Number Of Struts Research Articles

Design and Characterisation of a Novel Z-Shaped Inductor-Based Wireless Implantable Sensor for Surveillance of Abdominal Aortic Aneurysm Post-Endovascular Repair.

An abdominal aortic aneurysm (AAA) is a dilation of the aorta over its normal diameter (> 3 cm). The minimally invasive treatment adopted uses a stent graft to be deployed into the aneurysm by a catheter to flow blood through it. However, this approach demands frequent monitoring using imaging modalities that involve radiation and contrast agents. Moreover, the multiple follow-ups are expensive, time-consuming, and resource-demanding for healthcare systems. This study proposes a novel wireless implantable medical sensor (WIMS) to measure the aneurysm growth after the endovascular repair. The proposed sensor is composed of a Z-shaped inductor, similar to a stent ring. The proposed design of the sensor is explored by investigating the inductance, resistance, and quality factor of different possible geometries related to a Z-shaped configuration, such as the height and number of struts. The study is conducted through a combination of numerical simulations and experimental tests, with the assessment being carried out at a frequency of 13.56 MHz. The results show that a higher number of struts result in higher values of inductance and resistance. On the other hand, the increase in the number of struts decreases the quality factor of the Z-shaped inductor due to the presence of high resistance from the inductor. Moreover, it is observed that the influence of the number of struts present in the Z-shaped inductor tends to decrease for larger radii. The numerical and experimental evaluation concludes the ability of the proposed sensor to measure the size of the aneurysm.

Numerical Research of Flame Propagation Process in a Supersonic Combustor with Multi-Strut

ABSTRACT The flame processes and the influence of different factors on the cross flame propagation width in a supersonic combustor equipped with multi-strut fueled with kerosene were analyzed to deepen the understanding of supersonic flame characteristics. Under the conditions of T t = 1680K, P t = 1.64Mpa, and Ma = 2.7, the numerical calculations using the multi-step combustion reaction mechanism were carried out. The mixing performance and flame propagation width could be improved by increasing the number of struts. In the multi-strut injection method, the cross flame was observed outside the central flame. The mechanism of cross flame formation was revealed. The establishment of the cross flame had a maximum spacing requirement between injection struts, but this limit could be expanded by the high temperature zone formed by the narrow-distance injection strut. The effects of igniter energy and ignition strut equivalence ratio on the flame diffusion process were studied. Then the boundary conditions required for the cross flame propagation were obtained. The results of this study are highly significant for enhancing the performance of large-scale supersonic combustors in the future.

Effect of strut microstructure on multiscale radiation properties of porous foams

Porous materials, widely used in engineering due to their excellent physical properties, have significant engineering and academic research value in their mechanism of radiation heat transfer. Micro-cellular foams are composed of a large number of struts and walls with micro-scale radiation effect, making it difficult to analyze the influence of strut micro-structure on radiation properties. In this study, the radiation parameters of the curved triangular prism-shaped struts are calculated using the finite element electromagnetic method, and the influence of the strut micro-structure parameters and the macroscopic parameters of the foam on the radiation characteristics is analyzed. The results demonstrate that the radiation properties of the equal-volume cylinder model, compared to the double-layer cylinder model, are closer to those of the curved triangular prism struts. The incidence angle has a negligible impact on the radiation parameter deviation of the struts. It is difficult to ignore the radiation parameter deviation of concave-curved triangular prism-shaped struts. The macroscale radiation properties of the foam are significantly influenced by the microscale radiation properties of the struts in the situation of low porosity, large pore size, and high strut volume ratio.

Numerical simulation of flame propagation characteristics in a strut-equipped supersonic combustor fueled with liquid kerosene

The flame propagation characteristics and multiple influencing factors of the flame width of the strut-equipped supersonic combustor fueled by liquid kerosene were observed to deepen understanding of the combustion characteristics. A series of numerical simulations using a multi-step reaction combustion mechanism were performed under the condition of Tt= 1680K, Pt = 1.64Mpa, and Ma = 2.7. The flame propagation process at the tail of the strut could be divided into three regions by the change of flame width: initial propagation region, contraction region, and re-propagation region. The fitting formulas of flame width in the initial propagation zone and re-propagation zone were obtained. The mechanism of igniter power on flame width was revealed, which broadens the propagation width of the flame by increasing the degree of local thermal choking and the reactivity of particles. The flame propagation processes under different number of struts were also studied. Under the multi-strut injection method, a cross flame zone was generated outside the center flame, and the flame propagation width was increased significantly. The main driving force of flame propagation in these two flame regions was obtained. The results of this paper are beneficial for the future performance optimization of the supersonic combustors using liquid kerosene fuel.

