Robust and Adhesive Hydrogels from Cross‐Linked Poly(ethylene glycol) and Silicate for Biomedical Use

A systematic approach to develop robust and adhesive hydrogels by photopolymerizing poly(ethylene glycol) (PEG)‐diacrylate and methoxy‐PEG‐acrylate in the presence of charged silicate nanoparticles (Laponite) is presented. PEG‐diacrylate and silicate are used for covalent and physical cross‐linking, thus providing the hydrogel with mechanical and adhesive strengths. Methoxy‐PEG‐acrylate is used as a softening agent. The resulting hydrogels can be extensively elongated and the hydrogels readily adhere to tissue even in the elongated state. These hydrogels may aid the development of adhesive tissue engineering matrixes, wound dressings, sealants, and the adhesive components of biomedical devices.

     

Carbon fiber-reinforced rectangular isolators with compressible elastomer: Analytical solution for compression and bending

The behavior of multilayer elastomeric isolators employing carbon fibers as reinforcement material rather than steel has been considered. This kind of reinforcement is used to make the isolators lighter and cheaper, since carbon fibers (or Kevlar) are much more resistant per unit weight than steel. From the mechanical point of view, the main difference is that the fiber reinforcement cannot be considered rigid in extension as it is usually done for steel plates. In this paper an analytical model to analyze the compression and bending behavior of fiber-reinforced rectangular isolators is presented. The model takes into account, for the first time, both the reinforcement extensibility and the compressibility of the elastomer. An analytical solution to predict deformations, stresses and stiffness is here determined in terms of Fourier series, both for compression and bending.     

受压橡胶海绵圆筒的轴对称平面应变问题研究

针对橡胶海绵材料圆筒受压问题,根据欧拉-拉格朗日变分原理,建立了基于Blatz-Ko材料模型的轴对称平面应变问题的非线性微分方程. 采用参数变换的方法,获得了该问题的参数形式解析解. 并通过相应数值算例,得到了径向应力和切向应力沿圆筒径向的变化规律,以及过盈量对径向应力和切向应力影响规律.      

Metallocene catalysts for olefin polymerizations. XXIV. Stereoblock propylene polymerization catalyzed by rac-[anti-ethylidene(1-η5-tetramethylcyclopentadienyl)(1-η5-indenyl)dimethyltitanium: A two-state propagation

Racemic-anti-[ethylidene(1-η⁵-tetramethylcyclopentadienyl) (1-η⁵-indenyl)dimethyltitanium ( 6 ) has been synthesized and its molecular structure determined by x-ray diffraction methods. The two Ti?Me(1) and Ti?Me(2) units have bond distances differing by 0.08 Å and their proton NMR resonances are separated by over 1 ppm. Using this compound and methylaluminoxane (MAO) as the activator, at 25°C the 6 /MAO catalyst produced polypropylene having crystalline domain with physical crosslinks. The polymers obtained at lower polymerization temperatures are rheologically liquids. The behaviors of this catalyst system resembles closely the previously reported rac-[anti-ethylidene(1-η⁵-tetramethylcyclopentadienyl) (1-η⁵-indenyl)dichlorotitanium ( 4 )/MAO system. The structure of 6 determined here furnishes tangible support for the proposed two-state (isomeric)-switching propagation mechanism. Addition of MAO to 6 causes broadening of the Me(1) resonance in the ¹H-NMR spectra, and 6 is decomposed by Ph₃C⁺B(C₆F₅)^-₄. © 1992 John Wiley & Sons, Inc.     

