Low Contact Pressure Research Articles

Comparative study of a femoral amputated limb with and without implant

The contact pressure at the socket–residual limb interface is the most critical parameter for evaluating the comfort of a leg prosthesis. Experimental studies have analyzed this parameter for typical postures and during walking on a flat surface of an amputee; however, experimental tests require a real socket prototype equipped with transducers. To optimize socket design, this work presents a virtual approach based on a digital avatar of a patient wearing a lower limb prosthesis. Our study integrates two different types of simulations: the first concerns the femur with an implant, the second without an implant, and includes the evaluation of pressure at the socket–residual limb interface using finite element analyses (FEA). The objective of this study is to understand the distribution of loads and stresses at the interface between the residual limb and the prosthesis. The lower contact pressure is represented by CPRESS, while CSHEAR1 is the frictional shear stress component in the first local tangent direction, and CSHEAR2 is the frictional shear stress component in the second local tangent direction.

Test and sensitivity analysis of base‐isolated steel frame with low‐friction spherical sliding bearings

AbstractIn Japan, spherical sliding bearings with low friction coefficients are gaining popularity for base‐isolating low‐rise frames that are relatively lightweight. However, the complete dataset of isolators and a base‐isolated frame for evaluating the model sensitivity and response uncertainty are limited. This study first presents the design process, isolation unit‐ and frame‐level testing, and a blind prediction contest conducted on the occasion of full‐scale shaking table testing of a three‐story base‐isolated hospital specimen. The design process utilizes a numerical model that accounts for the velocity and contact pressure dependencies and requires soft‐ and hard‐case simulations with nominal friction coefficients plus and minus standard deviation to consider the uncertainties associated with the bearing behavior. The pre‐shipment isolation unit and frame shake table testing yielded an invaluable dataset for bearings under normal and low contact pressures, low and high velocities, and constant and varying axial loads. The accompanying blind prediction contest provided a valuable dataset for rethinking the impact of modeling uncertainty. In‐depth data analysis and sensitivity analysis were conducted. The sliding coefficient increased under low‐contact pressure and low‐velocity conditions. The static friction coefficient was 1.9 to 4.5 times higher than the dynamic coefficient, but this had little impact on the residual displacement, cumulative travel, and maximum story shear force. The axial force fluctuation, vertical motion, and two‐directional input did not significantly affect the bearing behavior in the test. The test and the following simulations confirmed that the low friction coefficient helped the building contents, that is, medical equipment in this study, remain in order under near‐fault and long‐period ground motions.

On the time-dependent sliding contact behavior of three-phase polymer matrix smart composites

Abstract Three-phase smart composites consisting of magnetostrictive and piezoelectric reinforcements embedded with a polymer matrix can achieve specific multifunctional properties in response to external stimuli, which are well-suited for the application of sensors, actuators, and electronic devices. The materials exhibit complex behaviors characterized by electro-magneto-viscoelasticity coupling during the contact of these smart structures. This paper proposes a novel hybrid element method (HEM) for numerically analyzing the frictionless sliding contact problem stemming from the viscoelastic behavior and multiphase interactions of polymer matrix smart composites. The study aims to fully investigate the effects of material properties, sliding velocities, and action time on the contact behavior of materials via the integration of the conjugate gradient method (CGM) with the discrete convolution-fast Fourier transform (DC-FFT) algorithm. The analytical viscoelastic frequency response functions (FRFs) are derived by substituting elastic solutions with the time-dependent relaxation modulus. Numerical results show that three-phase polymer matrix smart composites exhibit lower contact pressure and higher surface electric/magnetic potential than three-phase magneto-electro-elastic composites. Sliding velocity and action time strongly influence the distribution of pressure/stress and electric/magnetic potential.

