Asymmetric Tip Research Articles

Free Crushed Cartilage Filler Graft to Optimize Tip Aesthetics in Asian Rhinoplasty.

The thick skin and weak cartilages make tip rhinoplasty very challenging in Asian patients. Most require an open approach for structural grafting in order to achieve the desired projection and rotation. This need for substantial tip grafting may result in subtle imperfections that are only noticed as the incisions are closed. This study describes the senior author's technique of free crushed cartilage filler graft to optimize nasal tip aesthetics in Asian rhinoplasty. The goal is to introduce this easy-to-use and effective technique to refine the final nasal tip aesthetic with immediate visual and tactile feedback. This is a retrospective review of all patients with free crushed cartilage filler graft with at least 12months of follow-up. Medical records were reviewed for patient demographics, intra-operative manoeuvres, and complications. Photographs were analysed to evaluate changes in nasal length, tip height, and nasolabial and columellar-labial angles as well as aesthetic complications. Sixty-six patients were included in this study, with an average follow-up of 16.3months. Nasal length was 8.3% greater than pre-op (P < 0.01), and nasal tip height was 12.7% greater than pre-op (P < 0.01). Aesthetic analysis demonstrated that 6.1% of patients had an amorphous tip, 3.0% had an irregular or asymmetric tip, and 4.5% had visible tip grafts. 12.1% of patients expressed aesthetic dissatisfaction, but none was recommended for or pursued revision surgery. When used correctly, free crushed cartilage filler graft can improve the final tip aesthetic and help camouflage underlying prominences to give the patient a natural result. This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Determining the angle of the frontal working surface of the soil-piercing head asymmetrical tip for static soil-piercing

Problem. From the analysis of the technical literature, it was established that among the trenchless technologies for laying underground engineering communications and service pipelines, the technology with the possibility of forming a horizontally directed communication cavity in the soil using soil-piercing installations of static action is the most common. Goal. This method consists in forcefully pressing a soil-piercing working body, which has the form of a conical-cylindrical projectile, into the soil. At the same time, the well is formed by radial extrusion of the soil around the formed well. However, the use of such equipment does not provide high accuracy, which limits its practical application within 20 m. It is not sufficient for modern requirements of creating transitions during the laying of communications. Methodology. One of the ways to improve the efficiency of laying underground networks is to extend this method over a longer distance by correcting the trajectory of the working body. This is achieved by using a soil-piercing head with an asymmetric tip. Due to this, in addition to the axial resistance of the soil, a transverse component force appears, which deflects the head during its advancement in the soil. The question of determining the angle of displacement of such a tip is important in terms of the process control. Results. In the paper, a calculated dependence is proposed for determining the rational value of the angle of inclination of an asymmetric tip working surface, which is a flat plane cut at the angle of a cylinder. An analysis of the dependence of the angle of the working surface inclination on the physical and mechanical properties of the soil is also given. Originality. It was determined that the maximum angle of inclination of the frontal surface is determined by the conditions of soil descent from it. Its maximum value, for example when working in loam, should not exceed 55o-67o for a tip made of steel. Practical value. The obtained calculated dependence can be useful for determining the angle of inclination of the flat frontal surface of the tip of the soil piercing working tool for controlled static soil piercing at the stage of designing networks and choosing an effective method for drilling a well under roads or other obstacles.

Nonlinear Energy Harvesting From a Base Excited Size-Dependent Flexoelectric Nanostructure with Off-Center Rigid Tip Mass Subjected to Axial Pulsating Excitation

This study explores the incorporation of flexoelectricity and size-dependence effects in electricity harvesting from a novel nanostructure. This nanostructure, featuring a cylindrical-shaped rigid tip mass, is stimulated at the base with axial pulsating excitation. Designed with a nanobeam material, the energy harvester accounts for structural nonlinearity, flexoelectricity, and the presence of an off-center rigid mass, operating under multiple excitations. The eigenanalysis is employed to delve into the dynamic characteristics of the system, providing engineers with insights to identify safe operating regions and operational constraints. Additionally, perturbation techniques are utilized to estimate steady-state voltage and power characteristics, with a focus on maximizing voltage and power generation. The study underscores the impact of size dependence on nanoscale design, flexoelectricity, asymmetric tip mass, and various excitation parameters within a constrained operating range. Analysis reveals how saddle-node and pitchfork bifurcations can disrupt energy harvesting performance and suggests strategies for mitigating these issues by adjusting operational parameters. Moreover, the study emphasizes the significant role of the off-center rigid tip mass in energy estimation compared to conventional microstructure-based energy harvesters. Analytical findings are rigorously validated against numerical results under different resonant scenarios, showcasing the accuracy of the analytical approach in capturing nonlinear sources and optimizing energy harvesting from nanostructures.

