Tip Geometry Research Articles

Assessment of needle tip geometry during infusions into a brain phantom gel

Convection-enhanced delivery (CED) is a promising method to deliver therapeutic drugs directly into the brain that has shown limited efficacy, mainly attributed to backflow, in which the infused drug flows back along the needle track rather than forward into tissue. This study evaluates the effect of sharp and blunt needle tips on backflow length under different flow rates via CED. Infusions were performed in a transparent 0.6% (w/v) brain phantom agarose hydrogel. Backflow length was significantly higher using sharp-tip needles for higher flow rates. No significant differences were observed between tip shapes for lower flow rates. In conclusion, sharp-tip needles present limitations for higher flow rates, which are needed to deliver more drug during shortest times.

Intraspinal stimulation with a silicon-based 3D chronic microelectrode array for bladder voiding in cats

Objective. Bladder dysfunction is a significant and largely unaddressed problem for people living with spinal cord injury (SCI). Intermittent catheterization does not provide volitional control of micturition and has numerous side effects. Targeted electrical microstimulation of the spinal cord has been previously explored for restoring such volitional control in the animal model of experimental SCI. Here, we continue the development of the intraspinal microstimulation array technology to evaluate its ability to provide more focused and reliable bladder control in the feline animal model. Approach. For the first time, a mechanically robust intraspinal multisite silicon array was built using novel microfabrication processes to provide custom-designed tip geometry and 3D electrode distribution. Long-term implantation was performed in eight spinally intact animals for a period up to 6 months, targeting the dorsal gray commissure area in the S2 sacral cord that is known to be involved in the coordination between the bladder detrusor and the external urethral sphincter. Main results. About one third of the electrode sites in the that area produced micturition-related responses. The effectiveness of stimulation was further evaluated in one of eight animals after spinal cord transection (SCT). We observed increased bladder responsiveness to stimulation starting at 1 month post-transection, possibly due to supraspinal disinhibition of the spinal circuitry and/or hypertrophy and hyperexcitability of the spinal bladder afferents. Significance. 3D intraspinal microstimulation arrays can be chronically implanted and provide a beneficial effect on the bladder voiding in the intact spinal cord and after SCT. However, further studies are required to assess longer-term reliability and safety of the developed intraspinal microstimulation array prior to eventual human translation.

Laser Sharpening of Carbon Fiber Microelectrode Arrays for Brain Recording.

Microwire microelectrode arrays (MEAs) are implanted in the brain for recording neuron activities to study the brain function. Among various microwire materials, carbon fiber stands out due to its small diameter (5-10 μm), relatively high Young's modulus, and low electrical resistance. Microwire tips in MEAs are often sharpened to reduce the insertion force and prevent the thin microwires from buckling. Currently, carbon fiber MEAs are sharpened by either torch burning, which limits the positions of wire tips to a water bath surface plane, or electrical discharge machining, which is difficult to implement to the nonelectrically conductive carbon fiber with parylene-C insulation. A laser-based carbon fiber sharpening method proposed in this study enables the fabrication of carbon fiber MEAs with sharp tips and custom lengths. Experiments were conducted to study effects of laser input voltage and transverse speed on carbon fiber tip geometry. Results of the tip sharpness and stripped length of the insulation as well as the electrochemical impedance spectroscopy measurement at 1 kHz were evaluated and analyzed. The laser input voltage and traverse speed have demonstrated to be critical for the sharp tip, short stripped length, and low electrical impedance of the carbon fiber electrode for brain recording MEAs. A carbon fiber MEA with custom electrode lengths was fabricated to validate the laser-based approach.

Direct observation of partial interface slip in micrometre-scale single asperity contacts

Observation of partial interface slip prior to sliding is reported in micrometre-scale single asperity contacts formed of diamond tips and various substrate materials. Using a dual-axis nanoindenter, an increasing oscillating lateral load is applied to contacts indented under constant normal load. Lateral load-displacement curves are extracted, with partial slip signalled by a steady decrease in contact stiffness as the magnitude of oscillation increases, dropping to zero during sliding. Both elastic and plastic contacts are examined, and contact radii from 215 to 485 nm. An interfacial strength τ0 is measured, which appears independent of radius, tip geometry, and elastic/plastic state of the substrate. This behaviour is observed in both amorphous silica and single crystal quartz contacts and a significant friction anisotropy in sapphire is demonstrated.