Second-Order Estimates for the Macroscopic Response and Loss of Ellipticity in Porous Rubbers at Large Deformations

This work presents the application of a recently proposed second-order homogenization method (Ponte Castañeda, 2002) to generate estimates for effective behavior and loss of ellipticity in hyperelastic porous materials with random microstructures that are subjected to finite deformations. The main concept behind the method is the introduction of an optimally selected linear thermoelastic comparison composite, which can then be used to convert available linear homogenization estimates into new estimates for the nonlinear hyperelastic composite. In this paper, explicit results are provided for the case where the matrix is taken to be isotropic and strongly elliptic. In spite of the strong ellipticity of the matrix phase, the homogenized second-order estimates for the overall behavior are found to lose ellipticity at sufficiently large compressive deformations corresponding to the possible development of shear band-type instabilities (Abeyaratne and Triantafyllidis, 1984). The reasons for this result have been linked to the evolution of the microstructure, which, under appropriate loading conditions, can induce geometric softening leading to overall loss of ellipticity. Furthermore, the second-order homogenization method has the merit that it recovers the exact evolution of the porosity under a finite-deformation history in the limit of incompressible behavior for the matrix. Mathematics Subject Classifications (2000) 49S05, 74B20, 74Q15, 74Q05.     

Stress-strain relations for elastomeric foams in uni-, bi- and tri-axial compression modes

Summary Based on suggestions given in [1], the uni-axial compressive stress-strain relations for elastomeric foams, which were developed in [2], have been extended to cover the bi- and tri-axial stress modes of compression for both open- and closed-cell elastomeric foams.The stress-strain relations for uni- and tri-axial stress compression modes were validated by comparing numerical predictions, which were based on them, to experimental results.     

Effect of Elastomeric Nanoparticles on Toughness and Heat Resistance of Epoxy Resins

A new composite consisting of epoxy resin and elastomeric nanoparticles with high toughness and high heat‐distortion temperature is prepared. The size of the nanoparticles used was less than 90 nm. The excellent properties of the composite seem to be due to stronger interactions between the carboxyl groups of the nanoparticles and the epoxy groups of the resin, and to enhanced hydrogen bonding between the nitrile groups of the rubber and the hydroxyl groups of the resin.     

Water as a Link between Membrane and Colloidal Theories for Cells

This review is an attempt to incorporate water as a structural and thermodynamic component of biomembranes. With this purpose, the consideration of the membrane interphase as a bidimensional hydrated polar head group solution, coupled to the hydrocarbon region allows for the reconciliation of two theories on cells in dispute today: one considering the membrane as an essential part in terms of compartmentalization, and another in which lipid membranes are not necessary and cells can be treated as a colloidal system. The criterium followed is to describe the membrane state as an open, non-autonomous and responsive system using the approach of Thermodynamic of Irreversible Processes. The concept of an open/non-autonomous membrane system allows for the visualization of the interrelationship between metabolic events and membrane polymorphic changes. Therefore, the Association Induction Hypothesis (AIH) and lipid properties interplay should consider hydration in terms of free energy modulated by water activity and surface (lateral) pressure. Water in restricted regions at the lipid interphase has thermodynamic properties that explain the role of H-bonding networks in the propagation of events between membrane and cytoplasm that appears to be relevant in the context of crowded systems.     

Silicon micropillar electrodes of lithiumion batteries used for characterizing electrolyte additives

The <100> crystal-oriented silicon micropillar array platforms were prepared by microfabrication processes for the purpose of electrolyte additive identification. The silicon micropillar array platform was used for the study of fluorinated vinyl carbonate (FEC), vinyl ethylene carbonate (VEC), ethylene sulfite (ES), and vinyl carbonate (VC) electrolyte additives in the LiPF₆ dissolved in a mixture of ethylene carbonate and diethyl carbonate electrolyte system using charge/discharge cycles, electrochemical impedance spectroscopy, cyclic voltammetry, scanning electron microscopy, and x-ray photoelectron spectroscopy. The results show that the silicon pillar morphology displays cross-shaped expansion after lithiation/delithiation, the inorganic lithium salt keeps the silicon pillar morphology intact, and the organic lithium salt content promotes a rougher silicon pillar surface. The presence of poly-(VC) components on the surface of FEC and VC electrodes allows the silicon pillar to accommodate greater volume expansion while remaining intact. This work provides a standard, fast, and effective test method for the performance analysis of electrolyte additives and provides guidance for the development of new electrolyte additives.