Biointerfaces with ultrathin patterns for directional control of cell migration

In the context of wound healing and tissue regeneration, precise control of cell migration direction is deemed crucial. To address this challenge, polydimethylsiloxane (PDMS) platforms with patterned 10 nm thick TiOx in arrowhead shape were designed and fabricated. Remarkably, without tall sidewall constraints, MC3T3-E1 cells seeded on these platforms were constrained to migrate along the tips of the arrowheads, as the cells were guided by the asymmetrical arrowhead tips which provided large contact areas. To the best of our knowledge, this is the first study demonstrating the use of thin TiOx arrowhead pattern in combination with a cell-repellent PDMS surface to provide guided cell migration unidirectionally without tall sidewall constraints. Additionally, high-resolution fluorescence imaging revealed that the asymmetrical distribution of focal adhesions, triggered by the patterned TiOx arrowheads with arm lengths of 10, 20, and 35 μm, promoted cell adhesion and protrusion along the arrowhead tip direction, resulting in unidirectional cell migration. These findings have important implications for the design of biointerfaces with ultrathin patterns to precisely control cell migration. Furthermore, microelectrodes were integrated with the patterned TiOx arrowheads to enable dynamic monitoring of cell migration using impedance measurement. This microfluidic device integrated with thin layer of guiding pattern and microelectrodes allows simultaneous control of directional cell migration and characterization of the cell movement of individual MC3T3-E1 cells, offering great potential for the development of biosensors for single-cell monitoring.

Proliferation in the photo-response characteristics of MDC thin films for optoelectronic applications through NSP technique

Nebulizer spray pyrolysis (NSP), a simple thin-film deposition method, was used to fabricate p-Si/n-manganese-doped cerium oxide (MDC)/Al photodiodes. The structure, morphology, optics, composition, electrical and rectifying properties of the prepared materials were analyzed. UV-Vis analysis demonstrates a prominent and acute absorption edge at 425 nm in the visible region. As more Mn impurities are incorporated into CeO2 crystallites, the band gap decreases as the doping level increases, leading to the formation of new recombination sites with low energy emissions. Electrons in outer orbits operate in energy bands, moving to higher energy levels. At higher Mn doping, some NBE emissions and green emission peaks disappear. The emission spectrum confirmed that strong and broad blue emission peak occurred for the diode containing the 15% Manganese Diode Cerium film. XRD peak shows the mono-phase polycrystalline cubic fluorite structure with the main orientation in the 200 directions. The broad lines (CeO) symmetry at 695,659,538 and 517 cm−1 observed in the Fourier Transform -Infrared spectrum are due to the phonons of the cerium oxide (Ce-O) network caused by asymmetric tip stretching and fastening vibration. Satellite peaks arise due to the transition from ligand (O 2p) to metal (Ce 4f) achieved during the primary and main photo-ionization process. This suggests that the valence states of Ce3+ and Ce4+ provide access to the CeO2 lattice sites. The I-V properties of p-Si/n-MDC/Al devices show behavior limited by the properties of the inorganic semiconductor substrate and the size of the hetero-interface energy barrier. The switching voltage of the hetero-junction was found to be approximately 2.4 V.

Effect of asymmetrical tip clearances on energy performance and cavitation characteristics of NACA0009 hydrofoil in tidal energy

Effect of asymmetrical tip clearances on energy performance and cavitation characteristics of NACA0009 hydrofoil in tidal energy