Impact of multiple type of tool TIP geometry on various features of a magnesium based alloy AZ91A by abrasion stir welding

In Abrasion Stir Welding instrument break quality expects a vital part in the midst of gadget jump and withstand. The close by nerves and damage conveyed upon the instrument contacts the work job is sufficient to rupture a gadget. Along these lines the material of the mechanical assembly used for crushing mix welding should have high break solidness. The surface effects within the gadget get different if the device reacts within the work job or the earth. Magnesium is most likely comprehended with its reaction on raised thermal degree and reaction of magnesium with the device substances will differ the gadget property. As needs required matter of the gadget is picked within a way that it should not react with work job or the earth to keep up its personal effects. In the occasion that sticks & shoulder substances have a colossal complexity in degree of warm augmentation which also prompts improvement of the shoulder regarding stick or expansion of tip in regard to manage. Between two of the conditions there’s an extension in the nerves between the tin and shoulder which can incite dissatisfaction of the gadget. Gadgets include a shoulder and a test which can be essential with the shoulder or as an alternate install maybe of a substitute material. The design of the shoulder & that of the test is basic for the idea of the weld.

Influence of different tool tip geometry on parameters of magnesium based alloy AZ91A by abrasion stir welding

Abrasion Stir Welding is a solid state process, which suggests that the things are fixed prior accomplishing the melting degree. An incredible grade pounding blend weld uses a genuine mechanical assembly material decision with the looked for application. Most scouring blend gadgets have features that are looked for specific limits. The gadget substances used with grinding mix welds should have taking after traits if the instrument erosion is over the top, it changed the condition of the gadget thus changed in the weld grading also the probability of flaws is similarly extended. In the midst of granulating blend welding process mechanical assembly erosion can occur by concrete, grinding or manufactured wear frameworks.

Fabrication of Silicon Microtips with Integrated Electrodes

This paper describes a simple method to fabricate silicon microtips with integrated self-aligned polarization electrodes for development of MEMS and electron field emission devices. The method is based on the wet bulk micromachining of the silicon substrate in KOH solutions and utilizes low stress PECVD SiOxNy films obtained at low temperatures (320°C) as structural material for both mechanical support and electrical insulation of the electrodes. For the electrodes sputtered Cr films were utilized. The microtip formation process was studied by optical and electronic microscopy to analyze tip geometry and the characteristic etch rate of the different stages during the tips formation. The fabricated devices were matrixes with different numbers of microtips, each with a typical height of 52 μm and with diameter at the apex below 1 μm. In the best case, the distance between the apex of the tips and the metallic electrode was lower than 5 μm. The results also show that the low stress SiOxNy film is essential to attain the necessary flatness required by the process.

Nanoscale terahertz STM imaging of a metal surface

Terahertz scanning tunneling microscopy (THz-STM) has enabled studies of ultrafast dynamics in materials down to the atomic scale. However, despite recent advances, more work is needed to better understand and quantify the subpicosecond THz pulse-induced tunnel currents and corresponding THz-STM images of nanoscale features on surfaces. Here, we perform THz-STM on a metal surface and fully characterize the observed THz pulse-induced tunnel current and nanoscale imaging at atomic steps and defects using a Bardeen tunneling model in a three-dimensional (3D) tip geometry. We show that the measured steady-state STM current-voltage curves can be used in our model to accurately map the observed ultrafast THz-induced tunnel currents and calibrate the magnitude of the near-field peak transient THz voltage bias in the tunnel junction. Peak THz voltage bias transients greater than 10 V across the STM junction are achieved leading to field emission of subpicosecond tunnel currents with current densities exceeding ${10}^{9}\phantom{\rule{0.28em}{0ex}}\mathrm{A}/\mathrm{c}{\mathrm{m}}^{2}$ in THz-STM imaging of a Cu(111) surface. Our results establish an important benchmark for future studies in THz-STM by quantifying the ultrafast THz-induced currents and bias voltages in the tunnel junction and providing a 3D tunneling model for understanding and accurately simulating THz-STM images of nanoscale features on metal surfaces.

Rupture of Liquid Bridges on Porous Tips: Competing Mechanisms of Spontaneous Imbibition and Stretching.

Liquid bridges are commonly encountered in nature and the liquid transfer induced by their rupture is widely used in various industrial applications. In this work, with the focus on the porous tip, we studied the impacts of capillary effects on the liquid transfer induced by the rupture through numerical simulations. To depict the capillary effects of a porous tip, a time scale ratio, RT, is proposed to compare the competing mechanisms of spontaneous imbibition and external drag. In terms of RT, we then develop a theoretical model for estimating the liquid retention ratio considering the geometry, porosity, and wettability of tips. The mechanism presented in this work provides a possible approach to control the liquid transfer with better accuracy in microfluidics or microfabrications.

