Reconstruction and analysis of K-Clip surgery process based on finite element method / 中国胸心血管外科临床杂志

@#Objective     To investigate the effects of different types of tricuspid regurgitation, implantation positions, and device models on the treatment outcomes of K-Clip for tricuspid regurgitation using numerical simulations. Methods     Three-dimensional reconstruction of the heart model was performed based on CT images. Two different regurgitation orifices were obtained by modifying the standard parameterized tricuspid valve leaflets and chordae tendineae. The effects of different K-Clip models at different implantation positions (posterior leaflet midpoint, anterior-posterior commissure, anterior leaflet midpoint, posterior septal commissure) were simulated using commercial explicit dynamics software Ls-Dyna. Conclusion     For the two types of regurgitation in this study, clipping at the posterior leaflet midpoint resulted in a better reduction of the regurgitation orifice (up to 75% reduction in area). Higher clamping forces were required for implantation at the anterior leaflet midpoint and posterior septal commissure, which was unfavorable for the smooth closure of the clipping components. There was no statistical difference in the treatment outcomes between the 18T and 16T K-Clip components, and the 16T component required less clamping force. Therefore, the use of the 16T K-Clip component is recommended.

Mathematical modelling approach of the study of Ebola virus disease transmission dynamics in a developing country

Background: Ebola Virus causes disease both in human and non-human primatesespecially in developing countries. In 2014 during its outbreak, it led to majority of deaths especially in some impoverished area of West Africa and its effect is still witnessed up till date. Materials and Methods:We studied the spread of Ebola virus and obtained a system of equations comprising of eighteen equations which completely described the transmission of Ebola Virus ina population where control measures were incorporated and a major source of contacting the disease which is the traditional washing of dead bodies was also incorporated. We investigated the local stability of the disease-free equilibrium using the Jacobian Matrix approach and the disease-endemic stability using the center manifold theorem. We also investigated the global stability of the equilibrium points using the LaSalle's Invariant principle.Results: The result showed that the disease-free and endemic equilibrium where both local and globally stable and that the system exhibits a forward bifurcation.Conclusions: Numerical simulations were carried out and our graphs show that vaccine and condom use is best for susceptible population, quarantine is best for exposed population, isolation is best for infectious population and proper burial of the diseased dead is the best to avoid further disease spread in the population and have quicker and better recovery.

Effects of Human Postures on Flow Characteristics in Iliac Vein Compression Syndrome / 医用生物力学

Objective To investigate effects of human postures on flow characteristics of iliac vein compression syndrome. Methods The numerical model of iliac vein was reconstructed from CT images of a typical patient with pelvic-type iliac vein compression syndrome with collateral veins. Based on the computational fluid dynamics method, the non-Newtonian model and the porous media model were adopted to describe effects of abnormal structures on blood flow and acquire the wall shear stress and pressure of iliac vein. The discrete phase model was used to study the residence conditions of erythrocytes under three human postures. Results The pressure gradient at two ends of the compressive region was lowest under lying state, while the iliac vein showed a high pressure under sitting and walking states. The local maximum wall shear stresses under three postures were found at narrow segment of the collateral vein and convergence region of two flows of right iliac vein. The maximum shear stress was largest under lying state and smallest under sitting state. The blood residence time of 52.2 s in the left iliac vein was the longest under sitting state. The residence time of 14.8 s was shortest under lying state. The blood residence time was 23.8 s under walking state. Conclusions Porous media model used to simulate the effect of abnormal structures was highly consistent with the angiography data. The venous hypertension under sitting and walking states was consistent with the clinical results, and the lying state could relieve the hypertensive condition. In terms of wall shear stress and blood residence time in iliac vein, the continual change between three human postures would cause endothelial damage and blood flow stasis alternately, thus increase the risk of thrombosis.