Automatic control of soil puncture

Among the existing methods of making horizontally directed wells for trenchless laying of utilities, the method of static soil puncture is the most popular. The main disadvantage of this method is poor accuracy of the piercing head movement in the soil. This drawback requires constant adjustment of the trajectory of this movement. The movement of the head is controlled by using a head with an asymmetric tip and the action of translational and translational-rotational motion on it. The transmission of these movements from the power plant is accomplished by means of a set of fixed pushing rods. If you know how the process of off and on deviation of the head happens, you can make it possible to automatically control the puncture of the soil by timely changing the direction of the head tip shift.&#x0D; To achieve this goal, the following issues have been resolved. It is determined that for automated control of the soil puncture process by static method it is necessary to use a puncture head with an asymmetric tip. Changing its position in the soil space can be controlled by rotating the tip and orienting it according to the direction of deviation.&#x0D; The obtained mathematical model of correcting the trajectory of the head with a truncated cylindrical tip makes it possible to predict the process of soil puncture in time depending on different soil conditions and to get a solution to the problem of deviation from the specified design trajectory of the tip head which has a recognized angle of the frontal plane cut to the horizon with successive build-up of rods.Changing the orientation in the space of the cut front surface of the cylindrical tip, taking into account the obtained mathematical model of correcting the trajectory of the head in the soil, allows to increase the span length to 100 m due to the proposed automated principle of correcting its movement.

고정자 비대칭 Tooth Tip과 회전자 Step Skew를 조합한 표면형 영구자석 모터의 코깅 토크 저감 설계

코깅 토크 저감은 높은 정밀 구동이 필요한 모터의 중요한 성능 인자이다. 따라서, 코깅 토크 저감을 위해 고정자 또는 회전자에 스큐가 주로 적용된다. 그러나, 스큐 방식은 제조 비용 증가하며, 이로 인해 의도치 않은 성능 열화가 나타나는 단점이 있다. 본 논문은 기존의 스큐 방식을 대신하여, 코깅 토크 및 토크리플 저감을 위해 회전자의 스큐 및 고정자의 비대칭 Tooth Tip를 적용한 설계를 제안한다. 연구 대상은 4단 step-skew를 적용한 기존의 회전자 모델에 대해, 2단 step skew를 적용한 회전자 및 비대칭 tooth tip을 적용한 모델이다. 제안 모델를 검증하기 위해, 유한요소법을 이용하여 코깅 토크, 역기전력 및 토크 리플을 비교한다.

Effects of circumferentially non-uniform clearance on the spanwise flow characteristics in a transonic compressor rotor

The circumferentially non-uniform clearance has significant effect on the overall performance and operation safety of high loading compressor rotors. However, both the variation rules and mechanism of flow characteristic in the circumferential, radial and streamwise directions caused by the asymmetric clearance are not fully clarified, which restricts the performance degradation assessment and rubust design of high loading compressors. Therefore, different types of asymmetric tip clearance were designed in this paper to reveal the circumferential fluctuation laws and induced mechanism of key characteristic parameters in full-channel domains of compressor rotor with circumferentially non-uniform clearance. It is shown that the circumferentially non-uniform clearance has less effect on the total pressure ratio and efficiency of compressor rotor, while it causes an obvious deterioration of the stall margin. Furthermore, the circumferentially non-uniform clearance causes the circumferential fluctuations of performance parameters, and the fluctuation amplitude has been affected by the eccentricity ratio and operating condition of rotor directly. In addition, the leakage flow originated from a single channel may pass through about three adjacent channels in rotor with uniform clearance, while it covers almost seven adjacent channels in the rotor with circumferentially non-uniform clearance. In consequence, it is precisely the difference of strength variation of leakage flow in tip region caused by the circumferential distributions of tip clearance that produces an alternated variation of low-velocity zone in rotor prototype and a concentrated distribution of low-velocity zone in the range of 270° to 360° of rotor with non-uniform clearance. Due to the serious blockage appearing in this range, the rotating stall of transonic rotor with circumferentially non-uniform clearance has occurred in advance, even with a maximum drop of 35.94% in stall margin.

A Bottom-Up Volume Reconstruction Method for Atom Probe Tomography.

This paper describes a reconstruction method for atom probe tomography based on a bottom-up approach accounting for (i) the final tip morphology (which is frequently induced by inhomogeneous evaporation probabilities across the tip surface due to laser absorption, heat diffusion effects, and inhomogeneous material properties), (ii) the limited (and changing) field of view, and (iii) the detector efficiency. The reconstruction starts from the final tip morphology and reverses the evaporation sequence through the pseudo-deposition of defined small reconstruction volumes, which are then stacked together to create the full three-dimensional (3D) tip. The subdivision in small reconstruction volumes allows the scheme to account for the changing tip shape and field of view as evaporation proceeds. Atoms within the same small reconstruction volume are reconstructed at once by placing atoms back onto their possible lattice sites through a trajectory-matching process involving simulated and experimental hit maps. As the ejected ion trajectories are simulated using detailed electrostatic modeling inside the chamber, no simplifications have been imposed on the shape of the trajectories, projection laws, or tip surface. We demonstrate the superior performance of our approach over the conventional reconstruction method (Bas) for an asymmetrical tip shape.

