 20–50% of these patients. Only few evidence-based treatments are available due to significant heterogeneity in age, pathological characteristics, and the combined epilepsy status of the affected children.MethodsWe searched the literature published by Web of Science, Scopus, and PubMed, which researched non-pharmacological rehabilitation interventions for cognitive impairment following pediatric ischemic stroke. The search period is from the establishment of the database to January 2022.ResultsThe incidence of such impairment is influenced by patient age, pathological characteristics, combined epilepsy status, and environmental factors. Non-pharmacological treatments for cognitive impairment that have been explored to date mainly include exercise training, psychological intervention, neuromodulation strategies, computer-assisted cognitive training, brain-computer interfaces (BCI), virtual reality, music therapy, and acupuncture. In childhood stroke, the only interventions that can be retrieved are psychological intervention and neuromodulation strategies.ConclusionHowever, evidence regarding the efficacy of these interventions is relatively weak. In future studies, the active application of a variety of interventions to improve pediatric cognitive function will be necessary, and neuroimaging and electrophysiological measurement techniques will be of great value in this context. Larger multi-center prospective longitudinal studies are also required to offer more accurate evidence-based guidance for the treatment of patients with pediatric stroke.</p
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