Influences of Morphological Characteristics of Modular Inner Branched Stent Graft on Hemodynamic Performance of Stent / 医用生物力学

Objective To study the effect of morphological characteristics of modular inner branched stent graft (MIBSG) on hemodynamic performance of postoperative aortic arch based on parameterized MIBSG model. Methods The fluid-structure interaction model of blood-MIBSG coupling performance was solved, and the effects of stent branch angles, stent diameters on hemodynamic characteristics were analyzed. Results With the increase of angles between branch stent and aortic arch stent, blood flow within the branch decreased, but the stress and displacement increased. With the decrease of stent diameters, blood flow perfusion decreased significantly, but the stress and displacement increased first, and then decreased. Conclusions The morphological changes of MIBSG not only have an impact on blood perfusion rate of branch stent, but also affect the stress exerted on stent and the corresponding displacement. Before application in clinic treatment of aortic arch diseases, the movement and torsion of MIBSG should been taken into full account in operation plan according to the actual situation.

Structure Design and Finite Element Analysis on Patch in Intraventricular Tunnel / 医用生物力学

ObjectiveT o explore the influence of patch shape for intraventricular tunnel (IVT) construction on biomechanical performance of the double outlet right ventricle after correction. Methods Based on the idealized IVT model, a two-dimensional IVT patch was designed. Six groups of patch models with the rhombic long-to-short axis ratio of 1∶0.625, 1∶0.3, 1∶0.2, 1∶0.15, 1∶0.125, 1∶0.1 were established according to the difference between the long and short axis of the rhombus patch in the turning part, and finite element analysis method was used to numerically simulate the process of stitching, holding and propping up the patch into a three-dimensional (3D) IVT model. Results The maximum stresses on suture line of 6 patch models were mainly concentrated at acute-angle corners of the rhombus. As rhombic long-to-short axis ratio of the patch increased, the maximum stress of the IVT suture line first decreased and then increased, and the volume showed an increasing trend. The pressure difference between two ends of the tunnel first decreased and then increased. The patch with the long-to-short axis ratio of 1∶0.15 had a uniform surface stress distribution, and the maximum stress on the suture line was the smallest. Meanwhile the right ventricular volume was less encroached on, and the pressure difference at both ends of the tunnel was small. Conclusions The IVT shape can influence stresses of suture line, the right ventricle volume and the pressure difference of IVT with non-monotonic variations. The suture effect of the patch with the long-to-short axis ratio of 1∶0.15 is relatively better among the constructed models.

Effect of a delay mode of a ventricular assist device on hemodynamics of the cardiovascular system / 生物医学工程学杂志

The implantation of biventricular assist device (BiVAD) is more challenging than that of left ventricular assist device for the interaction in the process of multiple input and output. Besides, ventricular assist device (VAD) often runs in constant speed (CS) mode in clinical use and thus BiVAD also faces the problems of low pulsation and imbalance of blood volume between systemic circulation and pulmonary circulation. In this paper, a delay assist mode for a VAD by shortening the support time of VAD was put forward. Then, the effect of the delay mode on cardiac output, pulsation and the function of the aortic valve was observed by numerical method and the rules of hemodynamics were revealed. The research showed that compared with VAD supported in CS mode, the VAD using delay mode in systolic and diastolic period proposed in this paper could meet the demand of cardiac output perfusion and restore the function of the arterial valves. The open ratio of aortic valve (AV) and pulmonary valve (PV) increased with the time set in delay mode, and the blood through the AV/PV helped to balance the left and the right cardiac volume. Besides, delay mode also improved the pulsation index of arterial blood flow, which is conducive to the recovery of the ventricular pulse function of patients.

Numerical Simulation of Aerosol Transport in Deep Alveolus during Atomization Therap / 医用生物力学

Objective Based on computational fluid dynamics (CFD) method, the air and aerosol transport in a single alveolus were simulated to study the characteristics of airflow and aerosol transport in deep alveolus. Methods A long straight duct with a hemispherical wall at one end which had periodic expansion/contraction were regarded as simplified approximation of a single alveolus. Based on this, a two-dimensional (2D) mathematical model was established.The Euler-Euler method was used to solve the transport equations of airflow and aerosol particles in the alveolus considering air diffusion along the hemisphere boundary. Results The composition ratio of the air in the duct changed in a stable periodic way during the whole breathing process.The aerosol transport in the duct mainly depended on the particle diffusion coefficient. The advection transport had only a small effect on it. The diffusion velocity and depth of aerosol increased when the particle size decreased, especially when the particle size was smaller than 4 μm. The increase of respiratory frequency and amplitude could significantly improved the transport capacity of aerosol particles. Conclusions In atomization treatment, aerosol particles with smaller particle size have better transportation and curative efficacy. Deep breathing should be encouraged to improve particle transport.

