Generation of geometry of closed human head and discretisation for finite element analysis

Medical &; Biological Engineering &; Computing -     

Effects of head size and morphology on dynamic responses to impact loading

Head responses subjected to impact loading are studied using the finite element method. The dynamic responses of the stress, strain, strain energy density and the intracranial pressure govern the intracranial tissues and skull material failures, and therefore, the traumatic injuries. The objectivity and consistency of the prevailing head traumatic injury criteria, i.e., the energy absorption, the gravity centre acceleration and the head injury criterion (HIC), are examined with regard to the head dynamic responses. In particular, the structural intensity (STI) (the vector representation of energy flow rate) is calculated and discussed. From the simulations, the STI, instead of the gravity centre acceleration, the HIC and the energy absorption criteria, is found to be consistent with the dynamic response quantities. The different local skull curvatures at impact have a marginal effect whereas the locations of the impact loadings have significant effects on the dynamics responses or the head injury. The STI also shows the failure patterns.     

颅脑有限元模型的研究进展及应用

有限元法(finite element method,FEM)是随着电子计算机的发展而迅速发展起来的一种数值分析方法,同时也是一种比较先进的生物力学研究方法。FEM早期应用于工程科学技术领域,近几年来,生物医学工程领域已经广泛应用FEM进行脑方面的研究。随着交通、运输业的发展,颅脑损伤发生的概率越来越高,严重威胁着人类的身体健康。通过建立颅脑有限元模型,可以很好地研究颅脑损伤的生物力学机制。总结颅脑有限元模型的建立、发展和应用,并对未来的研究方向进行展望。     

外旋载荷对骨盆作用机制的三维有限元分析

目的利用骨盆的三维有限元模型研究外旋应力对骨盆的作用机制。方法 1例健康成年男性志愿者进行PET-CT扫描,结果以DICOM格式输出,在PC机上进行三维重建,建立正常骨盆的有限元模型。对模型施加外旋载荷,经计算得到应力、应变及位移云图。结果水平向后加载500N于左侧髂前上棘,应力沿两条途径传导:一条是向内后方经同侧骶髂关节前部至骶骨上部,另一条是向前方经耻骨支、耻骨联合至对侧耻骨;且骨盆前环受力较大。应变以同侧骶髂关节前下方最大,前方的耻骨联合处应变也较大。位移以受力点同侧髂前上棘处最大,同侧髂骨、坐骨及耻骨支位移均较大。结论外旋载荷易造成耻骨支骨折、骶髂关节损伤,或骶骨压缩骨折。     

颅脑有限元模型演化规律及其生物力学研究进展

交通事故中头颈部损伤因其较高的致命性,已成为最严重的损伤类型。有限元模型在创伤性脑损伤生物力学机理研究中得到日益广泛应用。回顾头颈部有限元模型的生物力学研究历史和现状,并阐述车辆碰撞交通事故中人体颅脑典型交通伤演化规律和生物力学研究进展,探索头颈部损伤安全防护的方法,以期为车辆碰撞事故中人体颅脑损伤生物力学研究和相应的汽车安全防护装置研制提供理论依据。     

不同骨缺损类型牙种植体的三维有限元分析

目的研究动态加载下不同骨缺损类型对种植体-骨整合界面、天然骨与Bio-oss成骨结合界面应力分布的影响。方法应用ANSYS软件,建立第1磨牙缺失并伴有不同类型骨缺损(旁穿型、裂开型、环型、垂直型)的4种模型,并建立各模型对应的植骨块和种植体模型,以200 N垂直载荷及100 N斜向载荷分别模拟咀嚼周期中5个阶段的动态受力过程,分析各组织结合界面应力分布情况。结果 4类骨缺损模型在一个咀嚼周期中,从第2到第4阶段,种植体-骨整合界面应力增幅依次为81.6%、90.7%、106%、182%,Bio-oss成骨与天然骨结合界面应力增幅依次为26%、13%、6%、56%。结论 4类模型的植骨稳定性为:环型骨缺损裂开型骨缺损旁穿型骨缺损垂直型骨缺损,在临床上种植医师应根据其植骨部位甄别出植骨高风险患者,治疗时应为骨植入材料选择不同的固定方式,最终提高植骨稳定性;垂直载荷更有利于各组织结合界面的应力分布状况,在临床设计种植义齿上部结构时应尽量减小或避免斜向载荷。     