Expulsion Intensity Monitoring and Modeling in Resistance Spot Welding Based on Electrode Displacement Signals

Abstract Weld expulsion is one of the most common welding defects during the resistance spot welding (RSW) process, especially for high strength steels (HSS). In order to control and eventually eliminate weld expulsion in production, accurate assessment of the expulsion severity should be the first step and is urgently required. Among the existing methods, real-time monitoring of RSW-related process signals has become a promising approach to actualize the online evaluation of weld expulsion. However, the inherent correlation between the process signals and the expulsion intensity is still unclear. In this work, a commonly used process signal, namely, the electrode displacement and its instantaneous behavior when expulsion occurs are systematically studied. Based upon experiments with various electrodes and workpieces, a nonlinear correlation between the weight of expelled metal and the sudden displacement drop accompanied by the occurrence of weld expulsion is observed, which is mainly influenced by electrode tip geometry but not by material strength or sheet thickness. The intrinsic relationship between this specific signal feature and the magnitude of expulsion is further explored through geometrical analysis, and a modified analytical model for online expulsion evaluation is finally proposed. It is shown that the improved model could be applied to domed electrodes with different tip geometries and varying workpieces ranging from low carbon steel to HSS. The error of expulsion estimation could be limited within ±20.4 mg (±2σ) at a 95% confidence level. This study may contribute to the online control of weld expulsion to the minimum level.

Сравнительный анализ сил, действующих на поглощающий элемент системы управления и защиты в потоке вязкой несжимаемой жидкости, в зависимости от геометрии наконечника стержня и диаметра направляющего канала

Сравнительный анализ сил, действующих на поглощающий элемент системы управления и защиты в потоке вязкой несжимаемой жидкости, в зависимости от геометрии наконечника стержня и диаметра направляющего канала

Cone-Paraboloid Transition of the Johnson-Kendall-Roberts-Type Hyperboloidal Contact.

Atomic force microscopy (AFM)-based nanoindentation technique has been widely used to investigate the mechanical properties of compliant specimens. When a sharp probe is indented into a soft and adhesive specimen, not only the rounded end of the probe but also the pyramidal base may be in contact. However, even in such a case, a contact model that assumes a paraboloidal tip geometry (the Hertz model or one of its expansions) is mainly employed to derive the mechanical properties; the error on the mechanical properties induced by the inaccurate tip geometry assumption has not been systematically clarified. Therefore, the focus of this work was put on quantifying this error with the assumption that the actual contact occurs between a hyperboloidal indenter and an elastic and adhesive sample surface. We demonstrated that the cone-paraboloid transition of the indentation curve is governed by a single parameter, A̅ = [4RE/3πw(1 - ν2)]1/3cotα, where E and ν are Young's modulus and Poisson's ratio of the specimen, respectively, R and α are the curvature radius and half-angle of the indenter, respectively, and w is the work of adhesion. Employing the general two-point method, we quantified the errors on elasticity and surface energy caused by the assumption of the paraboloidal and conical Johnson-Kendall-Roberts (JKR) models as functions of A̅ and the normalized load. AFM force measurements with cantilevers of different radii supported this A̅ dependency. These results showed unsuitable geometry assumption can give a large error, which is generally more serious than those caused by inappropriate choice of the adhesive interaction from the JKR and DMT (Derjaguin-Muller-Toporov). It can be said that the conical model gives a good approximation to a hyperboloidal contact when A̅<1 and so does the paraboloidal model when A̅>4. A̅ is expected to be an important index that validates the paraboloidal and conical approximation in a soft and adhesive contact.

Nanovolcano microelectrode arrays: toward long-term on-demand registration of transmembrane action potentials by controlled electroporation

Volcano-shaped microelectrodes (nanovolcanoes) functionalized with nanopatterned self-assembled monolayers have recently been demonstrated to report cardiomyocyte action potentials after gaining spontaneous intracellular access. These nanovolcanoes exhibit recording characteristics similar to those of state-of-the-art micro-nanoelectrode arrays that use electroporation as an insertion mechanism. In this study, we investigated whether the use of electroporation improves the performance of nanovolcano arrays in terms of action potential amplitudes, recording durations, and yield. Experiments with neonatal rat cardiomyocyte monolayers grown on nanovolcano arrays demonstrated that electroporation pulses with characteristics derived from analytical models increased the efficiency of nanovolcano recordings, as they enabled multiple on-demand registration of intracellular action potentials with amplitudes as high as 62 mV and parallel recordings in up to ~76% of the available channels. The performance of nanovolcanoes showed no dependence on the presence of functionalized nanopatterns, indicating that the tip geometry itself is instrumental for establishing a tight seal at the cell–electrode interface, which ultimately determines the quality of recordings. Importantly, the use of electroporation permitted the recording of attenuated cardiomyocyte action potentials during consecutive days at identical sites, indicating that nanovolcano recordings are nondestructive and permit long-term on-demand recordings from excitable cardiac tissues. Apart from demonstrating that less complex manufacturing processes can be used for next-generation nanovolcano arrays, the finding that the devices are suitable for performing on-demand recordings of electrical activity from multiple sites of excitable cardiac tissues over extended periods of time opens the possibility of using the devices not only in basic research but also in the context of comprehensive drug testing.