Effects of Fixator Stiffness on Healing of Fracture with Different Types / 医用生物力学

Objective To systematically explore the change of fixator stiffness (0.05-7.50 kN/mm) on healing effects of seven different types of fractures (A1: simple spiral, A2: simple oblique, A3: simple transverse; B2: wedge spiral, B3: wedge fragmented; C2: complex segment, C3: complex irregular) under the OTA/AO fracture classification. Methods Taking intramedullary nail fixation of long bone fracture as research objective, based on strain-regulated tissue differentiation theory, and combined with fuzzy logic algorithm and finite element analysis, the process of fracture healing was numerically simulated. Results Moderate fixator stiffness (1.5-2.5 kN/mm) shortened the healing time while ensuring recovery of biomechanical performance of the fractured bone. However, the appropriate fixator stiffness corresponding to each fracture type was different. The sensitivity of healing effects to change of fixator stiffness was also different. For type A fracture, when fixator stiffness was 1.5 kN/mm, optimal biomechanical recovery of the fractured site could be obtained, while the change in fixator stiffness had a large impact on healing effect. For type B and C fractures, when fixator stiffness was above 1.5 kN/mm, the change in fixator stiffness had no significant effects on recovery of biomechanical performance. Conclusions Fracture healing is affected by both fixator stiffness and fracture types. For treating fractures in clinic, the selection of fixators should carefully take fracture types into account.

Hemodynamic Analysis of Redissection after Endovascular Repair for One Stanford Type B Aortic Dissection Case / 医用生物力学

Objective Based on hemodynamic analysis, to investigate the cause of distal re-entry tear in Stanford type B aortic dissection after thoracic endovascular aortic repair (TEVAR).Methods A patient with type B aortic dissection was reexamined regularly with computed tomography angiography (CTA) at 1st month, 6th month, 12th month and 24th month after TEVAR. Based on the CTA images in each period, three-dimensional (3D) aorta models were reconstructed to perform morphological analysis and hemodynamic simulation.Results Compared with the diameter at 1st month after TEVAR, the diameter of true lumen at 12 months after TEVAR increased by 1.8 times and the global distortion of aorta increased by 16.67%. At postoperative 1st, 6th and 12th month, the maximum blood velocities at the new entry tear in systole were 69.6%, 33.7% and 92.1% higher than the average ones at distal landing zone, and the maximum wall shear stresses (WSSs) were 2.52, 2.32 and 3.52 times of the average WSSs respectively. In addition, the maximum time-averaged WSS (TAWSS) at 1st, 6th and 12th month after TEVAR were 1.88, 2.53 and 3.62 times of the mean TAWSS respectively.ConclusionsThe morphology of the aorta remodeled after TEVAR, and a sudden change in the diameter of true lumen occurred at distal anchoring zone and continued to increase. As a result, the blood flow velocity in this area accelerated, and the intima was continuously exposed to high WSS, leading to the redissection.

Compression Properties of Fat Layer under Impact Loading / 医用生物力学

Objective To study dynamic compression performance of adipose tissues, so as to further reveal the damage mechanism, and provide references for medical treatment.Methods Based on the improved split Hopkinson pressure bar (SHPB) experimental device, the adipose tissue dynamic compression experiment was conducted. The stress-strain curves of adipose tissues at different strain rates were obtained. Then the numerical model of SHPB was established, and the experimental process was simulated and analyzed. The numerical simulation for penetration process of 32 mm diameter rubber non-lethal projectile into the simulated target in human abdomen was carried out.Results Adipose tissues had a noticeable strain rate effect. The stress-strain curves at two high strain rates were approximately straight lines. The slope was similar, and the elastic modulus was 3.25 MPa, which was about 6 times of that under a quasi-static state. The simulation curves of fat SHPB were consistent with the experimental curves, which verified correctness of the constitutive model. In the process of non-lethal projectile penetrating human abdomen, an annular convex area similar to water wave appeared on skin surface, and the fat layer absorbed about 67% of the impact kinetic energy.Conclusions The experimental data of adipose tissues are very accurate. Numerical simulation can reproduce the penetration process well, and provide references for studying the damaging effect of non-lethal weapons on human body.