Optimizing inferior vena cava filter design: A computational fluid dynamics study on strut configuration for enhanced hemodynamic performance and thrombosis reduction

Background and objectiveInferior vena cava filters have been shown to be effective in preventing deep vein thrombosis and its secondary complication, pulmonary embolism, thereby reducing the high mortality rate. Although inferior vena cava filters have evolved, specific complications like inferior vena cava thrombosis-induced deep vein thrombosis worsening and recurrent pulmonary embolism continue to pose challenges. This study analyzes the effects of geometric parameter variations of inferior vena cava filters, which have a significant impact on the thrombus formation inside the filter, the capture, dissolution, and hemodynamic flow of thrombus, as well as the shear stress on the filter and vascular wall. MethodsThis study used computational fluid dynamic simulations with the carreau model to investigate the impact of varying inferior vena cava filter design parameters (number of struts, strut arm length, and tilt angle) on hemodynamics. ResultsRecirculation and stagnation areas due to flow velocity and pressure, along with wall shear stress values, were identified as key factors. It is important to find a balance between wall shear stress high enough to aid thrombolysis and low enough to prevent platelet activation. The results of this paper show that the risk of platelet activation and thrombus filtration may be lowest when the wall shear stress of the filter ranges from 0 to 4 [Pa], minimizing stress concentration within the filter. Conclusion16 arm struts with a length of 20 mm and a tilt angle of 0° provide the best balance between thrombus capture and minimization of hemodynamic disturbance. This configuration minimizes the size of the stagnation and recirculation zones while maintaining sufficient wall shear stress for thrombus dissolution.

Ni–Ti multicell interlacing Gyroid lattice structures with ultra-high hyperelastic response fabricated by laser powder bed fusion

Ni–Ti alloys based on triple-periodic minimal surface lattice metamaterials have great application potential. In this work, the triply periodic minimal surface (TPMS) lattice structures with the same volume fraction from a normal Gyroid lattice to an octuple interlacing Gyroid lattice were prepared by the laser powder bed fusion (LPBF) technique. The influence of the interlacing-cell number on manufacturability, uniaxial compression mechanical behaviors, and hyperelastic responses of Ni–Ti lattice structures are analysed by experiments. The stress distributions and fracture mechanism of multicell interlacing lattice structures are illustrated by the finite element method. The obtained results reveal that when the volume fraction is the same, the specific surface area of the lattice structure increases with increasing interlacing-cell number, and the curvature radius of the single-cell strut reduces, which leads to the decrease in the manufacturability of the lattice structure. Meanwhile, the diameter of the single cell strut decreases, and the stress it can bear decreases, which leads to a decline in the compressive mechanical property of the lattice structure. However, the number of struts increases with the increase of interlacing cells, which makes the stress distribution of the lattice structure more uniform. The cyclic compression results indicate that with increasing interlacing-cell number, the proportion of the hyperelastic recoverable strain increases, and the residual strain in the cyclic compression test decreases. For the lattice structure with a chiral arrangement of single cells, the manufacturability, compressive mechanical properties, and hyperelasticity are comparable to those with a normal arrangement. Notably, the Ni–Ti Gyroid TPMS lattice structures have superior hyperelasticity properties (98.87–99.46 % recoverable strain).