Indenting soft samples (hydrogels and cells) with cantilevers possessing various shapes of probing tip

The identification of cancer-related changes in cells and tissues based on the measurements of elastic properties using atomic force microscopy (AFM) seems to be approaching clinical application. Several limiting aspects have already been discussed; however, still, no data have shown how specific AFM probe geometries are related to the biomechanical evaluation of cancer cells. Here, we analyze and compare the nanomechanical results of mechanically homogenous polyacrylamide gels and heterogeneous bladder cancer cells measured using AFM probes of various tip geometry, including symmetric and non-symmetric pyramids and a sphere. Our observations show large modulus variability aligned with both types of AFM probes used and with the internal structure of the cells. Altogether, these results demonstrate that it is possible to differentiate between compliant and rigid samples of kPa elasticity; however, simultaneously, they highlight the strong need for standardized protocols for AFM-based elasticity measurements if applied in clinical practice including the use of a single type of AFM cantilever.

Machine-learnt topology of complex tip geometries in gas turbine rotors

The work presents a data driven based strategy to develop a new statistical model of complex tip shape for high-pressure turbine stages exploiting an existing dataset of optimized squealer-like rotor tips. Using the exploratory data analysis (EDA), a set of statistical methods were used to improve the quality of previous CFD-based optimization dataset, as an aid in reducing outliers, data skewness and avoiding the presence of redundant information. The pre-processed dataset was analyzed by unsupervised learning method in order to gain insight on the correlation between tip geometry and single stage axial turbine performance. Utilizing the Principal Component Analysis (PCA), we developed a new continuous, dimensionality-reduced parametrization which allows overcoming the limitations of discrete topology approaches. The novel statistical shape model, coupled with genetic operators into a NSGA-II optimization strategy, was used to explore the design space of optimal solutions generating new designs to enrich the available Pareto front in terms of aero-thermodynamic performance metrics. Two metamodels for performance prediction, respectively based on Artificial Neural Network (ANN) and Gradient Boosting Regressor (GBR) have been developed in order to guide the Pareto front exploration avoiding the use of computationally intensive CFD simulations. New tip designs were carried out to spread the previous optimal front and, successively, aiming to design individuals able to reduce macroscopic not uniformity of the flow keeping optimal aerodynamic performance.

In-nozzle flow and spray characteristics of large two-stroke marine diesel fuel injectors

To further increase efficiency as well as to reduce emissions of large two-stroke marine Diesel engines, the understanding of the fuel injection processes and the resulting spray atomization characteristics is of high importance. The sheer dimensions, the uniflow scavenging design with the central exhaust valve position and the high swirl motion of the charge air is imposing the need for peripheral multiple fuel injector arrangement. The two or three fuel injectors are arranged by 180° resp. 120° and hence, a strongly asymmetrical and eccentrical atomizer design is given as all of the typically five orifices face a similar direction which is defined by the injector position and swirl flow. Experiments have shown that these characteristic nozzle tip bore arrangements lead to a strong spray deflection due to inhomogeneous velocity profiles induced by cavitation inside the orifice. Specifically designed transparent nozzles have been utilized to qualitatively investigate the in-nozzle cavitation flow phenomena. Furthermore, the influence on the subsequent atomization behaviour by simultaneously acquiring the spray morphology has been studied. A simplified transparent one-hole nozzle was used with a matching nozzle tip geometry representative for a large two-stroke marine Diesel engine injector. Fuel pressures of 50 MPa were applied to meet engine realistic injection conditions. Moreover, different degrees of hydro-erosive grinding were applied to the orifices to investigate the effects on the spray morphology with decreasing levels of in-nozzle flow cavitation derived by increasing inlet radii between main nozzle tip bore and orifice.