Numerical Analysis on Degradation of Cartilage Scaffold under Perfusion Loading / 医用生物力学

Objective To study the effect of irrigation mechanical stimulation on scaffold degradation by numerical simulation, so as to predict its degradation degree. MethodsBased on perfusion experimental data, the fluid-solid coupling model was established by Comsol. The finite element model of scaffold was established by ABAQUS. Based on the models, the degradation performance of scaffold was simulated and predicted. Results The fluid-solid coupling simulation showed that the initial pressure at the speed of 15.79 mL/min was two-fold of that at 7.89 mL/min. Along the thickness of scaffold from the surface to the bottom, the pressures between the two velocities were decreased and gradually close to each other. The degradation of scaffold structure could be simulated dynamically by combining the degradation constitutive model with the finite element model. The obtained degradation data were consistent with the experimental data, and the residual molecular weight reached 0.643 on the 56th day. Compared with the experimental data, the simulation accuracy was higher than 98%. Conclusions The larger the perfusion velocity is, the greater the pressure on scaffold will be. Under the same perfusion velocity, the maximum force occurs on the surface of scaffold. The degradation pattern of scaffold can be predicted by applying the degradation constitutive model and the finite element model.

The Effect of Torsion of Blood Vessel after Stent Implantation on Mechanical State of Stent / 中国医疗器械杂志

OBJECTIVE@#In daily life, the movement of the neck will cause certain deformation of the blood vessel and the stent. This study explores the quantitative influence of the torsion deformation of the blood vessel on the mechanical properties of the stent.@*METHODS@#In the finite element simulation software Abaqus, the numerical simulation of the crimping and releasing process of the stent, the numerical simulation of the torsion process of the blood vessel with the stent, and the numerical simulation of the pressure loading process of the outer wall of the blood vessel were carried out.@*RESULTS@#After the stent was implanted, when a load was applied to the outer surface of the blood vessel wall, when the applied load did not change, as the torsion angle increased, the smallest cross-sectional area in the blood vessel decreased.@*CONCLUSIONS@#After the stent is placed, when the external load is fixed, the radial support capacity of the stent will decrease as the torsion angle increases.

Simulation and Analysis of Capture Characteristics of Circulating Tumor Cells Based on Unidirectional Fluid-Solid Interaction Method / 医用生物力学

Objective To study movement process of circulating tumor cells (CTCs) in the blood and mechanism of CTC capture by CellCollector, and reveal relationship between the detected CTC numbers and the actual CTC concentration in the body. Methods Based on Fluent and EDEM software, the unidirectional fluid-solid interaction method was applied to establish a two-phase flow model, including the hemodynamic model and the CTC transport model, and capture simulations under different CTC concentration conditions were conducted. Results The number of CTCs captured by CellCollector was significantly positively correlated with the CTC concentration in the body. When the CTC concentration was low, CTCs could only be captured in several time intervals, and the capture had a certain contingency; as the concentration increased, the uniformity of CTC capture over time became better, and the total number of captures also increased. Conclusions Through the fitting of simulation results, analytical quantitative relationship between the captured CTC number and the CTC concentration in the body is preliminarily given, which provides theoretical basis and mechanical explanation for the clinical use of CellCollector.