UNVEILING THE INFLUENCE OF ONE-LEG STANCE AND STANDING UP FROM A CHAIR ON HUMAN HIP JOINT PROSTHESIS USING FINITE ELEMENT CONCEPTS

The hip joint plays an important role in providing stability to the human body. Factors such as aging, wear, and tear, make the hip joint degenerate and, in such cases, the same to be replaced through hip arthroplasty surgeries. The background of this study aims to investigate the contact consequence between the artificial femoral head and the acetabular cup for different bearing couples during one-leg stance and standing up from a chair, utilizing the finite element method. The three-dimensional finite dynamic contact model has been developed with different material combinations. The results obtained by the present finite element model align well with the previously available literature. The parameters investigated include maximum von Mises stress, maximum contact pressure and deformation for different material combinations. The results reveal that the pair i.e., Alumina on Ultra-high molecular weight polyethylene (UHMWPE) exhibits lower contact pressure, von Mises Stress and deformation. Therefore, the material pair i.e., Alumina on UHMWPE can be employed in the Total hip replacement (THR) to mitigate contact consequences under both static and dynamic loading conditions, thereby enhancing the durability of the artificial joints.

Degradation Processes of Two Compound Layers on Nitrided Surfaces During the Wear Test by “Block on Hot Al Cylinder”

The results obtained in the study help to explain the degradation process of the nitrided steel compound layer. Compound layers with different properties on gas-nitrided H10 tool steel blocks were tested for wear with “block on hot Al cylinder”. Degradation processes were observed on both compound layers with different properties and at three contact pressures. In order to observe the degradation processes in the compound layers, the wear tests were interrupted at various fixed time intervals and the resulting changes were closely monitored. The comprehensive analysis highlighted the complexity of the degradation process in the compound layers and emphasized the existence of complex relationships between the above-mentioned parameters. The reaction of the nitrided steel surface with hot Al is more pronounced in areas with lower contact pressure, while adhesive removal and furrow formation are pronounced in areas with low and medium contact pressure. This process begins with a sufficient density of the areas where islands of adhesive removal are located, their enlargement during the test, the breaking up of the walls between them, and finally the removal of the compound layer in the sliding direction, which appears as furrowing in the final phase of wear.

Dry sliding wear and friction performance of zirconium dioxide tribopairs

Zirconium is an attractive engineering material owing to its commendable temperature, corrosion resistance, and excellent biocompatibility. Despite these merits, its industrial applicability is hindered by elevated wear and friction in tribological settings. Previous research has concentrated on unmatched pair contacts involving zirconium and alumina primarily due to the exceptional hardness. However, there is a noticeable dearth of literature on the matched pair contact condition for zirconium dioxide. Thermal oxidation is a promising and cost-effective method to address the suboptimal tribological performance and enhance the mechanical and electrochemical properties of zirconium. In this study, thermal oxidation is employed to produce a 6-μm-thick oxide layer in an air furnace at 650°C for 6 h. Subsequently, the resulting surface coating was tribologically tested using a pin-on-disc tribometer against two distinct counterface materials, namely, alumina and zirconium dioxide, in a dry and unlubricated environment. The findings reveal that matched contact between the zirconium dioxide tribopair is unfavorable, leading to elevated friction and wear rates. Consequently, this configuration should be avoided in dry contact situations characterized by high contact pressures. However, under lower contact pressures, the wear performance is acceptable. Furthermore, when combined with lubrication, this system may have potential applications in bio-tribological systems.

The friction of surface textured cylinder liner segments modified by Direct Laser Writing and Direct Laser Interference Patterning processes

