Chunyang Yu

A Supramolecular Janus Hyperbranched Polymer and Its Photoresponsive Self-Assembly of Vesicles with Narrow Size Distribution

Herein, we report a novel Janus particle and supramolecular block copolymer consisting of two chemically distinct hyperbranched polymers, which is coined as Janus hyperbranched polymer. It is constructed by the noncovalent coupling between a hydrophobic hyperbranched poly(3-ethyl-3-oxetanemethanol) with an apex of an azobenzene (AZO) group and a hydrophilic hyperbranched polyglycerol with an apex of a β-cyclodextrin (CD) group through the specific AZO/CD host-guest interactions. Such an amphiphilic supramolecular polymer resembles a tree together with its root very well in the architecture and can further self-assemble into unilamellar bilayer vesicles with narrow size distribution, which disassembles reversibly under the irradiation of UV light due to the trans-to-cis isomerization of the AZO groups. In addition, the obtained vesicles could further aggregate into colloidal crystal-like close-packed arrays under freeze-drying conditions. The dynamics and mechanism for the self-assembly of vesicles as well as the bilayer structure have been disclosed by a dissipative particle dynamics simulation.

An Injectable Enzymatically Crosslinked Carboxymethylated Pullulan/Chondroitin Sulfate Hydrogel for Cartilage Tissue Engineering

In this study, an enzymatically cross-linked injectable and biodegradable hydrogel system comprising carboxymethyl pullulan-tyramine (CMP-TA) and chondroitin sulfate-tyramine (CS-TA) conjugates was successfully developed under physiological conditions in the presence of both horseradish peroxidase (HRP) and hydrogen peroxide (H2O2) for cartilage tissue engineering (CTTE). The HRP crosslinking method makes this injectable system feasible, minimally invasive and easily translatable for regenerative medicine applications. The physicochemical properties of the mechanically stable hydrogel system can be modulated by varying the weight ratio and concentration of polymer as well as the concentrations of crosslinking reagents. Additionally, the cellular behaviour of porcine auricular chondrocytes encapsulated into CMP-TA/CS-TA hydrogels demonstrates that the hydrogel system has a good cyto-compatibility. Specifically, compared to the CMP-TA hydrogel, these CMP-TA/CS-TA composite hydrogels have enhanced cell proliferation and increased cartilaginous ECM deposition, which significantly facilitate chondrogenesis. Furthermore, histological analysis indicates that the hydrogel system exhibits acceptable tissue compatibility by using a mouse subcutaneous implantation model. Overall, the novel injectable pullulan/chondroitin sulfate composite hydrogels presented here are expected to be useful biomaterial scaffold for regenerating cartilage tissue.

Protein-Framed Multi-Porphyrin Micelles for a Hybrid Natural-Artificial Light-Harvesting Nanosystem.

A micelle-like hybrid natural-artificial light-harvesting nanosystem was prepared through protein-framed electrostatic self-assembly of phycocyanin and a four-armed porphyrin star polymer. The nanosystem has a special structure of pomegranate-like unimolecular micelle aggregate with one phycocyanin acceptor in the center and multiple porphyrin donors in the shell. It can inhibit donor self-quenching effectively and display efficient transfer of excitation energy (about 80.1 %) in water. Furthermore, the number of donors contributing to a single acceptor could reach as high as about 179 in this nanosystem.

Selective Degradation of Organic Pollutants Using an Efficient Metal-Free Catalyst Derived from Carbonized Polypyrrole via Peroxymonosulfate Activation

Metal-free carbonaceous materials, including nitrogen-doped graphene and carbon nanotubes, are emerging as alternative catalysts for peroxymonosulfate (PMS) activation to avoid drawbacks of conventional transition metal-containing catalysts, such as the leaching of toxic metal ions. However, these novel carbocatalysts face relatively high cost and complex syntheses, and their activation mechanisms have not been well-understood. Herein, we developed a novel nitrogen-doped carbonaceous nanosphere catalyst by carbonization of polypyrrole, which was prepared through a scalable chemical oxidative polymerization. The defective degree of carbon substrate and amount of nitrogen dopants (i.e., graphitic nitrogen) were modulated by the calcination temperature. The product carbonized at 800 °C (CPPy-F-8) exhibited the best catalytic performance for PMS activation, with 97% phenol degradation efficiency in 120 min. The catalytic system was efficient over a wide pH range (2-9), and the reaction of phenol degradation had a relatively low activation energy (18.4 ± 2.7 kJ mol-1). The nitrogen-doped carbocatalyst activated PMS through a nonradical pathway. A two-step catalytic mechanism was extrapolated: the catalyst transfers electrons to PMS through active nitrogen species and becomes a metastable state of the catalyst (State I); next, organic substrates are oxidized and degraded by serving as electron donors to reduce State I. The catalytic process was selective toward degradation of various aromatic compounds with different substituents, probably depending on the oxidation state of State I and the ionization potential (IP) of the organics; that is, only those organics with an IP value lower than ca. 9.0 eV can be oxidized in the CPPy-F-8/PMS system.