Numerical Simulation on Aerodynamic Drag Reduction Evaluation of Vortex Generators Designed for Sprint Garment / 医用生物力学

Objective To investigate the effect from circumferential distribution angle of forwards wedge vortex generators on aerodynamic drag reduction during flow around a cylinder, so as to provide theoretical evidences for low drag sprint garment design. Methods Forwards wedge vortex generators were reconstructed based on the NIKE’s AeroBalde. Given that the individual parts of an athlete body can be treated as multiple cylinders with varied dimensions and positions, 48 forwards wedge vortex generators were distributed as four columns on windward side of the cylinder, which were symmetrical with the YOZ plane. When the air flowed through the cylinder at the speed of 32 km/h, large eddy simulation was carried out on the computational domains which were properly meshed with polyhedral mesh to investigate the drag force, flow filed and pressure distributions. Results It was effective for drag reduction of the cylinder induced by airflow when two columns of forwards wedge vortex generators were circumferential distributed in the range of 55°-75°and the circumferential internal angle between two columns was in the range of 10° or 15°. The pressure distribution on leeward side of the cylinder was apparently changed after surface modification, which minimized the pressure drag dominant in aerodynamic drag. The drag reduction mechanism was that micro-vortices were generated downstream after flow through the forwards wedge vortex generators, which resulted in an early transition to critical flow with low drag force. Conclusions Effective aerodynamic drag reduction is achieved if forwards wedge vortex generators are properly distributed. The research findings can provide guidance for wind tunnel test and low drag sprint garment design.

Research Progress in Fatigue Properties of Esophageal Stent / 医用生物力学

Due to the effect of structural characteristics and service environment of esophageal stent, fatigue damage of esophageal stent is developed easily, which may lead to serious complications. At present, the researches on fatigue performance of esophageal stent involve load spectrum, stress-strain relationship, fatigue crack and fatigue life prediction, and there are three main research method: theoretical analysis, numerical simulation and experimental research. In this paper, various analysis methods and limitations for measuring fatigue performance of esophageal stent are elaborated and summarized in detail, and the future research of esophageal stent is prospected.

Numerical simulation study of fracture mechanics of the atherosclerotic plaque / 生物医学工程学杂志

Atherosclerotic plaque rupture is the main cause of many cardiovascular diseases, and biomechanical factors play an important role in the process of plaque rupture. In the study of plaque biomechanics, there are relatively few studies based on fatigue fracture failure theory, and most of them mainly focus on the whole fatigue propagation process from crack initiation to plaque rupture, while there are few studies on the influence of crack on plaque rupture at a certain time in the process of fatigue propagation. In this paper, a two-dimensional plaque model with crack was established. Based on the theory of fracture mechanics and combined with the finite element numerical simulation method, the stress intensity factor (SIF) and related influencing factors at the crack tip in the plaque were studied. The SIF was used to measure the influence of crack on plaque rupture. The results show that the existence of crack can lead to local stress concentration, which increases the risk of plaque rupture. The SIF at the crack tip in the plaque was positively correlated with blood pressure, but negatively correlated with fibrous cap thickness and lipid pool stiffness. The effect of the thickness and angle of lipid pool on the SIF at the crack tip in the plaque was less than 4%, which could be ignored. This study provides a theoretical basis for the risk assessment of plaque rupture with cracks.

Structural design and biomechanical numerical analysis of body-fitted stent in stenotic vessels / 生物医学工程学杂志

To solve the problem of stent malapposition of intravascular stents, explore the design method of intravascular body-fitted stent structure and to establish an objective apposition evaluation method, the support and apposition performance of body-fitted stent in the stenotic vessels with different degrees of calcified plaque were simulated and analyzed. The traditional tube-mesh-like stent model was constructed by using computational aided design tool SolidWorks, and based on this model, the body-fitted stent model was designed by means of projection algorithm. Abaqus was used to simulate the crimping-expansion-recoil process of the two stents in the stenotic vessel with incompletely calcified plaque and completely calcified plaque respectively. A comprehensive method for apposition evaluation was proposed considering three aspects such as separation distance, fraction of non-contact area and residual volume. Compared with the traditional stent, the separation distances of the body-fitted stent in the incompletely calcified plaque model and the completely calcified plaque model were decreased by 21.5% and 22.0% respectively, the fractions of non-contact areas were decreased by 11.3% and 11.1% respectively, and the residual volumes were decreased by 93.1% and 92.5% respectively. The body-fitted stent improved the apposition performance and was effective in both incompletely and completely calcified plaque models. The established apposition performance evaluation method of stent considered more geometric factors, and the results were more comprehensive and objective.