Multi-objective design optimization of stent-grafts for the aortic arch

Complications of thoracic endovascular aortic repair are closely related to the mechanical properties of implanted stent-grafts. Compared with straight vessels, the complex morphology of aortic arch imposes strict requirements on stent-graft properties. This study designed and verified an aortic stent-graft by optimizing a specially constructed commercial descending stent-graft. The main structural parameters including strut height, strut number, strut radius, wire diameter, and graft thickness were set as the design variables. The essential mechanical properties (flexibility and radial support force) of stent-grafts relevant to the mentioned variables were selected as objective functions. Surrogate model and multi-objective genetic algorithms were adopted to implement the optimization process. Finally, the optimized stent-graft was virtually implanted into an ideal aortic arch to verify its suitability. The optimization was completed after 16 iterations, demonstrating that the optimization method used in this study was efficient. The results showed that the flexibility of the near-optimal stent-graft improved over 50% and the radial support force was extremely close to that of the original design. Compared with the original design, the sealing effect of the optimized stent-graft was significantly improved. The results of this study provide guidelines and a feasible method for designing aortic arch stent-grafts.

Study on the relationship between the length of mixing layer and the characteristic scale of mixing layer in multi-strut ejector

The flow structure of the multi-strut ejector based on jet segmentation has an obvious relationship with the transverse characteristic scale of the jet. Therefore, this paper studies the relationship between jet transverse characteristic size and mixing layer. Through the simulation of multi-strut ejectors with different number of struts, the development of mixing layer in the mixing process of jets with different transverse characteristic sizes is compared under the same boundary conditions. It is concluded that when there is no obvious coupling effect between the mixing layer and the shock & expansion wave, there is a linear relationship between the transverse characteristic scale of the jet and the mixing length of the flow direction, and the jet mixing with different transverse characteristic scales is consistent. When the shockwaves and expansion waves are strongly coupled with the mixing layer, the linear relationship between the jet transverse characteristic scale and the mixing layer length is not strong.

Evaluation of stent effect and thrombosis generation with different blood rheology on an intracranial aneurysm by the Lattice Boltzmann method

Treatment of intracranial aneurysms with flow-diverting stents prevents rupture by reducing blood flow and creating thrombosis within the aneurysm. This paper aims to assess the hemodynamic effect of placing stents with different struts (0, 3, 5, 7 struts) on intracranial aneurysms and to propose a simple prediction model of thrombosis zone without any further computational cost. Lattice Boltzmann method with different rheological models (Newtonian, Carreau-Yasuda, KL) of blood are used to study the hemodynamic effect of flow-diverting stents in the aneurysm. Pulsatile flow boundary conditions were applied in the inlet of the artery. The average Reynolds number was resulting Re=111. The Lagrangian tracking of the particle was developed to assess the intra-aneurysmal blood stagnation. To predict the probable thrombose zone induced by flow-diverting stents, the shear rate threshold is utilized to determine the nodes of fluid to clot. The results show that the flow patterns into the aneurysmal sac develop a vortex, decreasing after stent placement until disappearance for the stent with seven struts (porosity 71.4%). Velocity, shear rate, shear stress, trajectory, path length, and occlusion rate are compared before and after stent placement. These parameters decrease inversely with the porosity of the stent. The three models yield a closes result of the (velocity, shear rate, occlusion rate). Tracking the fluid-particle trajectory shows that the length of the particle paths decreases with the number of struts causing fluid to slow down and increase, consequently, the residence time into the sac. The flow-diverting stents placement cause the reduction of dynamic flow within aneurysm. The reduction effect is almost the same below five struts (80% of porosity). The results show that, if our objective is restricted to estimating the hemodynamic effect, measured by (velocity, shear rate, occlusion rate), the differences between rheological behavior models are, practically, not significant, and the models can be used indifferently.

Effects of design parameters on the static responses of two-way beam string structure

A two-way beam string structure is composed of upper beam and two different cables, namely, sagging and arch-shaped cables. It is designed for structural members under bi-directional loads because the maximum stress and displacement can dramatically reduced. In this study, a parametric study for this structure is presented to provide optimal design parameters, which include number of struts and curvature of cable. Numerical examples are implemented in the ABAQUS finite element package to validate and then study the effects of the number of struts, deflections and stresses as well relationships of ultimate loads for various cable curvatures. Besides, the stress sharing ratio of top/bottom of the beam and the sagging cable under positive and negative pressure are investigated.

Long-term safety and absorption assessment of a novel bioresorbable nitrided iron scaffold in porcine coronary artery.