Application of Multiscale Methodology for Transonic Turbine Blade Tip Cooling Design

Abstract Recent research suggests that the cooling flow at transonic turbine tip has several unique flow features such as the strong interaction with the base flow, the acceleration at divergent duct, the strong shock boundary layer interaction, and the weak correlation between aerodynamic loss and the heat transfer. These flow features require the cooling design to be considered together with the tip geometry shaping. However, due to the large disparity of the length scales between the cooling holes and the turbine blade, the combination of the cooling design and the tip geometry shaping tends to be too computationally expensive. This study adopts the multiscale method in a commercial solver to provide a fast and accurate solution for the turbine tip cooling design. The method uses source terms added on the coarse mesh to generate the solution that is close to the one obtained with a well-resolved mesh. The source terms are found to present not only the influence of the mesh resolution but also the flow injection. The multiscale results have been validated against the experimental data and the fine mesh results. The agreement shows the potential for this method to be used in cases with large length scale disparity.

Impact failure in two silicates revealed by ultrafast, in situ, synchrotron X-ray microscopy

To travel safely behind screens that can protect us from stones and hail, we must understand the response of glass to impact. However, without a means to observe the mechanisms that fail different silicate architectures, engineering has relied on external sensors, post-impact examination and best-guess to glaze our vehicles. We have used single and multi-bunch, X-ray imaging to differentiate distinct phases of failure in two silicates. We identified distinct micromechanisms, operating in tandem and leading to failure in borosilicate glass and Z-cut quartz. A surface zone in the amorphous glass densifies before bulk fracture occurs and then fails the block, whilst in quartz, fast cracks, driven down cleavage planes, fails the bulk. Varying the rate at which ejecta escapes by using different indenter tip geometries controls the failed target’s bulk strength. This opens the way to more physically based constitutive descriptions for the glasses allowing design of safer, composite panels by controlling the impulses felt by protective screens.

Measurement of Pressures Generated in Root Canal During Er:YAG Laser-Activated Irrigation.

Objective: To measure distribution of pressures along the depth of the root canal during erbium-doped yttrium aluminum garnet (Er:YAG) laser-activated irrigation (LAI) with different modalities and fiber tip (FT) geometries. Background: A new LAI modality based on the delivery of synchronized pairs of Er:YAG laser pulses to generate enhanced irrigant streaming and shock wave emission was recently introduced. However, the influence of FT geometry on efficacy and comparison with single pulse modality is not yet presented. Methods: Pressures within a simulated root canal were simultaneously measured at 5 depths during LAI. Seven FT geometries (conical and cylindrical) and two modalities [Super Short Pulse (SSP) and dual pulse AutoSWEEPS] were compared. Results: Under the same conditions, average pressures using SSP at 20 mJ of laser energy ranged from 111 Pa for a conical 600 μm FT to 225 Pa for a flat 400 μm FT. The measured pressures for the SSP and the AutoSWEEPS at 20 mJ laser energy were 223 and 308 Pa at the most coronal level and 119 and 126 Pa at the apical constriction, respectively. Measured pressures and irrigant penetration depths at different root canal levels were found to be linearly correlated (R2 = 0.82; p < 0.01). Conclusions: The generated pressures get progressively reduced from the coronal toward the apical third of the root canal. A strong dependence on the FT design and laser modality was observed. Within the limitations of the study, the AutoSWEEPS modality is more effective than standard SSP in generating pressures within the root canal, without increasing the risk of extrusion.

Microbial Cross-contamination in Multidose Eyedrops: The Impact of Instillation Angle and Bottle Geometry.

PurposeTo evaluate the impact of instillation angle and nozzle tip geometry on cross-contamination risk of multidose ocular solution bottles.Methods Pseudomonas aeruginosa solution was passed exclusively on the outside of the nozzle to simulate contamination on the exterior of topical agents. Three drops were administered from angles of 90° and 45° from bottles with either a round or sharp tip geometry, and the cultures were examined for growth. Two-hundred sixteen cultures from nine lubricant eyedrop brands currently existing in the Brazilian market were assessed for bacterial growth.ResultsAfter seven days, bacterial contamination was detected in 53.7% of cultures when drops were administered at 90° and in 70.4% of cultures at 45°. Eyedrops collected from a rounded nozzle tip and an instillation angle of 90° transmitted bacteria in 69.4% of cases, whereas those administered from a sharp tip transmitted bacteria in only 22.2% of cases (P = 0.001). At an instillation angle of 45°, contamination was identified in 83.3% of bottles with a rounded tip geometry and in only eight of 18 bottles (44.4%) from those with a sharp nozzle geometry (P = 0.005).ConclusionsAdjusting the instillation angle of eyedrop solutions to 90°, as well as using a nozzle geometry that prevents flow of the solution to the side of the bottle, significantly reduced contamination rates.Translational RelevanceStandardizing drop bottles and adjusting delivery angle shows promise in reducing contamination rates and may critically impact the quality of care for patients requiring topical therapeutic agents.