Ultrathin Alternating Copolymer Nanotubes with Readily Tunable Surface Functionalities

Well-defined ultrathin nanotubes (30 nm in diameter and of micrometer-scale length) were generated through the self-assembly of a novel alternative copolymer synthesized using an epoxy-thiol click-chemistry reaction. The self-assembly mechanism was investigated both by experiments and using dissipative particle dynamics (DPD) simulations. The obtained nanotubes can be readily functionalized with carboxy groups, amino groups, peptides, or other groups by simple modular click copolymerization.

Ductility dip cracking mechanism of Ni-Cr-Fe alloy based on grain boundary energy

Abstract Inconel 690 and the companion filler metal 52M (FM-52M) have susceptibility of ductility dip cracking (DDC) in welding procedure. According to test results, DDC was not only preferential to propagate on grain boundaries vertical to loading direction but also related to grain boundary structure. To reveal the relation of grain boundary angle and cracking, a three-dimensional polycrystalline model was constructed to simulate the formation of DDC. In this work, the initiation and propagation of DDC were studied based on extended Read–Shockley formula. The results indicate that grain boundaries with approximate 45° disorientation are most prone to cracking, and the simulated DDC morphology shows agreement with experimental results. The study provides an extra method to predict DDC propagation and helps to evaluate DDC susceptibility in grain level.

Computer Simulation Studies on the pH-Responsive Self-Assembly of Amphiphilic Carboxy-Terminated Polyester Dendrimers in Aqueous Solution

This paper investigates the pH-responsive self-assembly of an amphiphilic carboxyl-terminated polyester dendrimer, H20-COOH, in aqueous solution using the dissipative particle dynamics method. The electrostatic interactions were described by introducing the explicit interaction between the smeared charges on ionized polymer beads and the counterions. The results show that the self-assemblies could change from unimolecular micelles, microphase-separated small micelles, wormlike micelles, sheetlike micelles, and small vesicles to large vesicles with the decrease in the degree of ionization (α) of carboxylic acid groups. In addition, the detailed self-assembly mechanisms and the molecular packing models have also been disclosed for each self-assembly stages. Interestingly, the wormlike micelles are found to change from linear to branched when α decreases from 0.182 to 0.109. The current work might serve as a comprehensive understanding on the effect of carboxylic acid groups on the self-assembly behaviors of dendritic polymers.

Self-Restricted Green Fluorescent Protein Chromophore Analogues: Dramatic Emission Enhancement and Remarkable Solvatofluorochromism.

The confinement effect of the β-barrel defines the emission profiles of the chromophores of the green fluorescent protein (GFP) family. Here, we describe the design strategy and mimicking of confinement effects via the chromophore itself, termed the self-restricted effect. By systematically tailoring the GFP core, a family of 2,5-dialkoxy-substituted GFP chromophore analogues is found to be highly emissive and show remarkable solvatofluorochromism in fluid solvents. Fluorescence quantum yield (QY) and lifetime measurements, in combination with theoretical calculations, illustrate the mechanism relying on inhibition of torsional rotation around the exocyclic CC bond. Meanwhile, theoretical calculations further reveal that the electrostatic interaction between the solvent and the imidazolinone oxygen can contribute to suppress the radiationless decay channel around the exocyclic C═C double bond. Our findings put forward a universal approach toward unlocked highly emissive GFPc analogues, potentially promoting the understanding of the photophysics and biochemical application of GFP chromophore analogues.

Finite element simulation of butt welded 2·25Cr–1·6W steel pipe incorporating bainite phase transformation

Abstract This article presents a newly developed global optimisation method for the finite element simulation of welding process considering bainite transformation. In this method, the pattern search algorithm was applied to determine kinetic parameters in Johnson–Mehl–Avrami–Kolmogorov (JMAK) equation during a continuous cooling process. Meanwhile, the JMAK equation was modified into an explicit form as a function of welding temperature field to improve calculation efficiency in the optimisation process. This methodology improves the accuracy as calculating the temperature dependent volume fraction of bainite transformation in finite element simulation. The calculated welding residual stresses considering phase transformation effects exhibited better agreement with the measured results than those calculated without phase transformation. The influences of variable cooling rates on welding residual stresses were also investigated.

HBP Builder: A Tool to Generate Hyperbranched Polymers and Hyperbranched Multi-Arm Copolymers for Coarse-grained and Fully Atomistic Molecular Simulations.

Computer simulation has been becoming a versatile tool that can investigate detailed information from the microscopic scale to the mesoscopic scale. However, the crucial first step of molecular simulation is model building, particularly for hyperbranched polymers (HBPs) and hyperbranched multi-arm copolymers (HBMCs) with complex and various topological structures. Unlike well-defined polymers, not only the molar weight of HBPs/HBMCs with polydispersity, but the HBPs/HBMCs with the same degree of polymerization (DP) and degree of branching (DB) also have many possible topological structures, thus making difficulties for user to build model in molecular simulation. In order to build a bridge between model building and molecular simulation of HBPs and HBMCs, we developed HBP Builder, a C language open source HBPs/HBMCs building toolkit. HBP Builder implements an automated protocol to build various coarse-grained and fully atomistic structures of HBPs/HBMCs according to user’s specific requirements. Meanwhile, coarse-grained and fully atomistic output structures can be directly employed in popular simulation packages, including HOOMD, Tinker and Gromacs. Moreover, HBP Builder has an easy-to-use graphical user interface and the modular architecture, making it easy to extend and reuse it as a part of other program.