Design and validation of a vacuum assisted anchorage for the uniaxial tensile testing of soft materials

Current commercial tensile testing systems use spring-loaded or other compression-based grips to clamp materials in place posing a problem for very soft or delicate materials that cannot withstand this mechanical clamping force. In order to perform uniaxial tensile tests on soft tissues or materials, we have created a novel vacuum-assisted anchor (VAA). Fibrin gels were subjected to uniaxial extension, and the testing data was used to determine material mechanical properties. Utilizing the VAA, we achieved successful tensile breaks of soft fibrin gels while finding statistically significant differences between the mechanical properties of gels fabricated at two different fibrinogen concentrations.     

Optimization of clamping force for low-viscosity polymer injection molding

Due to its low cost and high efficiency, injection molding is used for the mass production of many plastic products nowadays. However, when processing low-viscosity plastic materials, i.e., materials with an excellent fluidity, an inappropriate setting of the clamping force often results in a poor appearance and dimensional accuracy of the final product. Thus, operators usually take the upper limit of the clamping force as a default in setting up the machine in an attempt to improve the quality of the molded parts. However, such an approach shortens the machine and mold life, increases the energy consumption, and leads to poor air venting. Consequently, more scientific methods for determining the clamping force setting are required. To meet this demand, the present study proposes a clamping force search methodology for determining the optimal clamping force setting of a hydraulic cylinder clamping injection molding machine in the processing of low-viscosity plastics such as thermoplastic polyurethane (TPU) and polypropylene (PP). Based on the characteristic extracted from the sensing tie-bar elongation profile under different clamping force settings, a regression analysis on these data points is implemented to seek for an optimal clamping force. The experimental results show that for an injection molding machine with a hydraulic cylinder clamping mechanism, the effect of the mold temperature on the clamping force is sufficiently small to be ignored, which has an impact on the toggle type clamping unit. Furthermore, compared to traditional methods, the optimal clamping force obtained using the method proposed in the present study results in a significant improvement in the yield rate. Overall, the results confirm that for low-viscosity polymer resins, the optimal clamping force determined using the proposed method results in a higher and more consistent quality of the molded parts than that achieved using the proper clamping force setting for ordinary-viscosity resins.     

The influence of deformation mode on the dynamic mechanical spectra of lightly plasticised PVC compositions

An assessment was made of the relative merits of various types of deformation mode to monitor variations in relaxation spectra of glassy polymers using dynamic mechanical tests.Rigid and lightly plasticised PVC compositions were used in view of the changes in the α and β relaxations that take place as a result of antiplasticisation and physical ageing phenomena.Large discrepancies were experienced in measurements of the modulus using cantilever deformation modes, while tan δ measurements and calculated values of the activation energies for the α and β processes were found to be less susceptible to variations in type of load imposed on the specimen.The axial pre-loading clamping arrangement was found to be the most accurate in characterising antiplasticisation phenomena, particularly when the static load was large in comparison with the dynamic excitation.     

Adhesive pi-clamping within synthetic multifunctional pores

We report the design, synthesis, and evaluation of synthetic multifunctional pores with adhesive, that is, electron-deficient naphthalenediimide (NDI) pi-clamps at their inner surface. We find that, in lipid bilayer membranes, comparable synthetic pores with and without pi-clamps have similar, nanomolar activity. Functional relevance of adhesive pi-clamping within synthetic pores is demonstrated by means of an innovative in situ blocker screening method. The obtained line of experimental evidence includes (a) different blockage efficiency with and without pi-clamps (quantified as clamping factors), (b) increasing clamping factors with increasing blocker charge (supportive ion pairing), and, most importantly, (c) increasing clamping factors with increasing aromatic electron donor-acceptor interactions. The availability of advanced synthetic multifunctional pores with refined active sites is important for practical applications in domains such as drug discovery (enzyme inhibitor screening) and diagnostics (multianalyte sensing).     