Direct Laser Writing (DLW) using ultrashort pulsed lasers and galvanometer scanning, has become an established process for surface texturing, allowing an extensive variety of feature geometries and texture designs to be produced. The minimum feature sizes that can be generated are however limited by factors such as the laser output power, beam diameter, beam wavelength and associated optics. To address the need to produce even smaller texture features, Direct Laser Interference Patterning (DLIP) has been developed, which utilises bespoke beam splitting and converging optics to produce periodic interference fringing and enabling surface textures in the micrometric size range to be produced.In this study, the texturing of cast iron cylinder liner segments using DLW and DLIP processes is explored, to assess their tribological performance in high efficiency internal combustion engines, such as for hybrid applications. To facilitate the designs of textures and to capture high resolution data on surface interactions at specific points in the combustion cycle, the segmentation of cylinder lines and piston rings is undertaken. The results of tribology tests covering combinations of high and low speeds and contact pressures, have shown that the mechanical honing of cylinder liners could potentially be replaced with the cleaner DLIP texturing as an alternative.Optimised texture designs using the DLW process achieved up to a 54 % reduction in kinematic friction between the piston ring and textured cylinder liner surfaces, compared with mechanically honed cylinder liner segments. These results have indicated that DLW texturing offers the best improvement in friction performance in the boundary and mixed lubrication regimes at higher contact pressures, at both lower and higher sliding speeds. The results also provide useful comparative data on the performance of meso and micrometric scale textures and how they can be best applied to cylinder liners.

On the Use of Foam Rubber for Sealing Applications

O-rings made from foam rubber are often used in sealing applications. Foam rubber have low (macroscopic) elastic modulus E0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$E_0$$\\end{document} resulting in a low nominal contact pressure when squeezed against a countersurface. In most cases the foam rubber is covered by a thin surface film with the effective elastic modulus E1>E0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$E_1 > E_0$$\\end{document}. We show that the nominal contact pressure may not be high enough for the contact area to percolate and the O-ring seal will leak. For the leakage calculations we use the Persson multiscale contact mechanics theory, and the (modified) Bruggeman effective medium theory for the fluid flow conductivity. The experimental input for the theory are surface roughness power spectrum, which was obtained from stylus topography measurements, and the elastic properties (E0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$E_0$$\\end{document} and E1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$E_1$$\\end{document}) of the rubber O-ring. As an application of this calculation method, we have used the preliminary as well as the final results of the laboratory gas tightness tests of the 136 New Small Wheel Micromegas Quadruplets performed at CERN, from February 2019 to May 2021, in the framework of the ATLAS Experiment upgrade. In the integration quality control, a novel method for gas tightness measurement, that we have called “Flow Rate Loss”, has been used as a baseline method.Graphical

Design, construction and test of a prototype coil with demountable CuBe joints for pulsed table-top tokamaks

In a classic small tokamak, the magnetic confinement is achieved by toroidal coils that fit into a donut-shape mechanical structure. To facilitate their handling and maintenance as well as the access to various auxiliaries components, their design has evolved toward a modular configuration. For such demountable design, it is important to guarantee the electrical continuity of the winding of the coil across the modular parts through electrical contacts. The resulting joints rely on pressure and specific materials to transfer high current densities at a good mechanical stability and manageable losses. In the present work, a prototype of a circular demountable toroidal field coil (CDTFC) was designed and built to test some technical choices to be used in the final coils of a table-top tokamak referred to as TPM-1U. For this small tokamak, the magnet wires to wind the toroidal coils should be able to handle large pulsed currents in the tens of thousands of Amperes whereas the coil joints should handle a peak current density of at least 75 kA/cm2. The case study here is the TPM-U1 table-top tokamak. Its conceptual design is recalled and mechanical and magnetic details of the demountable coil prototype are provided. For the experimental test, the contacts were slightly pressed using a custom-made contact assembly and current pulses between 4 kA and 8 kA were fedto the coil prototype. The degradation of the joint was visually estimated by assessing the amount of micro-melting, plastic deformation and oxidation appearing at the interface between the materials in contact. It is shown that the selected AWG-04 magnet wire is appropriate for carrying kiloAmpere range pulsed currents and that the CuBe contacts are able to withstand current densities larger than the specification, up to 263 kA/cm2, under low contact pressures of a few mega-Pascal simplifying their handling. Some technical choices have been probed on a prototype coil yielding a generic sequence of tasks to build and test mechanically and electromagnetically demountable coils and their joints.

