摘要
Objective To investigate the hemodynamic effects of enhanced external counterpulsation(EECP)on cerebral arteries with different stenoses.Methods Zero-dimensional/three-dimensional multiscale hemodynamic models of cerebral arteries with different stenoses were constructed.Numerical simulations of the EECP hemodynamics were performed under different counterpulsation modes to quantify several hemodynamic indicators of the cerebral arteries.Among them,the mean time-averaged wall shear stress(TAWSS)downstream of the stenosis was in the range of 4-7 Pa,a low percentage of TAWSS risk area,and high narrow branch flow were considered to inhibit the development of atherosclerosis and create a good hemodynamic environment.Results For cerebral arteries with 50%,60%,70%,and 80%stenosis,the hemodynamic environment was optimal in counterpulsation mode when the moment of cuff deflation was 0.5,0.6,0.7,and 0.7 s within the cardiac cycle.Conclusions For 50%stenotic cerebral arteries,the counterpulsation mode with a deflation moment of 0.5 s should be selected.For 60%stenotic cerebral arteries,the counterpulsation mode with a deflation moment of 0.6 s should be selected.For 70%or 80%stenotic cerebral arteries,the counterpulsation mode with a deflation moment of 0.7 s should be selected.As stenosis of the cerebral arteries increases,the pressure duration should be prolonged.This study provides a theoretical reference for the EECP treatment strategy for patients with ischemic stroke with different stenoses.
摘要
Objective To study the compressive mechanical properties and constitutive models of brain tissue at different strain rates.Methods Quasi-static and medium-velocity compression tests were carried out on the white and gray matter of pig brain tissue using an electronic universal testing machine,and stress-strain curves of pig brain tissue at different strain rates were obtained.The Ogden constitutive model was used to fit the test curve,the parameters of the constitutive model were determined,and the simulation was verified using finite element software.Results The brain tissue stress-strain curves showed nonlinear characteristics,with a strong strain rate correlation and sensitivity.When tissues were compressed to 0.6 strain,the stress of white and gray matter increased by 102%and 129%,respectively,at a strain rate of 5×10-4-5×10-2 s-1,and by 50.7%and 54.6%,respectively,at a strain rate of 1-1.5 s-1.At a strain rate of 1.5 s-1,the stress in the white and gray matter increased by 347%and 413%,respectively,compared with that at 5×10-4 s-1 strain rate.The R2 value of the Ogden model was greater than 0.99,and the error between the simulation and experimental results was within 15%,thereby verifying the validity of the model.Conclusions This study is helpful for the prediction of brain tissue deformation and provides an accurate scientific theoretical basis for the establishment of scientific and reasonable human simulation targets as well as the design and improvement of brain-protective equipment.
摘要
Objective To study the corrosion-fatigue properties of a novel low modulus Ti-3Zr-2Sn-3Mo-25Nb(TLM)titanium alloy subjected to simulated body fluid(SBF).Methods Ti-6Al-4V(TC4)alloy was used as the control group.The electrochemical corrosion polarization curves of the two titanium alloys were measured in SBF.The pre-corroded TC4 and TLM titanium alloy samples were subjected to rotational bending fatigue tests.The loading stress amplitude and fatigue fracture cycle relationship was established using the experimental data,and the stress life curves were drawn.Subsequently,the fracture mechanism was analyzed by analyzing the corrosion fatigue micro-fracture morphology of the sample,and fatigue analysis on the titanium alloy sample was then conducted combined with the finite element software.Results The self-corrosion potential of the TC4 titanium alloy under stress annealing was lower than that of the TLM titanium alloy after heat treatment.The TLM titanium alloy was most sensitive to changes in cyclic stress.A comparison between the simulation and experimental results showed that the TC4 titanium alloy under stress annealing had a higher fatigue strength and stronger resistance to crack propagation than the TLM titanium alloy did after heat treatment,whereas its corrosion resistance was the opposite.Compared to the specimens without pre-corrosion treatment,the brittleness of the TLM titanium alloy increased,and its fatigue performance decreased after pre-immersion in SBF.Conclusions Through comparative analysis,the reliability of the test results proved to be high,and the COMSOL finite element software could effectively predict the fatigue life of titanium alloy materials.
摘要
Objective The biomechanical model for the musculoskeletal system of a human knee joint was established using a numerical simulation method.The kinematic and dynamic information captured during jumping motion simulated by the human dynamic model was used as driven data of the knee biomechanical model,followed by further analysis of the stress field distribution characteristics of the meniscus under different thermal-force coupling knee brace conditions.Methods Based on computed tomography and magnetic resonance imaging of the subject,a realistic human knee model,including bone,articular cartilage,meniscus,ligaments and peripheral soft tissues of the knee joint,was constructed.Furthermore,two gaits,namely taking-off and landing-on,of jumping motion with an increased risk of meniscus injuries were selected according to mechanical features in full-cycle jumping motion.Subsequently,the stress field characteristics of the knee meniscus under four different thermal-force coupling knee braces were analyzed,the changes of the peak stress of the meniscus and its stress concentration area were discussed,and the protective efficacy and mechanical basis of meniscal injuries and wearing knee braces were explored.Results The anterior part of the medial knee meniscus was a vulnerable area under concentrated stress.Under the knee brace thermal-force coupling condition,the stress concentration area of the medial meniscus was transferred from its narrow and weak anterior part to its wide and thick middle part,and the peak stress was also significantly reduced.The peak stress on the medial meniscus and that on the lateral meniscus were similar,indicating that the two parts of the meniscus bore the external load evenly,and the meniscus stress concentration area decreased.Conclusions Thermal-force coupling knee braces have good protective effects against knee meniscus injury.The numerical simulation provides theoretical support and technical guidance for the design of multifunctional thermal knee braces.