Ischemic change of organic acids in kidney

Organic acids in rabbit renal tissue biopsy were analyzed by capillary column gas chromatography--mas s spectrometry. The change of these organic acids under ischemic conditions was determined over 60 min after clamping the renal artery and vein. The results showed that lactic acid, glycolic acid, 2-hydroxybutyric acid, 3-hydroxypropionic acid, 2-methyl-glyceric acid, glyceric acid and malic acid increased at 4 and 6 min after clamping, but then decreased at 15 min. Glycerol increased 2 min after clamping and then decreased. However, 3-deoxyaldonic acids of 3-deoxytetronic acid, 3-deoxy-2-C-hydroxymethyltetronic acid and 3-deoxypentonic acid decreased in the renal tissue biopsy from 2 min after clamping.     

Microfluidic integration of substantially round glass capillaries for lateral patch clamping on chip

High-throughput screening of drug candidates for channelopathies can greatly benefit from an automated patch-clamping assay. Automation of the patch clamping through microfluidics ideally requires on-chip integration of glass capillaries with substantially round cross section. Such round capillaries, if they can only be integrated to connect isolated reservoirs on a substrate surface, will lead to a "lateral" configuration which is simple yet powerful for the patch clamping. We demonstrate here "lateral" patch clamping through microfluidic integration of substantially round glass capillaries in a novel process. The process adopts two well-known phenomena from microelectronics: keyhole-void formation and thermal-reflow of phosphosilicate glass in silicon trenches. The process relies on the same physical principle as the preparation of conventional micropipette electrodes by heat-pulling and fire-polishing glass tubes. The optimized process forms capillaries with a diameter approximately 1.5 microm and variation <10%. Functionality of the integrated glass capillaries for the patch-clamp recording has been verified by statistical test results from a sample of one hundred capillaries on mammalian cells (RBL-1) in suspension: 61% formed gigaseals (>1 GOmega) and of those approximately 48% (29% of all) achieved whole-cell recordings. Pharmacological blockade of ion channel activity and longevity of a whole-cell mode on these capillaries have also been presented.     

Review: Dielectrophoresis in cell characterization

Many cellular functions are affected by and thus can be characterized by a cell's electrophysiology. This has also been found to correspond to other biophysical parameters such as cell morphology and mechanical properties. Dielectrophoresis (DEP) is an electrostatic technique which can be used to examine cellular biophysical parameters through the measuring of single or multiple cell response to electric field induced forces. This label-free method offers many advantages in characterizing a cell population over conventional electrophysiology methods such as patch clamping; however, it has yet to see mainstream pharmacological application. Challenges such as the transdisciplinary nature of the field bridging engineering and the biological sciences, throughput, specificity as well as standardization are being addressed in current literature. This review focuses on the developments of DEP-based cell electrophysiological characterization where determining cellular properties such as membrane conductance and capacitance, and cytoplasmic conductivity are the primary motivation. A brief theoretical review, techniques for obtaining these cell parameters, as well as the resulting cell parameters and their applications are included in this review. This review aims to further support the development of DEP-based cell characterization as an important part of the future of DEP and electrophysiology research.     

Modified V-notched rail shear test fixture for shear characterisation of textile-reinforced composite materials

The V-notched rail shear test (VNRS) is recognised as a standard test method for the determination of shear modulus and shear strength of fibre-reinforced composite materials. This method is based on a double V-notched specimen with a large gauge section and an approximately uniform shear stress distribution between the two notches. The construction of the test device prescribed in standards was revised with the main focus of lines of force as well as precise and economic specimen clamping. Therefore, the modified test fixture has been equipped with guide units and the number of clamping bolts could be reduced. The standardised and modified VNRS fixtures were evaluated using a finite element method. It can be shown that the modified VNRS test fixture is well suited for robust and reliable material characterisation of shear property data.     

A simple technique to measure regional cerebral blood flow during intravascular balloon clamping

A case of giant internal carotid ophthalmic aneurysm was presented. In order to clarify whether the patient could tolerate carotid occlusion, a balloon clamping test was performed. before surgery. The cerebral blood flow was measured using early imaging by single photon emission computed tomography (SPECT) with N-isopropyl-(iodine-123)-p-iodoamphetamine (123I-IMP). When the balloon clamping test was performed the tracer was injected, and scanning was performed 35 minutes after removing the catheter. This tracer enabled a "memory of blood flow" during temporary ischemia to determine the character of quick diffusion and slow wash out, that could not be performed by other methods of cerebral blood flow measurement. SPECT with 123I-IMP can simplify the measurement of cerebral blood flow during the balloon clamping test.     