Plasmonic interference modulation for broadband nanofocusing

Abstract Metallic plasmonic probes have been successfully applied in near-field imaging, nanolithography, and Raman enhanced spectroscopy because of their ability to squeeze light into nanoscale and provide significant electric field enhancement. Most of these probes rely on nanometric alignment of incident beam and resonant structures with limited spectral bandwidth. This paper proposes and experimentally demonstrates an asymmetric fiber tip for broadband interference nanofocusing within its full optical wavelengths (500–800 nm) at the nanotip with 10 nm apex. The asymmetric geometry consisting of two semicircular slits rotates plasmonic polarization and converts the linearly polarized plasmonic mode to the radially polarized plasmonic mode when the linearly polarized beam couples to the optical fiber. The three-dimensional plasmonic modulation induces circumference interference and nanofocus of surface plasmons, which is significantly different from the nanofocusing through plasmon propagation and plasmon evolution. The plasmonic interference modulation provides fundamental insights into the plasmon engineering and has important applications in plasmon nanophotonic technologies.

Exploiting rotational asymmetry for sub-50\u2009nm mechanical nanocalligraphy

Nanofabrication has experienced extraordinary progress in the area of lithography-led processes over the last decades, although versatile and adaptable techniques addressing a wide spectrum of materials are still nascent. Scanning probe lithography (SPL) offers the capability to readily pattern sub-100 nm structures on many surfaces; however, the technique does not scale to dense and multi-lengthscale structures. Here, we demonstrate a technique, which we term nanocalligraphy scanning probe lithography (nc-SPL), that overcomes these limitations. Nc-SPL employs an asymmetric tip and exploits its rotational asymmetry to generate structures spanning the micron to nanometer lengthscales through real-time linewidth tuning. Using specialized tip geometries and by precisely controlling the patterning direction, we demonstrate sub-50 nm patterns while simultaneously improving on throughput, tip longevity, and reliability compared to conventional SPL. We further show that nc-SPL can be employed in both positive and negative tone patterning modes, in contrast to conventional SPL. This underlines the potential of this technique for processing sensitive surfaces such as 2D materials, which are prone to tip-induced shear or beam-induced damage.

Analytical grid generation and numerical assessment of tip leakage flows in sliding vane rotary machines

The research presents a new analytical grid generation methodology for computational fluid dynamics studies in positive displacement sliding vane rotary machines based on the user defined nodal displacement approach. This method is more inclusive than state of the art ones since it enables the investigation of a broader range of design configurations, such as single, double and multiple-acting vane machines with non-circular housing, slanted blade and asymmetric blade tip profiles. Node number and radial divisions of blade tip are the parameters that affect most the mesh quality. The method was validated against indicated pressure measurements on a rotary vane expander resulting in a confidence interval within 4.31%. The benchmark analysis showed that the proposed method is as accurate as the manual ANSYS ICEM one but more than 1500 times faster (111s instead of 48h to generate 360 grids). The paper further proposes a novel method to track the leakage flows at the blade tip gaps of vane machines through a post-processing routine in ANSYS CFD-Post based on rotating monitoring planes. The leakage assessment on the vane expander case study showed that a 10 μm gap between blade tip and the 76 mm stator led to a 0.06 unit increase of the expander filling factor.

MEASURING THE SOIL COMPACTION ZONE AND PRESSURE OF DEFORMED SOIL ON UNDERGROUND OBJECTS WITH AN ASYMMETRIC CYLINDRICAL TIP