摘要
An intensive breast array sensor was designed based on three-dimensional electrical impedance tomography in this work.Firstly,an electrical impedance sensor for detection of breast cancer was developed.The sensor adopted the integrated design of excitation electrode array and ground electrode to achieve structural simplification.It realized electric field densification through conical matrix and double-layer circumferentially arranged electrode array and improved the detection accuracy of target object through taper optimization.Secondly,the imaging system was designed,and the sensor was optimized by numerical simulation.The simulation results showed that halving the number of electrodes did not affect imaging accuracy of the sensor,but could improve the imaging speed.Finally,the performance of the sensor was verified by experiment.The signal-to-noise ratio and channel consistency of the system were at a good level.The sensor was used to reconstruct three-dimensional image of the experimental model with relative volume of the detection field of 0.4%.The image correlation coefficient of the single target imaging was above 0.6 and the position of the double target object could be clearly identified,and thus the visual detection of breast cancer was realized.
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BACKGROUND:With social progress,the incidence rate of knee osteoarthritis is getting higher and higher in the face of the rapidly developing aging problem in the social population,and the number of total knee replacement operations is gradually increasing. OBJECTIVE:To study the relationship between prosthesis size and stress shielding by improving the tibial prosthesis base. METHODS:A female patient with severe knee osteoarthritis was selected.Based on Mimics,through extracting the bone structure of the knee joint and simulating the total knee replacement surgery,osteotomy,positioning,and implantation operations were carried out to establish the geometric modeling of the total knee replacement prosthesis(including the femoral prosthesis,tibial bracket,and tibial pad),and improve the design of the tibial prosthesis base,analyze the effect of different tibial prosthesis bases on stress shielding of surrounding bone tissue. RESULTS AND CONCLUSION:(1)Compared with single-stem tibial intramedullary stem prosthesis,the design of four-post tibial intramedullary stem prosthesis created a certain degree of stress shielding around the short stem.However,compared with a thicker single long stem,this stress shielding effect was significantly reduced,and the load was evenly distributed among the four short stems,so there was no stress concentration at the bottom of the pile.(2)The design with a rectangular hole in the middle not only provided relatively good stability,but also helped to reduce stress shielding of cancellous bone to a certain extent,with a reduction rate of 77.5%.(3)Compared with a single-stem tibial intramedullary stem prosthesis,both the four-post tibial intramedullary stem prosthesis and the four-post tibial intramedullary stem prosthesis with a hole in the middle have good stability,which can reduce stress shielding to a certain extent without causing stress concentration,providing theoretical guidance for the design of the tibial intramedullary stem.
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Objective To propose two different types of information encoding methods for the information encoding mode of neuronal networks based on Hodgkin-Huxley(HH)model.Methods The biological neuronal networks with different topologies were built with numerical simulations using HH model and chemical synapses.The specificities of two information encoding methods,namely average frequency encoding and interspike interval encoding,under the stimulus of sinusoidal signals and random audio signals were investigated,and the information encoding mode of neuronal networks stimulated by different signals was also analyzed.Results The information encoding mode of the neuronal networks was correlated with the stimulus signal type.When being stimulated by a continuous periodic signal,the neuronal network would generate a discharge sequence with periodicity corresponding to the stimulus signal.When the stimulus signal was a random signal,the discharge rate of the neuronal network would change with the stimulus signal intensity,and the higher the stimulus signal intensity was,the higher the action potential discharge rate was.Under the same stimulus signal,the temporal structure of the neuronal network discharge sequence was affected by the topology of the neuronal network.Conclusion The information encoding mode of neuronal networks is correlated with the stimulus signal,and the temporal structure of the discharge sequence of neuronal networks with different topologies is different.Interspike interval encoding has higher accuracy and contains more information,and the combination with the average frequency encoding can effectively express the dynamic change of the information encoding mode of neuronal networks under the stimulus.
摘要
@#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.
摘要
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.
Subject(s)
Vaccines , Disease Transmission, Infectious , Hemorrhagic Fever, Ebola , Models, Theoretical , Quarantine摘要
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.
摘要
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.
Subject(s)
Humans , Computer Simulation , Finite Element Analysis , Stents , Stress, Mechanical摘要
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.
Subject(s)
Humans , Cardiovascular System , Diastole , Heart Failure , Heart Rate , Heart-Assist Devices , Hemodynamics , Models, Cardiovascular摘要
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.
摘要
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.
摘要
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.
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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.
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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.
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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.
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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.
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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.