利用有限元研究非贯穿弹道冲击防弹衣后人体躯干的力学响应

目的通过建立人体躯干有限元计算模型,对弹头非贯穿性弹道冲击下人体躯干主要脏器的力学响应进行数值模拟。方法利用正常成年男性的CT扫描数据,应用医学图像重建软件Mimics和有限元前处理工具Hy-perMesh进行人体躯干有限元建模,在显式动力有限元分析软件LS-DYNA中对速度为360 m/s的9 mm手枪弹弹头撞击装配有软质防弹衣人体躯干的压力、加速度响应进行数值计算。结果建立了包括胸廓骨骼结构、脏器、纵膈和肌肉/皮肤的人体躯干有限元模型,通过数值计算获得了心脏、肺脏、肝脏、胃的压力响应以及胸骨的加速度响应,发现不同脏器之间或同一脏器的不同位置,离弹头撞击点位置的远近决定了压力峰值的大小和出现压力峰值的时间。结论装配有软质防弹衣的人体躯干有限元计算模型可作为非贯穿弹道冲击下人体力学响应的仿真分析工具,仿真结果可为防弹衣后钝性损伤机制和防护研究提供依据。     

Biomechanical responses due to discitis infection of a juvenile thoracolumbar spine using finite element modeling

Growth modulation changes occur in pediatric spines and lead to kyphotic deformity during discitis infection from mechanical forces. The present study was done to understand the consequences of discitis by simulating inflammatory puss at the T12/L1 disc space using a validated eight-year-old thoracolumbar spine finite element model. Changes in the biomechanical responses of the bone, disc and ligaments were determined under physiological compression and flexion loads in the intact and discitis models. During flexion, the angular-displacement increased by 3.33 times the intact spine and localized at the infected junction (IJ). The IJ became a virtual hinge. During compression loading, higher stresses occurred in the growth plate superior to the IJ. The components of the principal stresses in the growth plates at the T12/L1 junction indicated differential stresses. The strain increased by 143% during flexion loading in the posterior ligaments. The study indicates that the flexible pediatric spine increases the motion of the infected spine during physiological loadings. Understanding intrinsic responses around growth plates is important within the context of growth modulation in children. These results are clinically relevant as it might help surgeons to come up with better decisions while developing treatment protocols or performing surgeries.     

全腰椎有限元模态分析

目的 采用三维有限元方法研究人体腰椎的动力学特性。方法 基于CT扫描图像建立并验证全腰椎L1~5节段有限元模型,对全腰椎进行有限元模态分析。结果 提取腰椎的30阶自由模态,获得了腰椎在自由状态下的动态特性：腰椎共振频率分布集中;各阶模态最大振幅急剧变化,L5节段腰椎附近的振幅较大,是腰椎的薄弱环节。结论 腰椎的模态分析是进一步进行动力学分析的基础,确定腰椎的固有频率、振型和振幅等振动参数,对于腰椎的振动特性分析和人机工程设计优化等方面具有重要意义。     

建立人体头颈动力学有限元模型和验证

目的建立符合解剖结构的头颈三维动力学有限元模型,研究冲击力作用下头颈部动力学响应。方法采用中国成年男性志愿者颈部CT扫描图像,获取颈椎三维点云数据,通过有限元前处理软件ICEM-CFD和Hyper Mesh建立颈部有限元模型。模型包括椎骨、椎间盘、小关节、韧带和软骨等组织,结合已建立并验证的头部有限元模型,装配成具有详细解剖结构的人体头颈部有限元模型。结果模型参考公开发表的头颈部轴向冲击实验数据进行验证,其颈部变形、头部加速度、接触力曲线以及损伤部位与实验数据吻合较好。结论动力学三维有限元模型可用于汽车安全、运动学损伤等领域人体头颈部的动态响应和损伤机制研究。     

Biomechanical study of tarsometatarsal joint fusion using finite element analysis

Complications of surgeries in foot and ankle bring patients with severe sufferings. Sufficient understanding of the internal biomechanical information such as stress distribution, contact pressure, and deformation is critical to estimate the effectiveness of surgical treatments and avoid complications. Foot and ankle is an intricate and synergetic system, and localized intervention may alter the functions to the adjacent components. The aim of this study was to estimate biomechanical effects of the TMT joint fusion using comprehensive finite element (FE) analysis. A foot and ankle model consists of 28 bones, 72 ligaments, and plantar fascia with soft tissues embracing all the segments. Kinematic information and ground reaction force during gait were obtained from motion analysis. Three gait instants namely the first peak, second peak and mid-stance were simulated in a normal foot and a foot with TMT joint fusion. It was found that contact pressure on plantar foot increased by 0.42%, 19% and 37%, respectively after TMT fusion compared with normal foot walking. Navico-cuneiform and fifth meta-cuboid joints sustained 27% and 40% increase in contact pressure at second peak, implying potential risk of joint problems such as arthritis. Von Mises stress in the second metatarsal bone increased by 22% at midstance, making it susceptible to stress fracture. This study provides biomechanical information for understanding the possible consequences of TMT joint fusion.     