Numerical Analysis on Adaptability of Valve Leaflets after Single Valve Replacement in Children / 医用生物力学

Objective To explore the biomechanical mechanism of aortic insufficiency (AI) after single aortic valve replacement (SAVR) in children and propose the corresponding countermeasures. Methods The idealized aortic valve model and postoperative growth model were constructed. By changing the length of leaflet free edge, leaflet height as well as improving the design with a concave structure, the effects of different structure dimensions on movement synchronization and closing performance of the aortic valve after surgery were compared. Results The closure of the replacement leaflet lagged behind the autologous leaflet, which fitted 2 mm below free edge of the replacement leaflet. AI occurred 6 years after operation. Increasing leaflet height could not improve the postoperative effect and would increase the maximum stress of the leaflet. Increasing free edge length by 10% could improve the postoperative outcomes, while increasing free edge length by 15% would cause the leaflet to be too long, hence resulting in a poor fit of the aortic valve. Compared with the traditional structure, the concave structure was more beneficial for closing performance of the aortic valve, and it could effectively reduce the maximum stress by 20% with the best effect. Conclusions The leaflet movement will be out of synchronization after SAVR, the point of convergence will be shifted, and AI will appear 6 years after surgery. It is recommended to use a concave structure with free edge length increased by 10%, while increasing leaflet height is not recommended.

Numerical simulation of a self-propelled fish-like swimmer with rigid and flexible caudal fins

Aim: In this paper, numerical simulations were conducted to investigate the swimming performances, hydrodynamics performances and wake structures of a self-propelled swimmer with rigid and flexible caudal fins.Methodology: The kinematics model of the swimmer was constructed using thunniform swimming. Using computational fluid dynamics (CFD) method, the systematic study of swimmer with rigid and flexible caudal fins was carried out. Results: The results showed that the caudal fin flexibility is beneficial to the fast-start of fish but not conducive to the fast cruising of fish. The fish with rigid caudal fin has larger cruising velocity inquasi-steady swimming and smaller forward acceleration in fast-start stage. In addition, the caudal fin flexibility is also beneficial to the heading stability of fish’s self-propelled swimming. The pressure distribution on the fish surface indicates that most of the thrust is generated by the leading-edge region of the caudal fin. The visualization of wake structures showed the existence of the attached leading-edge vortex (LEV) in thunniform swimming. Interpretation: Based on the present simulations, the hydrodynamic performance of tuna during self-propelled swimming was analyzed in detail. Researchers can use these findings to design bionic robot fish with rigid and flexible tails.

Numerical study on the mechanical coupling of external vascular stent and vein graft in coronary artery bypass surgery / 生物医学工程学杂志

External support stent is a potential means for restricting the deformation and reducing wall stress of the vein graft, thereby improving the long-term patency of the graft in coronary artery bypass surgery. However, there still lacks a theoretical reference for choosing the size of stent based on the diameter of graft. Taking the VEST (venous external support) stent currently used in the clinical practice as the object of study, we constructed three models of VEST stents with different diameters and coupled them respectively to a model of the great saphenous vein graft, and numerically simulated the expansion-contraction process of the vein graft under the constraint of the stents to quantitatively evaluate the influence of stent size on the radial deformation and wall stress of the vein graft. The results showed that while the stent with a small diameter had a high restrictive effect in comparison with larger stents, it led to more severe concentration of wall stress and sharper changes in radial deformation along the axis of the graft, which may have adverse influence on the graft. In order to solve the aforementioned problems, we ameliorated the design of the stent by means of changing the cross-sectional shape of the thick and thin alloy wires from circle into rectangle and square, respectively, while keeping the cross-sectional areas of alloy wires and stent topology unchanged. Further numerical simulations demonstrated that the ameliorated stent evidently reduced the degrees of wall stress concentration and abrupt changes in radial deformation, which may help improve the biomechanical environment of the graft while maintaining the restrictive role of the stent.