Competition-Induced Macroscopic Superlubricity of Ionic Liquid Analogues by Hydroxyl Ligands Revealed by in Situ Raman.

High load-bearing capacity is one of the crucial indicators for liquid superlubricants to move toward practicality. However, some of the current emerging systems not only have low contact pressures but also are highly susceptible to further degradation due to water adsorption and even superlubricity failure. Herein, a novel choline chloride-based ionic liquid analogues (ILAs) of a superlubricant with triethanolamine (TEOA) as the H-bond donor is reported for the first time; it obtains an ultralow coefficient of friction (0.005) and high load-bearing capacity (360 MPa, more than 2 times that of similar systems) due to adsorption of a small amount of water (<5 wt %) from the air. In situ Raman combined with 1H NMR and FTIR techniques reveals that adsorbed water competes with the hydroxyl group of TEOA for coordination with Cl-, leading to the conversion of some strong H-bonds to weak H-bonds in ILAs; the localized strong H-bonds and weak H-bonds endow the ILAs with high load-bearing capacity and the formation of ultralow shear-resistance sliding interfaces, respectively, under the shear motion. This study proposes a strategy to modulate the interactions between liquid species using adsorbed water from air as a competing ligand, which provides new insights into the design of ILA-based macroscopic liquid superlubricants with a high load-bearing capacity.

Equivalent thin-layer temperature field model (ETTM) for bolted rotors to describe interface temperature jump

Improving the accuracy and efficiency of predicting the temperature field is a crucial requirement for iteratively calculating and online monitoring the temperature field, particularly for combined structures. The heat flow movement is impeded by incomplete interface contact, resulting in a temperature jump. To address this, the equivalent thin-layer temperature field model (ETTM) is proposed to replace the interface thermal contact conductance (TCC) model. Firstly, the fractal TCC model of a bolt connection is derived based on fractal geometry. Subsequently, the contact surface of the circumferential bolt connection is considered to be the parallel connection of multiple bolt thermal resistances. The TCC of the equivalent thin-layer is obtained. Building on this, the ETTM of the built-up rotor structure is developed. Finally, a temperature field model of the bolted rotor is derived. The validity of models is verified by comparing the model proposed in this paper with the previous research findings and ANSYS analysis results. Numerical simulation results reveal that TCC is influenced by several factors: contact pressure, the nominal contact area within the fractal domain, fractal dimension, fractal roughness, and the root mean square (RMS) height. Furthermore, the effects of the thickness of the thin layer model and the thermal conductivity of the material on heat transfer are examined. Ultimately, the findings indicate that heat transfer at the interface is significantly impeded by thermal contact resistance across various temperature boundary conditions. Notably, lower contact pressure intensifies this impedance.

In-situ micro-asperity investigation of real contact area formation during sliding with the effects of roughness and normal load considered

Real contact area is a challenging phenomenon in tribology, where despite established theoretical models, detailed experimental studies are still lacking. This work is focused on the evolution of the real contact area of multi-asperity steel contacts during sliding, by using sub-micron characterisation of entire multi-asperity contact area and simultaneous measurement of the friction force. Steel-sapphire contact was monitored by using an in-situ optical system in real time during 5 mm of unidirectional sliding in surface roughness range Ra = 0.1–1.0 µm and normal loads up to the nominal contact pressure equal to steel yield strength (Y). The results showed that the initial real contact area caused by static loading increased during sliding. At low nominal contact pressure of 0.3Y, the increase in real contact area was the largest: for Ra = 0.1 µm it went from 9.5% of the nominal area under static conditions to 15.0% after sliding, a 56% relative increase, and for Ra = 1.0 µm it went from 5.0% to 11.5% after sliding, a 106% increase. The increase in real contact area was smaller at higher nominal contact pressures of 0.6Y and 1.0Y. At 1.0Y for Ra = 0.1 µm the real contact area went from 18.0% to 21.8% after sliding and for Ra = 1.0 µm it went from 9.4% to 12.9% after sliding. The coefficient of friction increased with roughness at the lowest nominal contact pressure 0.3Y (for Ra = 0.1 µm it was 0.24 and for Ra = 1.0 µm it was 0.29) but became independent of roughness at higher contact pressures (on average 0.18).