足踝部有限元分析的临床应用综述

有限元分析可以计算结构内部的应力与应变,用于研究足踝部的生物力学有独特的优势,对足踝部疾病的病因、病理及治疗的临床研究具有重要的意义。目前研究主要内容有肌腱与韧带生物力学功能的分析,足部疾病的骨性结构的生物力学分析,内固定稳定性分析,另一方面用于足部支具、足垫的设计与足底压力分析相结合进行足部病因与治疗的研究。     

Importance of partitioning membranes of the brain and the influence of the neck in head injury modelling

A head injury model consisting of the skull, the CSF, the brain and its partitioning membranes and the neck region is simulated by considering its near actual geometry. Three-dimensional finite-element analysis is carried out to investigate the influence of the partitioning membranes of the brain and the neck in head injury analysis through free-vibration analysis and transient analysis. In free-vibration analysis, the first five modal frequencies are calculated, and in transient analysis intracranial pressure and maximum shear stress in the brain are determined for a given occipital impact load.     

血管支架不定形碳膜脱层现象实验及有限元分析

目的研究不定形碳涂层的血管支架在握压-扩张过程中发生涂层脱层的现象,从材料选择和尺寸设计方面避免脱层的发生。方法通过化学气相沉积法在金属血管支架上沉积生成不定形碳膜,实验模拟该涂层血管支架的握压-扩张过程,并通过电子扫描显微镜观察涂层发生脱层的情况。采用有限元方法分析不定形碳膜在血管支架握压-扩张过程中发生脱层的受力机制及影响因素。结果有限元结果能够较好吻合实验现象。不定形碳膜厚度决定了支架各处脱层的难易程度,以及脱层的发生形式。不定形碳膜弹性模量越大,支架越容易发生脱层。此外,支架的弹性模量也会对支架脱层产生影响,且在不同位置处影响规律不同。结论在血管支架涂层时,需要仔细设计不定形碳膜厚度以及合理匹配不定形碳膜和支架的弹性模量以避免脱层的发生。     

白内障超声乳化手柄的设计及ANSYS有限元优化分析

目的 设计小体积、振幅放大系数大的超声乳化手柄.方法 介绍了压电换能器和超声变幅杆的机电振动特性,分别使用等效电路法和解析法,对压电换能器和超声变幅杆的尺寸进行设计,并设计出了四分之一波长压电换能器和四分之一波长超声变幅杆;最后,使用有限元分析软件ANSYS11.0,进行模态和谐响应分析,对手柄进行仿真验证和加负载针头后手柄尺寸进行优化.结果 手柄纵向振动频率和振速振幅放大系数都与理论设计非常接近,误差分别为1.4％、5.8％;在压电陶瓷片上加载300V正弦电压时,针头末端振幅可达125.5μm,能达到白内障乳化手术的需要.结论 本设计大大减小了手柄的体积,获得了较大的振幅放大系数,仿真结果充分验证了理论设计的正确性.     

基于三维重建技术及有限元分析的脊柱骨密度测量及其意义

目的探讨基于三维重建技术及有限元分析的测量骨密度的方法。方法以1具脊柱标本(C3～L5)进行高速CT薄层扫描,在Mimics中进行每个椎体的三维重建,在Ansys中进行体网格划分,在Mimics中赋予10、400种材料属性,输出至Ansys计算骨骼中每一种材料属性的体单元的体积,根据CT扫描的Hu值与骨密度的经验公式,计算标本质量及密度,对照组以电子天平测量(C3～L5)的质量。进行统计学处理。结果(1)对照组、10种及400种材料属性组C3～L5的密度值分别为0.62±0.09、0.5813±0.0806、0.5813±0.0805g/cm3;(2)单因素方差分析:对照组与赋予10、400种材料属性各试验组比较的P值均大于0.1,试验组组别之间P=0.997。结论(1)本试验方法可定量测量骨骼密度及其密质骨及松质骨密度值;(2)赋予骨骼10种材料属性即可达到测量要求;(3)本试验为骨密度与有限元分析的统一作初步准备。     

A new method to evaluate the elastic modulus of cortical bone by using a combined computed tomography and finite element approach

This study attempted to estimate the elastic modulus of cortical specimens directly from the computed tomography (CT) number (CT). Cubic specimens of fresh bovine femora were tested under compressive loading. The corresponding three-dimensional mesh models of these specimens were established with the aid of CT images. The elastic modulus of each element was determined using the following transfer formula: E=A×(CT)^B. The A and B were determined by matching the simulation results with the experimental force-displacement curves. An optimization approach was used to match the entire specimen sets between simulations and experiments. The results indicated that the elastic modulus of cortical bone can be effectively estimated using a power relationship (E=1.26×10⁻³×(CT)^1.93) directly from the CT number. This procedure eliminates the need to determine the bone density, and therefore reduces the computational time required to define mechanical properties in finite element methods.     