Compliance switching for adhesion control

Climbing lizards display numerous advanced features in their locomotion, notably a method to quickly switch between a state of low and high adhesive force capacity. Inspired by the gecko's adhesive switching, a method of mechanically switching between low and high adhesive states is reported. In particular, the first switching of an adhesive system using only a change in system compliance is demonstrated. Mechanical clamping and a novel magnetic clamping system are used to switch an iron/PDMS composite adhesive between a soft and rigid state. The switch in compliance directly influences the maximum load of the adhesive as measured in lap‐shear. Notably, contact area and the contact chemistry remain unaltered despite significant changes in force capacity. The demonstration of a compliance‐only switching mechanism has broad implications for understanding natural adhesive systems—especially in organisms that can dynamically alter their rigidity (e.g. cells). © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 48–57     

Quantitative analysis of polymers by attenuated total reflectance fourier-transform infrared spectroscopy: Vinyl acetate and methyl content of polyethylenes

A comparison was made between the transmission and attenuated total reflectance (ATR) infrared spectroscopic techniques for the determination of the vinyl acetate content of poly(ethylene–vinyl acetate) copolymers and methyl content of polyethylene. It was demonstrated that the transmission and ATR calibration curves for ratios of absorbances of bands with maxima at very similar wavelength were coincident, while those for ratios of absorbances of bands with maxima at significantly dissimilar wavelength were shifted apart. The explanation of this behavior is based on the wavelength dependence of the interaction of the IR radiation in ATR, compared to the wavelength independence of the interaction in transmission IR. The effect of polarized radiation was investigated in each type of analysis with the ATR technique. It was found that essentially the same results were obtained with the IR radiation polarized at 0° or 90°, relative to the plane of incidence, as compared to spectra obtained with unpolarized radiation. However, larger scatter was observed with polarized radiation. The effect of clamping pressure was also investigated. It was found that a minimum clamping torque of 5 in. lb is necessary to assure good physical contact in ATR work.     

Survival and extinction of delocalized ring currents in clamped benzenes

Direct visualisation of induced current density in clamped benzenes 1-4 distinguishes between saturated clamping groups, for which the central benzene ring retains a conventional diamagnetic ring current, and strongly interacting, unsaturated clamps, for which the central ring supports only the localised circulations expected of a 1,3,5-cyclohexatriene with fully fixed double bonds.     

Thermal stress development of liquid silicone rubber seal under temperature cycling

Liquid Silicone Rubber (LSR) is commonly used as gasket or seal material in many industrial applications. The temperature dependent material property of polymeric rubbers will result in stress relaxation/creep. The development of compressive stress in LSR between two clamping metal plates under temperature cycling is discussed in this paper. It is found that (a) in addition to stress relaxation, thermal expansion or contraction of the material contributes the most in the observed stress variation during temperature change, and (b) the stiffness of LSR appears to change according to temperature history.     

Modelisation du transfert de contrainte dans les materiaux composites ceramiques a fibres continues a partir d'essais de microindentation instrumentee. cas du materiau composite hi-nicalon/bn/α-si3n4

Microindentation tests have been used for analyzing the interfacial behaviour in HiNicalon/BN/Silicon nitride composites. When varying the maximum applied load and considering a constant interfacial shear stress, there was evidence of a Poisson's effect. A model, based on a Coulomb's law of friction, has been proposed to derive frictional stress values adjusted for the contribution of the expansion of the fibre. The advantages of this model are the explicit integration of all contributions to the clamping stress as well as the use of the experiment-based estimate of the roughness amplitude of Hi-Nicalon fibres.     