Performance Evaluation of a Height Adjustable Mini Combine Harvester

Mini combine harvesters have been very popular among paddy farmers. The compact size of the machine, in addition to the axial flow threshing mechanism and the effect of low ground pressure on paddy soil, makes it a potential alternative for efficient paddy harvesting of a height-adjustable mini combine harvester used for harvesting paddy fields. This type of harvester was tested in typical paddy field conditions planted with MR297 variety at MARDI Seberang Perai. The performance tests included measuring theoretical and effective field capacity, field efficiency, soil bearing capacity before and after machine disturbance and machine slippage. The fuel consumption was also recorded. The combined harvesting losses were also measured during the experiment. Results showed that in wet and muddy conditions, the mini combine harvester obtained a theoretical field capacity (TFC) of 1.28 ha/hr, effective field capacity (EFC) of 0.94 ha/hr and a field efficiency (FE) of 73.4%. The average fuel consumption of the mini combine harvester was 25 L /ha. The wheel slippage in wet paddy fields was 2.18% and on farm roads was 1.55%. The mini combine harvester also contributed to producing less ground effects, combined with the use of low ground contact pressure tracks, that caused minimal soil disturbance that would affect the soil hardpan layer. This mini combine harvester produced an average harvesting loss of 2.3% with an average harvesting impurity of 10.65%. The mini combine harvester had enough power to move in typical paddy field conditions, with no soft soil problems. The mini combine harvester was able to turn 360 degrees within a small area, which made it suitable for harvesting in paddy fields. Thus, this mini combine harvester has the potential to be used for paddy harvesting with the ability to not only produce minimal harvesting loss, but also produce less ground contact pressure which can help to manage the soil hardpan layer from being easily damaged.

In Vitro Wear Behavior of Knee Implants at Different Load Levels: The Impact of the Test Fluid

Calf serum is defined as a test fluid for in vitro knee wear simulation studies in the ISO standard. However, protein degradation typically occurs during in vitro wear simulation. The current study should indicate whether increased loads change the rheological properties of the test fluid and may, therefore, lead to favorable tribological behavior and reduced wear. Three different load levels were simulated in a displacement-controlled knee wear simulation study. The gravimetric wear rates were determined, pressure measurements were performed, and the dynamic viscosity of the test fluids were analyzed after the simulation of 0.5 × 106 cycles. The lowest load level led to the lowest wear rate, and the lowest contact pressure and contact area, compared to the medium and high-load level. Although, the high-load level led to the highest contact pressure and contact area, the wear rates were comparable to the medium-load level. The rheological measurements revealed the highest dynamic viscosity for the high-load level and no differences could be found between the medium and low loading condition. To perform realistic wear simulation studies, the reproduction of the in vivo interrelationships between the shear forces and wear are necessary.

도로와 험지 주행이 가능한 구동부 설계

The applications of robots are increasing progressively along with their capabilities. A driving unit is an essential element in any robot and the performance of the robot is directly related to its performance. This study aims to design a transmission that adopts multiple caterpillar and wheel driving arrangement with low contact pressure for versatile applications. The limitations of similar previous studies are highlighted and a practical model to address them is presented. FEM analysis and formulae are applied for system optimization. Driving and switching can be done using a pair of motors and actuators connected to the rear wheel. The wheel axis is mechanically connected to the motor and the tension is adjusted by pose change through the actuator of the outer pulley on the parallel axis. This helps to overcome the problem and allows continuous operation by eliminating the delay time when switching a driving pose. The stability of the system is verified through stress analysis of the deceleration system, where the largest torque is applied internally. Finally, the validity of the proposed design is proved through the fabrication of a mock-up model of actual size.