Combined finite element and multibody dynamics analysis of biting in a Uromastyx hardwickii lizard skull

Lizard skulls vary greatly in shape and construction, and radical changes in skull form during evolution have made this an intriguing subject of research. The mechanics of feeding have surely been affected by this change in skull form, but whether this is the driving force behind the change is the underlying question that we are aiming to address in a programme of research. Here we have implemented a combined finite element analysis (FEA) and multibody dynamics analysis (MDA) to assess skull biomechanics during biting. A skull of Uromastyx hardwickii was assessed in the present study, where loading data (such as muscle force, bite force and joint reaction) for a biting cycle were obtained from an MDA and applied to load a finite element model. Fifty load steps corresponding to bilateral biting towards the front, middle and back of the dentition were implemented. Our results show the importance of performing MDA as a preliminary step to FEA, and provide an insight into the variation of stress during biting. Our findings show that higher stress occurs in regions where cranial sutures are located in functioning skulls, and as such support the hypothesis that sutures may play a pivotal role in relieving stress and producing a more uniform pattern of stress distribution across the skull. Additionally, we demonstrate how varying bite point affects stress distributions and relate stress distributions to the evolution of metakinesis in the amniote skull.     

基于有限元的骨组织工程支架结构力学性能优化分析

目的 分析骨组织工程支架微孔参数对支架力学性能的影响,为支架微孔结构的优化设计提供参考依据。方法 利用ANYSY软件建立支架微孔结构有限元模型,计算最大等效应力、最大总变形与孔隙率的关系,并分析比较不同孔径、孔间距结构对支架最大等效应力、最大总变形、内部应变的影响。结果 x、y轴方向孔间距的影响规律一致,随着孔间距从0.6 mm增加到2.0 mm,最大等效应力从63.1 MPa减小到46.3 MPa,最大总变形从23.8 μm减小到21.8 μm,最佳应变比从80%增大到84%;但随着z轴方向孔间距的增大,最大等效应力从38.3 MPa增大到47.8 MPa,最大总变形从20.8 μm增大到22.8 μm,最佳应变比在82%~85%波动。x,y轴方向孔径从0.1 mm增加到1.0 mm时,最大等效应力从32.4 MPa增大到78.4 MPa,最大总变形从19.9 μm增大到38.2 μm,最佳应变比从90%减小到53%;z轴方向孔径的增大会引起支架的最大等效应力从58.8 MPa减小到37.9 MPa,而最大总变形从23.3 μm增大到25.9 μm,最佳应变比从82%增大到87%。结论 支架孔隙率和最佳应变比越大,最大等效应力、最大总变形越小,支架生物性能和力学性能越好。研究结果对支架的结构设计和优化具有参考价值。     

Biomechanical consequences of progressive marginal bone loss around oral implants: a finite element stress analysis

The purpose of this study was to explore the biomechanical effects of progressive marginal bone loss in the peri-implant bone. Finite element model of a Ø 4.1 × 10 mm Straumann dental implant and a solid abutment was constructed as predefined eight-layers around the implant neck. The implant-abutment complex was embedded in a cylindrical bone model to analyze bone biomechanics regardless of anatomical influences. Angular and circular progressive marginal bone loss was simulated by sequential removal of each layer, resulting crater-like defects and a total of ten finite element models for analysis. Each model was subjected to a vertical and oblique static load of 100 N in separate load cases. Principal stress minimum and maximum, displacement, and equivalent of elastic strain outcomes were compared. Under vertical loading, principal stresses minimum and maximum decreased remarkably as with the increase in bone resorption. Under oblique load simulations, decrease in principal stress maximum and minimum was evident. With progressive bone loss and under oblique load simulations, displacement and equivalent of elastic strain increased considerably in trabecular bone contacting the implant neck. The presence of cortical bone contacting a load-carrying implant, even in a bone defect, improves the biomechanical performance of implants in comparison with only trabecular bone support as a sequel of progressive marginal bone loss.