At trenchless laying of engineering communications in soil the method of static puncture has received wide application at formation of a well. Power plants that implement it have small dimensions, which make them more effective in laying distribution engineering networks in tight urban conditions. Problem. The main disadvantages of the method are the low accuracy of the trajectory and the significant stress in the soil after its compaction, which can lead to the destruction of adjacent underground objects. The first disadvantage is solved by controlling the trajectory of the soil-piercing working body. To solve the second question, it is necessary to know and take into account the specifics of the formation of communication cavities in the soil with an asymmetric tip, which is used for this purpose. Goal. The aim of the work is to establish the regularity of the process of soil puncture by the soil-piercing working body with an asymmetric tip in the form of a cylinder cut at an angle. Methodology. The approaches adopted in the work to solve this goal are based on the theories of deep soil cutting, scientific foundations of soil mechanics, their normative physical and mechanical properties and the law of conservation of soil mass before and after compaction. Results. The calculated dependences for determining the size of the destructive zone from the elastic-plastic deformation of the soil during its puncture by an asymmetric tip with a frontal surface in the form of a beveled cylinder and the pressure of the deformed soil on underground objects are obtained. It is established that the maximum size of the destruction zone and its pressure on underground objects will occur in solid sand. With a tip diameter of 0.3 m, their values can reach 5 m and 0.245 MPa, respectively. Originality. The obtained regularities of soil puncture by a working body with an asymmetric tip in the form of a beveled cylinder made it possible to get an idea of the influence of its deformed state on adjacent communications depending on geometric parameters of the tip and physical and mechanical properties of soils. Practical value. The obtained results can be recommended in the design and determination of technological capabilities of installations for static soil puncture.

Determination of the regularities of the soil punching process by the working body with the asymetric tip

The presence of analytical dependencies describing the process of static soil puncture by a working body with a conical asymmetric tip is necessary to create installations with the ability to control the trajectory of the soil puncture. The paper considers the features of the process of interaction of an asymmetric conical tip with the ground. Analytical relationships were obtained to determine its reactions during a static puncture, the deviation of the head trajectory from a straight line, to determine the size of the soil compaction zone and the magnitude of the destructive force that acts on adjacent communications and other underground objects. It was found that with an increase in the value of the displacement of the top of the cone, for example, from its axis from 0.02 m to 0.08 m with a borehole diameter of 0.2 m, the value of soil resistance increases almost four times. The greatest resistance is achieved when piercing a hard sandy sand. It was found that with an increase in the displacement of the tip of the tip cone, the deviation of the trajectory increases. The piercing head achieves the greatest deviation from the straight trajectory of movement with a sharper cone and a greater asymmetric deviation of its top, and, for example, in hard sandy loam can be up to 0.17 m with a span of 10 m. It was found that the size of the soil destruction zone will be almost 1.8 times larger than the tip in the form of a symmetrical cone and reaches from 8 to 12 borehole diameters, depending on the type of soil. The maximum pressure on adjacent objects can reach from 0.06 MPa in hard-plastic clay to 0.09 MPa in hard sandy loam. The calculated dependences obtained for determining the power and technological parameters depending on the geometric dimensions of the asymmetric tip of the working body can be used to create installations with a controlled static puncture for use in the most common soil conditions.

Establishing the value of the deflection of the soil-piercing working body with an asymmetric tip when correcting the airway of movement

Trenchless laying of engineering communications is actively used in all countries of the world. Among the existing methods of formation of wells for the implementation of these technologies, the most popular is the method of ground penetration. The main disadvantage of this method is the poor accuracy of movement of the piercing head in the array. This requires constant adjustments to the trajectory of its movement. This process can be controlled by using a head with an asymmetrical tip and acting on it with translational and rotational motion. The transmission of these movements from the power unit by means of type-setting push rods. Therefore, it is important to choose a trajectory such that the deflection of the bar will be within the permissible stress range. If the bend goes beyond these limits, the rod may break and the puncture process will be interrupted. The conducted studies have established the regularities of the process of puncturing the soil with a head with an asymmetric tip in the form of an inclined flat surface. It has been established that the greatest deviation of the head from the action of the transverse component of the soil resistance force, which occurs when moving such a working body in the soil, will occur at an angle of inclination of the front surface of 25º, and the smallest deviation will occur at an angle of 55º. In addition, it was found that in heavy clay, deflection will occur almost 3 times worse than in a soup and 1.4 times worse than in a loam. It has been experimentally confirmed that at a distance of 10 m the puncture with a head with an inclined forehead surface in sandy loam was 40 mm, and in clay 20 mm. At an angle of inclination of 70º, a constant core of soil compaction is formed and the process of controlling the movement of the head stops.

