Large Tip Diameter Research Articles

Nanopore Probes Using Hydrogel-Filled Nanopipettes as Sensors for Chemical Imaging

Scanning ion conductance microscopy (SICM) using biological nanopores is a powerful analytical tool that can provide spatially resolved topography and chemical information. However, the low spatial resolution caused by the large tip diameter of the probe has limited the practical application of the SICM system. Although the tip-dip method has conventionally been used to form a lipid bilayer at the tip of pipettes, an alternative method to form the lipid bilayer is required because the lifetime of lipid bilayers formed by the tip-dip method is too short to map chemical information by stochastic nanopore sensing. Here, we propose a method to prepare lipid bilayers using a hydrogel-filled nanopipette. The lipid bilayer is formed at the tip of the pipette by inserting the pipette into a layered solution of an oil/lipid mixture and an aqueous electrolyte. Since the hydrogel supports the lipid bilayer, the lifetime of the lipid bilayers prepared by this method is improved over that formed by the tip-dip method. Furthermore, the hydrogel at the pore aperture reduces the translocation speed of analytes through nanopores, indicating that the hydrogel-filled nanopipette system can offer highly sensitive chemical sensing. Finally, we measure local single-strand deoxyribonucleic acid concentrations in the concentration gradient generated by a microhole using the biological nanopore probe. We believe that the SICM system using the hydrogel-filled nanopipette-based biological nanopore probe will offer a powerful analytical system for biological phenomena, including cell communication and signal transduction.

Suction-Controlled Detachment of Mushroom-Shaped Adhesive Structures

Abstract Experimental evidence suggests that suction may play a role in the attachment strength of mushroom-tipped adhesive structures, but the system parameters which control this effect are not well established. A fracture mechanics-based model is introduced to determine the critical stress for defect propagation at the interface in the presence of trapped air. These results are compared with an experimental investigation of millimeter-scale elastomeric structures. These structures are found to exhibit a greater increase in strength due to suction than is typical in the literature, as they have a large tip diameter relative to the stalk. The model additionally provides insight into differences in expected behavior across the design space of mushroom-shaped structures. For example, the model reveals that the suction contribution is length-scale dependent. It is enhanced for larger structures due to increased volume change, and thus the attainment of lower pressures, inside of the defect. This scaling effect is shown to be less pronounced if the tip is made wider relative to the stalk. An asymptotic result is also provided in the limit that the defect is far outside of the stalk, showing that the critical stress is lower by a factor of 1/2 than the result often used in the literature to estimate the effect of suction. This discrepancy arises as the latter considers only the balance of remote stress and pressure inside the defect and neglects the influence of compressive tractions outside of the defect.

Effect of surface tension, viscosity, pore geometry and pore contact angle on effective pore throat

Through experimental measurement and theoretical calculation, we have investigated the effect of surface tension, liquid viscosity and the capillary geometry (capillary gradient and tip diameter) on the effective pore throat, and the impact of the effective pore throat on pore resistance to two-phase interfaces formed from fluids with different viscosities and surface tensions. When a two-phase interface flows in channels with varied pore diameter, capillary force is insignificant in the section of the channel with an inner pore diameter greater than the effective pore throat, and the pressure drops in this section depend on capillary tip diameter, rather than the surface tension. Capillary force takes significant effect on the interface only when the pore diameter in a tapered capillary is smaller than the effective pore throat. Effective pore throat depends on fluid surface tension and the capillary geometry, but not on liquid viscosity. The higher the fluid surface tension, the larger the diameter of the effective pore throat. A channel with a large tip diameter or gradient will give a large effective pore throat diameter. Fluid viscosity only affects the magnitude of the resistant pressure drops of fluid flows in constricted capillaries, but does not affect the effective pore throat diameter. The effective pore throat and the pressure profile measured in this study can be explained by the pore contact angle, but cannot be explained by the contact angle on a flat surface of the same materials.