This study aimed to investigate the long-term biocompatibility, safety, and degradation of the ultrathin nitrided iron bioresorbable scaffold (BRS) in vivo, encompassing the whole process of bioresorption in porcine coronary arteries. Fifty-two nitrided iron scaffolds (strut thickness of 70 μm) and 28 Vision Co–Cr stents were randomly implanted into coronary arteries of healthy mini-swine. The efficacy and safety of the nitrided iron scaffold were comparable with those of the Vision stentwithin 52 weeks after implantation. In addition, the long-term biocompatibility, safety, and bioresorption of the nitrided iron scaffold were evaluated by coronary angiography, optical coherence tomography, micro-computed tomography, scanning electron microscopy, energy dispersive spectrometry and histopathological evaluations at 4, 12, 26, 52 weeks and even at 7 years after implantation. In particular, a large number of struts were almost completely absorbed in situ at 7 years follow-up, which were first illustrated in this study. The lymphatic drainage pathway might serve as the potential clearance way of iron and its corrosion products.

Infill topology and shape optimization of lattice‐skin structures

AbstractLattice‐skin structures composed of a thin‐shell skin and a lattice infill are widespread in nature and large‐scale engineering due to their efficiency and exceptional mechanical properties. Recent advances in additive manufacturing, or 3D printing, make it possible to create lattice‐skin structures of almost any size with arbitrary shape and geometric complexity. We propose a novel gradient‐based approach to optimizing both the shape and infill of lattice‐skin structures to improve their efficiency further. The respective gradients are computed by fully considering the lattice‐skin coupling while the lattice topology and shape optimization problems are solved in a sequential manner. The shell is modeled as a Kirchhoff–Love shell and analyzed using isogeometric subdivision surfaces, whereas the lattice is modeled as a pin‐jointed truss. The lattice consists of many cells, possibly of different sizes, with each containing a small number of struts. We propose a penalization approach akin to the SIMP (solid isotropic material with penalization) method for topology optimization of the lattice. Furthermore, a corresponding sensitivity filter and a lattice extraction technique are introduced to ensure the stability of the optimization process and to eliminate scattered struts of small cross‐sectional areas. The developed topology optimization technique is suitable for nonperiodic, nonuniform lattices. For shape optimization of both the shell and the lattice, the geometry of the lattice‐skin structure is parameterized using the free‐form deformation technique. The topology and shape optimization problems are solved in an iterative, sequential manner. The effectiveness of the proposed approach and the influence of different algorithmic parameters are demonstrated with several numerical examples.

Electrical Heating Performance of Graphene/PLA-Based Various Types of Auxetic Patterns and Its Composite Cotton Fabric Manufactured by CFDM 3D Printer.

To evaluate the electrical heating performance by auxetic pattern, re-entrant honeycomb (RE), chiral truss (CT), honeycomb (HN), and truss (TR), using graphene/PLA (Polylactic acid) filament, were manufactured by CFDM (conveyor fused deposition modelling) 3D printer. In addition, HN and TR, which was indicated to have an excellent electrical heating property, were selected to verify the feasibility of applying fabric heating elements. The result of morphology was that the number of struts constituting the unit cell and the connected points were TR < HN < CT < RE. It was also influenced by the surface resistivity and electrical heating performance. RE, which has the highest number of struts constituting the unit cell and the relative density, had the highest value of surface resistivity, and the lowest value was found in the opposite TR. In the electrical heating performance of samples, the heat distribution of RE was limited even when the applied voltage was increased. However, HN and TR were diffused throughout the sample. In addition, the surface temperature of RE, CT, HN, and TR was about 72.4 °C, 83.1 °C, 94.9 °C, and 85.9, respectively as applied at 30 V. When the HN and TR were printed on cotton fabric, the surface resistivity of HN/cotton and TR/cotton was about 103 Ω/sq, which showed conductive material. The results of electrical heating properties indicated that the heat distribution of HN/cotton showed only in the region where power was supplied, but the TR/cotton was gradually expanded and presented stable electric heating properties. When 30 V was applied, the surface temperature of both samples showed more than 80 °C, and the shape was maintained stably due to the high thermal conductivity of the cotton fabric. Therefore, this study ensured that HN and TR show excellent electrical heating performance among four types of auxetic patterns with continuity.

