Self-assembly mechanism of PEG-b-PCL and PEG-b-PBO-b-PCL amphiphilic copolymer micelles in aqueous solution from coarse grain modeling

We followed the self-assembly of high-molecular weight MePEG- b -PCL (poly(methyl ethylene glycol)-block-poly(ε-caprolactone)) diblock and MePEG- b -PBO- b -PCL (poly(methyl ethylene glycol)-block-poly(1,2-butylene oxide)-block-poly(ε-caprolactone)) into micelles using molecular dynamics simulation with a coarse grain (CG) force field based on quantum mechanics (CGq FF). The triblock polymer included a short poly(1,2-butylene oxide) (PBO) at the hydrophilic-hydrophobic interface of these systems. Keeping the hydrophilic length fixed (MePEG₄₅), we considered 250 chains in which the hydrophobic length changed from PCL₄₄ or PBO₆- b -PCL₄₃ to PCL₆₂ or PBO₉- b -PCL₆₁. The polymers were solvated in explicit water for 2 μs of simulations at 310.15 K. We found that the longer diblock system undergoes a morphological transition from an intermediate rod-like micelle to a prolate-sphere, while the micelle formed from the longer triblock system is a stable rod-like micelle. The two shorter diblock and triblock systems show similar self-assembly processes, both resulting in slightly prolate-spheres. The dynamics of the self-assembly is quantified in terms of chain radius of gyration, shape anisotropy, and hydration of the micelle cores. The final micelle structures are analyzed in terms of the local density components. We conclude that the CG model accurately describes the molecular mechanisms of self-assembly and the equilibrium micellar structures of hydrophilic and hydrophobic chains, including the quantity of solvent trapped inside the micellar core.     

Effects of Structural Variations on the Cellular Response and Mechanical Properties of Biocompatible,Biodegradable, and Porous Smectic Liquid Crystal Elastomers

The authors report on series of side‐chain smectic liquid crystal elastomer (LCE) cell scaffolds based on star block‐copolymers featuring 3‐arm, 4‐arm, and 6‐arm central nodes. A particular focus of these studies is placed on the mechanical properties of these LCEs and their impact on cell response. The introduction of diverse central nodes allows to alter and custom‐modify the mechanical properties of LCE scaffolds to values on the same order of magnitude of various tissues of interest. In addition, it is continued to vary the position of the LC pendant group. The central node and the position of cholesterol pendants in the backbone of ε‐CL blocks (alpha and gamma series) affect the mechanical properties as well as cell proliferation and particularly cell alignment. Cell directionality tests are presented demonstrating that several LCE scaffolds show cell attachment, proliferation, narrow orientational dispersion of cells, and highly anisotropic cell growth on the as‐synthesized LCE materials.

     

A Robust Method to Generate Mechanically Anisotropic Vascular Smooth Muscle Cell Sheets for Vascular Tissue Engineering

In arterial tissue engineering, mimicking native structure and mechanical properties is essential because compliance mismatch can lead to graft failure and further disease. With bottom‐up tissue engineering approaches, designing tissue components with proper microscale mechanical properties is crucial to achieve the necessary macroscale properties in the final implant. This study develops a thermoresponsive cell culture platform for growing aligned vascular smooth muscle cell (VSMC) sheets by photografting N‐isopropylacrylamide (NIPAAm) onto micropatterned poly(dimethysiloxane) (PDMS). The grafting process is experimentally and computationally optimized to produce PNIPAAm–PDMS substrates optimal for VSMC attachment. To allow long‐term VSMC sheet culture and increase the rate of VSMC sheet formation, PNIPAAm–PDMS surfaces were further modified with 3‐aminopropyltriethoxysilane yielding a robust, thermoresponsive cell culture platform for culturing VSMC sheets. VSMC cell sheets cultured on patterned thermoresponsive substrates exhibit cellular and collagen alignment in the direction of the micropattern. Mechanical characterization of patterned, single‐layer VSMC sheets reveals increased stiffness in the aligned direction compared to the perpendicular direction whereas nonpatterned cell sheets exhibit no directional dependence. Structural and mechanical anisotropy of aligned, single‐layer VSMC sheets makes this platform an attractive microstructural building block for engineering a vascular graft to match the in vivo mechanical properties of native arterial tissue.