Fan Similarity Model for the Fan–Intake Interaction Problem

Very high bypass ratio turbofans with large fan tip diameter are an effective way of improving the propulsive efficiency of civil aero-engines. Such engines, however, require larger and heavier nacelles, which partially offset any gains in specific fuel consumptions. This drawback can be mitigated by adopting thinner walls for the nacelle and by shortening the intake section. This binds the success of very high bypass ratio technologies to the problem of designing an intake with thin lips and short diffuser section, which is well matched to a low speed fan. Consequently, the prediction of the mutual influence between the fan and the intake flow represents a crucial step in the design process. Considerable effort has been devoted in recent years to the study of models for the effects of the fan on the lip stall characteristics and the operability of the whole installation. The study of such models is motivated by the wish to avoid the costs incurred by full, three-dimensional (3D) computational fluid dynamics (CFD) computations. The present contribution documents a fan model for fan–intake computations based on the solution of the double linearization problem for unsteady, transonic flow past a cascade of aerofoils with finite mean load. The computation of the flow in the intake is reduced to a steady problem, whereas the computation of the flow in the fan is reduced to one steady problem and a set of solutions of the linearized model in the frequency domain. The nature of the approximations introduced in the fan representation is such that numerical solutions can be computed inexpensively, while the main feature of the flow in the fan passage, namely the shock system and an approximation of the unsteady flow encountered by the fan are retained. The model is applied to a well-documented test case and compares favorably with much more expensive 3D, time-domain computations.

Modelling and parametric analysis of small-scale axial and radial-outflow turbines for Organic Rankine Cycle applications

The existing literature pays limited attention to the design and 3D analysis of small-scale axial and radial–outflow turbines that can be utilised in Organic Rankine Cycles (ORC) for power generation with a low–temperature (<100°C) heat source and low mass flow rate. Turbine efficiency significantly affects an ORC’s efficiency because the turbine is considered a key component of the ORC. Therefore, obtaining high cycle thermal efficiency requires high turbine efficiency and power output. This work presents an integrated mathematical model for developing efficient axial and radial-outflow (centrifugal) turbines using a range of organic working fluids (R141b, R245fa, R365mfc, isobutane and n–pentane). This mathematical approach integrates mean-line design and 3D CFD analysis with ORC modelling. The ANSYSR17CFX is used to predict 3D viscous flow and turbine performance. To achieve accurate prediction, the ORC/turbines model uses real gas formulations based on the REFPROP database. The results showed that the axial turbine performed better, with efficiency of 82.5% and power output of 15.15kW, compared with 79.05% and 13.625kW from the radial–outflow turbine, with n-pentane as the working fluid in both cases. The maximum cycle thermal efficiency was 11.74% and 10.25% for axial and radial-outflow turbines respectively with n-pentane as the working fluid and a heat source temperature of 87°C. The large tip diameter of the axial turbine was 73.82mm compared with 108.72mm for the radial-outflow turbine. The predicted results are better than others in the literature and highlight the advantages of the integrated approach for accurate prediction of ORC performance based on small-scale axial and radial-outflow turbines.

Differences in sensitivity to microstructure between cyclic- and impact-based microindentation of human cortical bone.

Unlike the known relationships between traditional mechanical properties and microstructural features of bone, the factors that influence the mechanical resistance of bone to cyclic reference point microindention (cRPI) and impact microindention (IMI) have yet to be identified. To determine whether cRPI and IMI properties depend on microstructure, we indented the tibia mid-shaft, the distal radius, and the proximal humerus from 10 elderly donors using the BioDent and OsteoProbe (neighboring sites). As the only output measure of IMI, bone material strength index (BMSi) was significantly different across all three anatomical sites being highest for the tibia mid-shaft and lowest for the proximal humerus. Total indentation distance (inverse of BMSi) was higher for the proximal humerus than for the tibia mid-shaft but was not different between other anatomical comparisons. As a possible explanation for the differences in BMSi, pore water, as determined by 1 H nuclear magnetic resonance, was lowest for the tibia and highest for the humerus. Moreover, the local intra-cortical porosity, as determined by micro-computed tomography, was negatively correlated with BMSi for both arm bones. BMSi was also positively correlated with peak bending stress of cortical bone extracted from the tibia mid-shaft. Microstructural correlations with cRPI properties were not significant for any of the bones. The one exception was that average energy dissipated during cRPI was negatively correlated with local tissue mineral density in the tibia mid-shaft. With higher indentation force and larger tip diameter than cRPI, only IMI appears to be sensitive to the underlying porosity of cortical bone. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1442-1452, 2017.