Biodegradable performance of PLA stents affected by geometrical parameters: The risk of fracture and fragment separation

Biodegradable endovascular stents have been claimed to be reliable candidates for implantation devices used in treating cardiovascular diseases since they reduce the long-term side effects on the human biological system. It is aimed in this study to investigate the effect of geometrical parameters on the degradation behavior of poly (lactic acid) stents in term of strut fracture and fragment separation. In this regard, various structural geometry of the PLA stents was simulated in a stenosed artery using finite element method. For predicting the PLA degradation, a computational model was prepared by which the influence of stents design on their radial strength and fracture was investigated. Using a laboratory-scale designed bioreactor, the PLA fibers degradation was evaluated to calibrate the material parameters and verify the simulation method. Simulation results demonstrated that the geometrical parameters, i.e., number of struts, curves radius and stent cells shape, strongly affect the degradation behavior. The results indicated that the smooth design leads to uniform degradation in the whole stent and decreases the danger of stent fragments separation. It was shown that the maximum degradation rate of the stents with rounded curves was one-third of the models with sharp corners.

Nanonetwork Thermosets from Templated Polymerization for Enhanced Energy Dissipation.

Herein, we aim to develop a facile method for the fabrication of mechanical metamaterials from templated polymerization of thermosets including phenolic and epoxy resins using self-assembled block copolymer, polystyrene-polydimethylsiloxane with tripod network (gyroid), and tetrapod network (diamond) structures, as templates. Nanoindentation studies on the nanonetwork thermosets fabricated reveal enhanced energy dissipation from intrinsic brittle thermosets due to the deliberate structuring; the calculated energy dissipation for gyroid phenolic resins is 0.23 nJ whereas the one with diamond structure gives a value of 0.33 nJ. Consistently, the gyroid-structured epoxy gives a high energy dissipation value of 0.57 nJ, and the one with diamond structure could reach 0.78 nJ. These enhanced properties are attributed to the isotropic periodicity of the nanonetwork texture with plastic deformation, and the higher number of struts in the tetrapod diamond network in contrast to tripod gyroid, as confirmed by the finite element analysis.

Auto Strut: a novel smart robotic system for external fixation device for bone deformity correction, a preliminary experience.

PurposeSeveral hexapod external fixators are used in the treatment of bone fracture and deformity corrections. One characteristic of all of them is the requirement for manual adjustment of the fixator struts. The purpose of this study was to introduce a novel robotic system that executes automatic adjustment of the struts.MethodsTen patients were treated for various bone deformities using a hexapod external fixator with the Auto Strut system. This new system automatically adjusts the fixator struts according to a hexapod computer-assisted correction plan. During each visit, the progress of the correction was assessed (clinically and radiographically) and reading of the strut scale numbers was performed and compared with the original treatment plan.ResultsAll patients completed treatment during the follow-up period, achieving all planned correction goals, except from one patient who switched to manual struts due to personal preference. The device alarm system was activated once with no device-related adverse events. Duration of distraction ranged between ten and 90 days with a distraction index ranging between eight and 15 days/cm. Regenerate consolidation time between one and seven months. In total, 48 struts of eight patients were recorded and analyzed. In all, 94% of the final strut number readings presented a discrepancy of 0 mm to 1 mm between planned and actual readings, indicating high precision of the automatic adjustment.ConclusionThis study presents preliminary results, showing that Auto Strut can successfully replace the manual strut adjustment providing important advantages that benefit the patient, the caregiver and the surgeon.Level of EvidenceLevel II

Memory-Efficient Modeling and Slicing of Large-Scale Adaptive Lattice Structures

Abstract Lattice structures have been widely used in various applications of additive manufacturing due to its superior physical properties. If modeled by triangular meshes, a lattice structure with huge number of struts would consume massive memory. This hinders the use of lattice structures in large-scale applications (e.g., to design the interior structure of a solid with spatially graded material properties). To solve this issue, we propose a memory-efficient method for the modeling and slicing of adaptive lattice structures. A lattice structure is represented by a weighted graph where the edge weights store the struts' radii. When slicing the structure, its solid model is locally evaluated through convolution surfaces and in a streaming manner. As such, only limited memory is needed to generate the toolpaths of fabrication. Also, the use of convolution surfaces leads to natural blending at intersections of struts, which can avoid the stress concentration at these regions. We also present a computational framework for optimizing supporting structures and adapting lattice structures with prescribed density distributions. The presented methods have been validated by a series of case studies with large number (up to 100M) of struts to demonstrate its applicability to large-scale lattice structures.