Analysis of a reversible five-point bending configuration based on a novel two-sense support

A novel two-sense support for flexural tests has been designed and manufactured in Ikerlan. The aim of this support is to do two-sense bending fatigue tests. In order to reduce the displacement corresponding to a given stress, a novel test configuration, designated as five-point bending, is modelled analytically. Basically, it is a three-point configuration with two supports at the ends that exert forces in the same sense as the applied load. In this way, a partial clamping is obtained that can be modelled by concentrated loads. The model has been checked carrying out quasi-static three-point and five-point bending tests at different spans in unidirectional carbon/epoxy composite specimens. Flexural modulus and the out-of-plane shear modulus have been obtained by linear regression in both cases, after having obtained experimentally the stiffness of the system.     

Which pi-clamped conjugated monocycles exhibit ring currents?

Quenching/survival of ring currents in pi-clamped conjugated monocycles is controlled by the match or mismatch in parity between the frontier orbitals of the central pi-conjugated 4n+2/4n monocycle and those of the clamps. Changes in ring current are not primarily caused by bond alternation or 'Mills-Nixon' effects; current and geometry changes on clamping are both consequences of electronic structure.     

Mechanochemical reactions in an epoxy resin system

Mechanical degradation of the MY720/Eporal (CIBA GEIGY) epoxy resin system was investigated by stress mass spectrometry. Resin coupons were strained to fracture in a unique mass spectrometer system in which the clamping jaws of an Instron tensile tester are located inside the ion-source housing of a time-of-flight mass spectrometer. Several compounds are released at the instant of fracture. However, only one compound, SO₂, is not an impurity in either the starting material or the cured resin. A sensitive gas-chromatographic technique was used to search for SO₂ indigenous to the starting material and the unstressed cured resin. The data indicate that SO₂ is a mechanochemical reaction product generated during main-chain bond cleavage of the glassy epoxy resin network.     

Structure-activity relationships, kinetics, selectivity, and mechanistic studies of synthetic hydraphile channels in bacterial and mammalian cells

Hydraphile compounds are shown to be cytotoxic to Gram-negative and Gram-positive bacteria, yeast, and mammalian cells. Their cellular toxicity compares favorably with other synthetic ionophores and rivals that potency of natural antibiotics. The effects of structural variations on toxicity are described. The effects of these variations correlate well with previous studies of ion transport in liposomes. Whole cell patch clamping with mammalian cells confirms a channel mechanism in living cells suggesting that this family may comprise novel and flexible pharmacological agents.     

Reaction path potential for complex systems derived from combined ab initio quantum mechanical and molecular mechanical calculations

Combined ab initio quantum mechanical and molecular mechanical calculations have been widely used for modeling chemical reactions in complex systems such as enzymes, with most applications being based on the determination of a minimum energy path connecting the reactant through the transition state to the product in the enzyme environment. However, statistical mechanics sampling and reaction dynamics calculations with a combined ab initio quantum mechanical (QM) and molecular mechanical (MM) potential are still not feasible because of the computational costs associated mainly with the ab initio quantum mechanical calculations for the QM subsystem. To address this issue, a reaction path potential energy surface is developed here for statistical mechanics and dynamics simulation of chemical reactions in enzymes and other complex systems. The reaction path potential follows the ideas from the reaction path Hamiltonian of Miller, Handy and Adams for gas phase chemical reactions but is designed specifically for large systems that are described with combined ab initio quantum mechanical and molecular mechanical methods. The reaction path potential is an analytical energy expression of the combined quantum mechanical and molecular mechanical potential energy along the minimum energy path. An expansion around the minimum energy path is made in both the nuclear and the electronic degrees of freedom for the QM subsystem internal energy, while the energy of the subsystem described with MM remains unchanged from that in the combined quantum mechanical and molecular mechanical expression and the electrostatic interaction between the QM and MM subsystems is described as the interaction of the MM charges with the QM charges. The QM charges are polarizable in response to the changes in both the MM and the QM degrees of freedom through a new response kernel developed in the present work. The input data for constructing the reaction path potential are energies, vibrational frequencies, and electron density response properties of the QM subsystem along the minimum energy path, all of which can be obtained from the combined quantum mechanical and molecular mechanical calculations. Once constructed, it costs much less for its evaluation. Thus, the reaction path potential provides a potential energy surface for rigorous statistical mechanics and reaction dynamics calculations of complex systems. As an example, the method is applied to the statistical mechanical calculations for the potential of mean force of the chemical reaction in triosephosphate isomerase.