Magnetic Needle Steering in Soft Phantom Tissue

Needle steering is a technology for guiding needles around sensitive internal obstacles in minimally invasive surgery. Traditional techniques apply rotation at the base of a needle with an asymmetric tip, enabling steering through the redirection of radial forces. Magnetic steering of catheters and continuum manipulators is another technology that allows steering of a shaft in the body. Both of these techniques rely on mechanical or manual shaft advancement methods. Needle steering has not achieved widespread clinical use due to several limitations: 1- buckling and compression effects in the shaft and needle rotation cause excessive tissue damage; 2- torsion effects on the shaft and needle deflection at tissue boundaries lead to difficulty in control; and 3- restricted radius of curvature results in limited workspace. Magnetically steered catheters and continuum manipulators also suffer from limited curvature and the possibility of buckling. This paper proposes a novel needle steering method empowered by electromagnetic actuation that overcomes all of the aforementioned limitations, making it a promising option for further study toward healthcare applications.

Asymmetrical Paleolithic wooden spear tips: Expediency or design?

Paleolithic wooden spears provide rare but unique insights into early hunting technology. Examples from Schöningen, Germany indicate that spear tips were sometimes asymmetrical. This asymmetry has previously been interpreted as evidence for planning depth. A more parsimonious explanation, however, is that asymmetrical tips could be more efficiently produced (i.e., took less time to make) than symmetrical ones. Here, we experimentally investigated two different manufacturing processes, producing asymmetrical and symmetrical spear tips, while also testing the influence of biometric factors on spear-tip manufacturing efficiency (measured by time). One group of experimental participants sliced the wooden stave into an asymmetrical shape (slicing on one side of the stave with a steel blade), while the other group created a symmetrical shape (slicing on multiple sides of the stave). Based on time taken, results demonstrated no significant difference in efficiency between symmetrical and asymmetrical spear-tip manufacture. Conversely, some biometric characteristics (specifically pinch strength) present a more dominant influence in explaining time variation. These results demonstrate that the asymmetrical tips at Schöningen were not merely a byproduct of maximizing efficiency during the manufacturing process, but rather are evidence of planning and the associated cognitive capacities of these later Middle Pleistocene hominins.

Vertical Alar Folding (VAF): A Useful Technique for Correction of Long and Concave Lateral Crura in Rhinoplasty.

The tripod theory explains the dynamics of the nasal tip, where surgery is difficult because of anatomic variations and pathologies and the various surgical possibilities. Abnormalities or weaknesses of the lateral crura can result in concavity in ala or alar collapse and cause aesthetic and functional impairments of the nose. Several tip plasty techniques and lateral crura modifications are used in rhinoplasty. To describe the vertical alar folding (VAF) technique for making modifications in the lateral crura (LC) and rotation of the tip. Included in the study were 83 patients (59 women, 24 men) undergoing rhinoplasty using VAF with the senior author as surgeon between 2013 and 2018. The mean age was 26.3years (range 18-47). Mean postoperative follow-up period was 26.7months (range 12-64). Patients who completed the 1-year postoperative period completed the rhinoplasty outcome evaluation (ROE) questionnaire. Outcome measures were performed at examinations, and preoperative and postoperative photographs of the patients were analyzed. In the span of 5years, no revision surgery was required for technique-specific reasons. In patients who had a droopy or asymmetric tip or long and concave lateral crura, we saw remarkable functional and aesthetic improvements with VAF. According to the ROE questionnaire, 90.3% (75 out of 83) of the patients were content with the aesthetic and functional results. VAF is a useful and effective method for modifying the LC and tip of the nose. VAF allowed for controlling the rotation and projection of the tip, changing the length of the lateral crus and nose with durability and smooth, symmetric contours, and correcting concavity of a lateral crus for better functioning and aesthetics. This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Mixed-mode crack propagation during needle penetration for surgical interventions

An accurate description of the penetration mechanics of flexible needles into target soft tissues is a complex task, including friction at the needle-tissue interface, large strains, non-predetermined penetration trajectories, fracture under mixed-mode loading and so on. In the present work, a finite element algorithm is employed to simulate the two-dimensional deep penetration of a flexible needle in a soft elastic material. The fracture process of the target material during penetration is described by means of a cohesive zone model, with a suitable mixed-mode criterion for determining the propagation direction of the crack. To illustrate the potential of the numerical algorithm, we have performed some simulations of the insertion of a flexible needle with an asymmetric tip, and the results are presented in terms of force-penetration curves as well as of the obtained penetration paths in the target tissue.