Mushroom-Shaped Micropillars for Robust Nonwetting Surface by Electrohydrodynamic Structuring Technique

Mushroom-shaped micropillars (MSMPs) have a unique microscopic shape that is suitable to produce a highly robust nonwetting surface. This commercially important property is possible thanks to the specific overhang shape, which has a larger tip diameter than the shaft below. We fabricated such a textured surface using poly(methyl methacrylate) (PMMA) via electrohydrodynamic structuring technique. The method combines hot embossing, electrically induced growth, and electrowetting. Even though PMMA itself is hydrophilic (the intrinsic contact angle is 82°), its modified surface is hydrophobic with an apparent contact angle of 152°. We also studied the robustness of the nonwetting surface by comparing the difference between the static contact angles before and after the samples had been submerged in water. Our results show that only the surface structured with the 43-μm tip-diameter MSMPs (the largest size) can successfully maintain its highly nonwetting property. Because of the large fabrication potential of the MSMPs with a large tip diameter, the described surface structuring technique is a promising candidate for the mass production of artificial and sufficiently robust nonwetting surfaces.

Biomimetic mushroom-shaped microfibers for dry adhesives by electrically induced polymer deformation.

The studies on bioinspired dry adhesion have demonstrated the biomimetic importance of a surface arrayed with mushroom-shaped microfibers among other artificially textured surfaces. The generation of a mushroom-shaped microfiber array with a high aspect ratio and a large tip diameter remains to be investigated. In this paper we report a three-step process for producing mushroom-shaped microfibers with a well-controlled aspect ratio and tip diameter. First, a polymer film coated on an electrically conductive substrate is prestructured into a low-aspect-ratio micropillar array by hot embossing. In the second step, an electrical voltage is applied to an electrode pair composed of the substrate and another conductive planar plate, sandwiching an air clearance. The Maxwell force induced on the air-polymer interface by the electric field electrohydrodynamically pulls the preformed micropillars upward to contact the upper electrode. Finally, the micropillars spread transversely on this electrode due to the electrowetting effect, forming the mushroom tip. In this paper we have demonstrated a polymer surface arrayed with mushroom-shaped microfibers with a large tip diameter (3 times the shaft diameter) and a large aspect ratio (above 10) and provided the testing results for dry adhesion.

Morphological Dilation as Fractal Scaling in Roughness Measurement

In this work we propose, that the morphological dilation acts as fractal filters rebuilding white noise roughness surfaces into fractal 1/fm noise surfaces. The fractality indicates that the dilation does not have characteristic length scale, and the structuring element follows power-law distribution. Yashchuk's binary pseudo-random grating standard has been dilated with spherical and free form tips between 50 nm and 2000 nm and two scaling regions are referred to the tip diameter versus scaling exponent diagram. The first one in the smaller tip diameter region has a fast slope and the second one in the intermediate and larger tip diameter has a gradual slope. The results show that the dilated surfaces arise from the activity of at least two dynamical systems.

Deep brain pulse‐generator and lead‐extensions: Subjective sensations related to measured parameters

This study analyzed subjective sensations caused by DBS pulse-generator and lead-extensions in relation with objectively measured parameters. In 50 patients implant-related sensations were evaluated. The pulse-generator mobility was video-analyzed. Insufficient lead-extension/pulse-generator tolerability (72%/84%) was documented. Furthermore, 54% of the patients described movement impairments and 48% cosmetic deformity. High body mass index (BMI) was associated with low lead-extension related pain (P < 0.001). High generator mobility resulted in high lead-extension related pain (P < 0.001). Compared with lead-extension type 7482, type 7495 showed less lead-extension related pain (P = 0.0138), we suppose secondary to surgical tunneling instruments with a larger tip diameter. The lead-extension path with one tissue tunnel for both lead-extensions had 36% lead-extension related pain versus 11% for the path with one single tunnel for each lead-extension. Smaller pulse-generators for better cosmetic results, surgical procedures using larger tunneling instruments and one single tunnel for each lead-extension would provide better results for patients with BMI <30.