Numerical insights into the determinants of stent performance for the management of aneurysm with a visceral vessel attached

As the factors affecting the efficacy of the bare-metal stent in the treatment of aneurysm with a visceral vessel attached were not fully understood, we aimed to discuss the effects of different characteristics of the stent on the hemodynamics and flexibility in the treatment of the aneurysm. Single-layer (with different strut widths) and multi-layer (with a different number of struts) stent models divided into three porosity groups, with porosities of 72.3, 60.5, and 52.4%, were modeled for a comparison of their hemodynamic isolation and flexibility performance via computational fluid dynamics and finite element methods. The velocity and timeaveraged wall shear stress decreased more noticeably with multi-layer stent interventions. A higher oscillatory shear index and relative residence time occurred at the aneurysmal sac wall after multi-layer stents were employed. Time-averaged wall shear stress on the aneurysmal wall decreased with an increase in the number of struts or a decrease in pore size, but oscillatory shear index and relative residence time increased as the number of struts increased or the pore size decreased. Besides, all stents affect the branch patency slightly. In the bending test, when the porosity exceeded 60.5%, multi-layer stents were more flexible. The number of struts or pore size of stent dominated the isolation in the management of the aneurysm and affected the flexibility significantly when the porosity was below 60.5%. These findings may contribute to the special design of the stent in the treatment of such types of aneurysms.

Thoracic aorta stent grafts design in terms of biomechanical investigations into flexibility.

The present study aimed to design and optimize thoracic aorta stent grafts (SGs) based on the influence of geometric parameters on flexibility and durability. Five geometric parameters were selected, including strut height, strut number, strut radius, wire diameter, and graft thickness. Subsequently, 16 finite element (FE) models were established with an orthogonal design consisting of five factors and four levels. The influences of a single factor and all the geometric parameters' influence magnitude on the device flexibility were then determined. The results showed that all the other parameters had an opposite effect on global and local flexibility except for the wire diameter. The graft thickness exhibited the most remarkable impact on the global flexibility of SGs, while the strut radius influenced flexibility slightly. However, for the local flexibility analysis, the graft thickness became the least significant factor, and the wire diameter exerted the most significant influence. The SG with better global flexibility can be guided easily in the tortuous vessels, and better local flexibility improves the sealing effect between the graft and aortic arch. In conclusion, this study's results indicated that these geometric parameters exerted different influences on flexibility and durability, providing a strategy for designing thoracic aorta SGs, especially for the thoracic aortic arch diseases.

Morphological evolution of silica scales in the freshwater genus Synura (Stramenopiles).

A high degree of morphological variability is expressed between the ornately sculptured siliceous scales formed by species in the chrysophycean genus, Synura. In this study, we aimed to uncover the general principles and trends underlying the evolution of scale morphology in this genus. We assessed the relationships among thirty extant Synura species using a robust molecular analysis that included six genes, coupled with morphological characterization of the species-specific scales. The analysis was further enriched with addition of morphological information from fossil specimens and by including the unique modern species, Synura punctulosa. We inferred the phylogenetic position of the morphologically unique S.punctulosa, to be an ancient Synura lineage related to S.splendida in the section Curtispinae. Some morphological traits, including development of a keel or a labyrinth ribbing pattern on the scale, appeared once in evolution, whereas other structures, such as a hexagonal meshwork pattern, originated independently several times over geologic time. We further uncovered numerous construction principles governing scale morphology and evolution, as follows: (i) scale roundness and pore diameter decreased during evolution; (ii) elongated scales became strengthened by a higher number of struts or ribs; (iii) as a consequence of scale biogenesis, scales with spines possessed smaller basal holes than scales with a keel and; and (iv) the keel area was proportional to scale area, indicating its potential value in strengthening the scale against breakage.