Atomic-Scale Understanding on the Tribological Behavior of Amorphous Carbon Films under Different Contact Pressures and Surface Textured Shapes.

The textured design of amorphous carbon (a-C) film can significantly improve the tribological performance and service life of moving mechanical components. However, its friction dependence on different texture shapes, especially under different load conditions, remains unclear. In particular, due to the lack of information regarding the friction interface, the underlying friction mechanism has still not been unveiled. Therefore, the effects of contact pressure and textured shapes on the tribological behavior of a-C films under dry friction conditions were comparatively studied in this work by reactive molecular dynamics simulation. The results show that under low contact pressure, the tribological property of a-C film is sensitive to the textured shape, and the system with a circular textured surface exhibits a lower friction coefficient than that with a rectangular textured surface, which is attributed to the small fraction of unsaturated bonds. However, the increase of contact pressure results in the serious reconstruction and passivation of the friction interface. On the one hand, this induces a growth rate of friction force that is much smaller than that of the normal load, which is followed by a significant decrease in the friction coefficient with contact pressure. On the other hand, the destruction or even disappearance of the textured structure occurs, weakening the difference in the friction coefficient caused by different textured shapes of the a-C surface. These results reveal the friction mechanism of textured a-C film and provide a new way to functionalize the a-C as a protective film for applications in hard disks, MEMS, and NEMS.

Effect of Lubricant Properties and Contact Conditions on False Brinelling Damage

False brinelling is a type of fretting wear that occurs in rolling bearings when the contacts of bearing rings and rolling elements are subjected to small-amplitude oscillatory motion. It manifests itself as deep craters with relatively polished bottoms that are evenly spaced around the bearing rings. This work investigates the influence of lubricant properties and contact conditions, including oil viscosity, applied load, and amplitude and frequency of oscillations, on the onset and progression of false brinelling damage. Experiments were conducted with AISI 52100 bearing steel specimens in a ball-on-flat configuration under small-amplitude oscillating conditions. A set of base oils and a group of custom-made greases with systematically varying properties were employed. Importantly, the same ball-on-flat setup was adapted to allow optical access to the contact by employing a sapphire disc instead of a steel one. This allowed direct observation of the damage onset and progression to better elucidate the mechanisms taking place. Additional experiments were conducted with the same lubricants on a thrust ball bearing rig and the observed trends were compared to those from the ball-on-disc setup. Results show that false brinelling damage initiates locally at discrete asperity microcontacts and then spreads relatively quickly with continued rubbing to cover the whole contact area. Oscillation amplitudes shorter than the Hertz contact width (A/D < 1) were shown to be most damaging, while the damage reduces drastically for amplitudes larger than the Hertz contact width (A/D > 1). For the more important case of A/D < 1, oils and greases with lower viscosities produced less damage. Oils in general produced somewhat less damage than the equivalent lithium- or urea-thickened greases with the same base oil. Lower oscillation frequencies and lower contact pressures also produced less damage. The corresponding friction and electrical contact resistance measurements indicate that under these conditions of A/D < 1 the contact operates under boundary lubrication at best but can intermittently approach effectively dry conditions, depending on lubricant properties and applied conditions. These observations indicate that the key variable that controls damage when the oscillation amplitude is less than the contact width is the ability of the lubricant to penetrate and remain in the oscillating contact. Therefore, lubricant properties and contact conditions that promote this penetration, which may be different from those that promote hydrodynamic film formation, can mitigate against false brinelling.

Quantifying the inlet pressure and shear stress of elastohydrodynamic lubrication

Central film thickness in elastohydrodynamic lubrication is governed by lubricant properties in the low-pressure contact inlet. A relevant definition of pressure-viscosity coefficient would require knowledge of the maximum inlet pressure. The maximum inlet shear stress determines if the Newtonian assumption is valid. Using numerical simulations, the maximum inlet pressure is found, wherein changes in viscosity continue to influence film thickness. It is found to depend on operating conditions, and it ranges from 50 to 185 MPa. The maximum inlet shear stress is found to reach up to 2 MPa. Analytical formulas are offered for predicting maximum inlet pressure and shear stress. These allow for a refined definition of the pressure-viscosity coefficient, restricted to a clearly-defined contact inlet.

