Early vasopressin initiation for pediatric patients with vasodilatory shock after cardiac surgery

Objective Vasopressin has showed a beneficial use in pediatric patients with vasodilatory shock after cardiac surgery. However, the optimal timing of vasopressin initiation has not been investigated.Our aim was to evaluate the effect of early vasopressin initiation for these patients.

Dual Nanofillers-Reinforced Noncovalently Cross-Linked Polymeric Composites with Unprecedented Mechanical Strength

Noncovalentlycross-linkedpolymermaterials through healing,recycling,and reprocessing can reduce materials consumption and alleviate environmental pollution.However,it remains a huge challenge to fabricate super-strong noncovalently cross-linked polymer materials with mechanical strength comparable to high-performance engineering polymers.Herein,healable and reprocessable noncovalently cross-linked polymer compositeswith an unprecedented mechanical strength are fabricated by complexation of polyacrylic acid(PAA),polyvinylpyrrolidone(PVPON),and carbonized polymer dots(CPDs)(denoted as PAA-PVPON-CPDs).The incorporation of 15 wt%CPDs generates PAA-PVPON-CPDs compositeswith a tensile strength of∼158 MPa and Young’s modulus of∼8.2GPa.Servingas nanofillers,theCPDs can establish strong interactions with polymers in PAA-PVPON composites.The CPDs and the in situ-formed PAAPVPON nanoparticles work in concert to significantly strengthen the PAA-PVPON-CPDs composites to an unprecedented strength.The PAA-PVPON-CPDs composites exhibit excellent impact resistance and damage tolerance because of the high mechanical strength of the composites and the energy dissipation mechanism of the CPDs and PAA-PVPON nanoparticles.Moreover,the fractured PAA-PVPON-CPDs composites can be healed to restore their original mechanical strength.

Visualization of Macrophase Separation and Transformation in Immiscible Polymer Blends

Identification and visualization of phase structures inside polymer blends are of critical importance in the understanding of their intrinsic structure and dynamics.However,the direct optical observation of the individual component phase in a dense bulk material poses a significant challenge.Herein,three-dimensional fluorescence imaging of phase separation and realtime visualization of phase transformation in immiscible polymer blends of polypropylene and polystyrene is realized through multiphoton laser scanning microscopy.Owing to the specific fluorescence behavior of the cyanostyrene derivative 2-(4-bromophenyl)-3-(4-(4-(diphenylamino)styryl)phenyl)fumaronitrile,the high-contrast imaging of the macrophase of the component polymer in two and three dimensions with a maximum depth of 140μm and a high signal-to-noise ratio of 300 can be achieved.Detailed spectroscopic and structural studies reveal that the distinctive fluorescence features of each phase domain should originate from the formation of a completely different aggregate between probes and component polymer.Furthermore,visualizations of the internal morphology deformation and macrophase transformation were realized by employing a stretched dumbbell sample under constant tension.

Coil to globule transition of homo- and block-copolymer with different topological constraint and chain stiffness

In this paper, we present the coil-to-globule(CG) transitions of homopolymers and multiblock copolymers with different topology and stiffness by using molecular dynamics with integrated tempering sampling method. The sampling method was a novel enhanced method that efficiently sampled the energy space with low computational costs. The method proved to be efficient and precise to study the structural transitions of polymer chains with complex topological constraint, which may not be easily done by using conventional Monte Carlo method. The topological constraint affects the globule shape of the polymer chain, thus further influencing the CG transition. We found that increasing the topological constraint generally decreased CG transition temperature for homopolymers. For semiflexible chains, an additional first-order like symmetry-broken transition emerged. For block copolymers, the topological constraint did not obviously change the transition temperature, but greatly reduced the energy signal of the CG transition.

Intramolecular hydrogen bonds in a single macromolecule:Strength in high vacuum versus liquid environments

As a weak non-covalent interaction,hydrogen bond(H-bond)is highly susceptible to the environmental interference.However,the direct quantification of a single H-bond under an interference-free condition is still a challenge.Herein,the intramolecular H-bond in a model system,poly(N-isopropylacrylamide),is studied in high vacuum by single-molecule atomic force microscopy and steered molecular dynamics simulations,which allows the precise quantification of H-bond strength in an interference-free state.Control experiments show that the H-bond is significantly weakened in nonpolar solvent,even if the dielectric constant is very close to vacuum.If a polar solvent is used as the environment,the H-bond will be further weaker or even broken.These results imply that for experiments in any liquid environment,the H-bond strength(△G)will be only -50% or even less of that measured in vacuum.Further analysis shows that in liquid environments,AG decays in a quasi-linear way with the increase of the dielectric constant(ε).For H-bond studies in future,the result measured in vacuum can be set as the standard value,namely,the inherent strength.This approach will provide fundamental insights into the H-bond participated nano-structures and materials in different environments.

A study of chemical reactions in coarse-grained simulations

We introduce a reaction model for use in coarse-grained simulations to study the chemical reactions in polymer systems at mesoscopic level.In this model,we employ an idea of reaction probability in control of the whole process of chemical reactions.This model has been successfully applied to the studies of surface initiated polymerization process and the network structure formation of typical epoxy resin systems.It can be further modified to study different kinds of chemical reactions at mesoscopic scale.