     

Error and stability analysis of numerical solution for the time fractional nonlinear Schrödinger equation on scattered data of general‐shaped domains

In present work, a kind of spectral meshless radial point interpolation (SMRPI) technique is applied to the time fractional nonlinear Schrödinger equation in regular and irregular domains. The applied approach is based on erudite combination of meshless methods and spectral collocation techniques. The point interpolation method with the help of radial basis functions is used to construct shape functions which play as basis functions in the frame of SMRPI. It is proved the scheme is unconditionally stable with respect to the time variable in and also convergent by the order of convergence , . In the current work, the thin plate spline are used as the basis functions and to eliminate the nonlinearity, a simple predictor‐corrector (P‐C) scheme is performed. It is shown that the SMRPI solution, as a complex function, is suitable one for the time fractional nonlinear Schrödinger equation. The results of numerical experiments are compared to analytical solutions to confirm the reliable treatment of these stable solutions. © 2016 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 33: 1043–1069, 2017     

考虑底部隆起的浅埋隧道围岩压力计算分析

针对浅埋隧道开挖后底部隆起变形现象,应用极限分析上限法构造了考虑底部隆起变形的围岩压力计算模型,结合线性Mohr-Coulomb准则等推导出极限围岩压力的理论表达式。通过约束条件将围岩压力的计算转化为数学中的最优化问题,编制程序进行了优化计算。将计算结果与工程实测数据及文献计算结果进行了对比,验证了当前方法的可靠性。同时,指出在运用极限分析法处理浅埋隧道围岩压力问题过程中应将隧道底部一同考虑,对隧道底部支护会对整个围岩压力产生影响,有助于隧道结构的整体稳定。研究可以为浅埋隧道的开挖、支护提供一定的理论指导.     

Evolutionary Boussinesq model with nonmonotone friction and heat flux boundary conditions

In this paper we prove the existence and regularity of a solution to a two-dimensional system of evolutionary hemivariational inequalities which describes the Boussinesq model with nonmonotone friction and heat flux. We use the time retardation and regularization technique, combined with a regularized Galerkin method, and recent results from the theory of hemivariational inequalities.     

Photophysics of Fluorescent Contact Sensors Based on the Dicyanodihydrofuran Motif

Fluorescent molecular rotors have been used for measurements of local mobility on molecular length scales, for example to determine viscosity, and for the visualization of contact between two surfaces. In the present work, we deepen our insight into the excited-state deactivation kinetics and mechanics of dicyanodihydrofuran-based molecular rotors. We extend the scope of the use of this class of rotors for contact sensing with a red-shifted member of the family. This allows for contact detection with a range of excitation wavelengths up to ∼600 nm. Steady-state fluorescence shows that the fluorescence quantum yield of these rotors depends not only on the rigidity of their environment, but – under certain conditions – also on its polarity. While excited state decay via rotation about the exocyclic double bond is rapid in nonpolar solvents and twisting of a single bond allows for fast decay in polar solvents, the barriers for both processes are significant in solvents of intermediate polarity. This effect may also occur in other molecular rotors, and it should be considered when applying such molecules as local mobility probes.     

磷矿及磷肥中氧化钙测定方法改进

为了解决磷矿及磷肥中氧化钙酸溶不完全和消除测定过程中磷酸根、镁、铁等的干扰,对磷矿和磷肥中氧化钙的测定方法进行改进。对不同酸溶解体系选择、酸用量、加热时间、干扰掩蔽实验、pH值等条件进行实验,确定采用10 mL王水、3 mL氢氟酸分解试样,加入2 mL盐酸溶解盐类,加入10 mL糊精和5 mL三乙醇胺溶液掩蔽Mg^2+、Fe^3+、PO4^3-、Al^3+的干扰,无需过滤,在pH≈7时预加EDTA至溶液清亮,再加入KOH调节溶液pH>13,加入适量的钙黄绿素指示剂,用EDTA溶液滴定至绿色荧光消失,测定磷矿和磷肥中氧化钙。实验结果表明,三个磷矿石标准样品和磷肥监控样氧化钙测定的相对标准偏差(RSD,n=11)为0.21%~1.1%。实际磷矿和磷肥样品中氧化钙测定值与国家标准方法测定结果一致。