Biomechanical characteristics of self-expanding sinus stents during crimping and deployment_A comparison between different biomaterials

Self-expanding sinus stents are often used in functional endoscopic sinus surgery to treat inflamed sinuses. The PROPEL self-expanding sinus stent offers mechanical support to the sinus cavity to prevent restenosis. The stent is made of a bioabsorbable material (PLGA) that disappears after wound healing. However, complications such as foreign body sensation and severe stent migration/expulsion have been reported after implantation. Little is known about the contact characteristics of self-expanding sinus stents from when the stent is crimped into the insertion device through to deployment into the sinus cavity. This current study developed a test platform to analyze the biomechanical behavior of the stent during this process. Three common bioabsorbable materials, PLGA, PCL and Mg alloy, were evaluated to understand how the choice of material affects the biomechanical characteristics of self-expanding sinus stents. The results showed that the material can have a considerable influence on the contact characteristics during crimping and deployment. When crimped, the PLGA and Mg alloy stents showed much higher plastic strain and contact stress than the PCL stent. When deployed, the PCL stent had the largest contact area (4.3 mm2) and the lowest contact pressure (0.1 MPa) on the inner surface of the sinus canal. The results indicate that PCL could be a suitable choice for self-expanding sinus stents. This current study provides a method for observing the biomechanical characteristics of sinus stents during stent crimping and deployment.

Law of diffusion bubbles produced by high-voltage pulsed electric field in liquid

Pulsed electric field is a novel physical energy source for treating atrial fibrillation and tumor ablation, which has advantages over traditional thermal ablation, such as being non-thermal, short treatment time, tissue selectivity, and low contact pressure requirements. The diffusion bubbles generated during physical ablation may lead to gas embolism and silent cerebral events, with potential hazards such as tissue damage and cerebral ischemia. Previous studies have shown that the number of bubbles generated is correlated with the electrical properties of the treated object, pulse parameters (pulse waveform, treatment time and input energy), and electrodes. The number of bubbles are more significant at the cathode than at the anode, and the number of bubbles positively correlates with the input energy. However, to the best of our knowledge, no studies have been conducted to investigate the effects of ablation pulse parameters on diffusion bubbles. Therefore, in our experiment, a platform for producing pulses and observing diffusion bubble is built, and the needle-ring electrode we made realizes the capture and measurement of diffusion bubbles. Since pulses with a voltage of 3 kV and a pulse width of 100 μs are commonly used as ablation parameters for atrial fibrillation and tumor in pulsed field ablation (PFA), the pulse width of unipolar pulse is selected as 5, 10, 50, and 100 μs, and the number of pulses applied is 1. The pulse voltage is determined according to the parameters commonly used in PFA and the simulation calculation of the field strength distribution of the needle-ring electrode. After determining the parameters, this experiment explicitly investigates the relationships among diffusion bubbles and solution conductivity, pulse voltage, pulse width, input energy, and other parameters. Meanwhile, the size distributions of diffusion bubbles under different operating conditions are statistically investigated. Besides, the possible causes of diffuse bubbles are also explored. We evaluate the number of bubbles by measuring the cross-sectional area of the diffusion bubbles from a top-down perspective. The experimental results show that the area of diffusion bubbles generated in the liquid is positively correlated with pulse voltage and input energy; high conductivity and long pulse width can enhance the thermal effect and increase the area of diffusion bubbles; diffusion bubbles with a diameter larger than 100 μm are easily generated under high conductivity and high pulse width conditions. By speculating on the results, the electrolytic reaction may be the main source of diffusion bubbles when the needle electrode is the cathode. This study is expected to optimize future pulsed electric field ablation parameters.