Macroscopic K+ currents in single smooth muscle cells of the rabbit portal vein.

1. Single smooth muscle cells isolated from rabbit portal vein were voltage clamped at room temperature using the whole-cell configuration of the patch-clamp technique. These cells exhibited a mean resting potential of -47.9 mV and a mean input resistance of 376 M omega. 2. Using small tip diameter micropipettes (to avoid dialysis of the cells), depolarizing voltage-clamp pulses from a holding potential of -50 mV elicited two distinct outward currents: a quasi-instantaneous background current and a time-dependent current that did not appear to inactivate (delayed rectifier). Upon return to the holding potential, an outward tail current decaying back to the holding current was observed. 3. The time course of development of the tail current as estimated from envelopes of tail current protocols followed the kinetics of activation of the delayed rectifier elicited during the preceding test pulse. The tail current reversed close to the equilibrium potential for K+ ions indicating that it is mainly carried by potassium ions. 4. Using large tip diameter micropipettes to internally dialyse the cells (EGTA = 0.1 mM; ATP = 5 mM), two additional outward currents having transient kinetics were revealed: a smooth transient outward current (Ito) and spontaneous transient outward currents (STOCs). Ito was found to be mainly selective for K+ ions and exhibited voltage-dependent inactivation with half-maximal availability near -40 mV. 5. Removal of calcium from the bathing solution significantly reduced the background current and abolished both Ito and STOCs. The delayed rectifier current appeared to be insensitive to this procedure. The two types of transient outward currents were never recorded when EGTA was elevated to 5 mM inside the micropipette whereas the background and delayed rectifier currents were not affected. These results suggested that Ito and the spontaneous transient outward currents are activated by internal calcium. 6. External application of TEA (0.5-20 mM) blocked all four outward currents. Calcium replacement by barium significantly reduced the background current and Ito, and had small effects on the delayed rectifier current. When potassium was replaced with caesium (130 mM) and TEA (20 mM) inside the pipette, none of the outward currents described was ever observed. In about 60% of the cells dialysed with this solution a small inward Ca2+ current was revealed. 7. External application of caffeine (5 mM) abolished STOCs in cells in which this activity was present under control conditions. In cells lacking this type of activity under control conditions caffeine induced and later abolished this type of current.(ABSTRACT TRUNCATED AT 400 WORDS)

Scanning Electron Microscopy Studies of Tear of Carboxylated Nitrile Rubber

Abstract Mechanism of tear of unfilled and carbon black filled carboxylated nitrile rubber (XNBR) having metallocarboxylate crosslinks, sulfur-sulfur crosslinks and mixed type crosslinking systems has been studied by Scanning Electron Microscope. Tear proceeds through stick-slip process in the case of gum mixes. The number of tear lines is more in the sulfur crosslinked system, resulting in poor tear strength. Addition of reinforcing carbon black changes the mechanism of tear. The sulfur crosslinked system shows knotty tear, while introduction of ionic crosslinks results in smooth tear presumably due to the large tip diameter reaching the edge of the specimen.

The physics of iontophoretic pipettes

A theoretical study has been made of the release of drugs from iontophoretic pipettes. The chief predictions are: (1) in the steady state, release becomes linear with current and independent of pipette geometry when the ejecting voltage exceeds approximately 100 mV; (2) release rises relatively slowly during an ejecting pulse to approach its steady state value. At the end of the pulse, release falls abruptly. This asymmetry of the release curve is greatly accentuated by the prior application of a retaining current. It provides an explanation for the characteristic time course of response commonly seen when drugs are applied iontophoretically to central neurones; (3) the above effects occur on a time scale which depends strongly on the geometry of the pipette. Release from pipettes of large tip diameter and nearly cylindrical bore, such as those generally used in the central nervous system, should be thousands of times slower than from pipettes of small tip diameter and large taper angle. Experimental observations of the release of an ionized fluorescent compound quantitatively confirm prediction (1) and qualitatively confirm predictions (2) and (3).