颅脑减速碰撞中脑组织空化效应的模拟研究

目的:构建一种新的方法用于再现颅脑减速撞击过程中对冲部位的空化效应.方法:制作含微气泡的透明颅脑物理模型,并将其安放在竖式颅脑减速撞击移动平台上.在高强度灯光的照明环境中,将移动平台以40 cm的高度自由下落而撞击固定台面,同时采用高速摄像记录减速撞击的整个过程.之后用序列图片分析软件计算微气泡的体积与平均压力的变化,研究碰撞过程中脑组织的空化效应.结果:位于撞击对侧的微气泡在撞击过程中其体积明显增大,位于撞击侧的微气泡在撞击过程中其体积减小,位于中性点的微气泡在撞击过程中其体积增减不明显.结论:该实验结果表明颅脑对冲部位出现了负压,存在空化现象.清晰直观地再现了颅脑减速撞击过程中对冲部位的空化效应.有助于在一定程度上较好地认识颅脑减速撞击过程中脑组织内动态应力的分布特点,为阐明交通事故伤中较为常见的颅脑"对冲伤"的力学发生机制提供一定的方法和实验基础.同时该方法对于研究颅脑减速撞击损伤的致伤机理及其诊断和防护具有重要意义.     

一种用于动物肝脏减速撞击伤机制研究的装置及实验探讨

目的：构建一种减速撞击装置,对小动物肝脏减速撞击过程中的受力方式进行研究,以便对汽车交通事故中驾乘人员可能存在的肝脏损伤特点进行分析。方法：通过肝脏自身的粘性将其置放于一可移动撞击平台上．此外．无其它约束。之后,使肝脏随同移动平台从一定的高度自由下落并撞击一固定台面。通过对撞击前后的肝脏照片情况进行比对．可以明确肝脏的损伤方式进而确定肝脏的受力方式。结果：在肝脏的减速撞击过程中．在对冲部位出现了明显的撕裂伤,该部位的伤情也是整个肝脏最严重的伤情所在位置。此外,在肝脏的撞击部位未见明显的撕裂伤。提示,在肝脏的减速撞击过程中,其对冲部位受到了相对较大的拉伸应力的作用。讨论：一般而言,生物体软组织的抗拉伸致伤的性能较弱,而其抗压缩致伤的性能相对较好。因此,在肝脏的减速撞击过程中,其对冲部位在较大的拉伸应力的作用下易于损伤并且往往是最严重的损伤发生的部位。结论：该装置可以很方便地应用于肝脏减速撞击损伤机制的研究。在交通事故中,组织器官对冲部位潜在的撕裂伤产生的可能性往往是最大的,这部分组织需要得到更多更有效的保护。因此在后续的研究中,这种损伤的生物力学机制研究应是重点之一。     

颅脑对冲伤的监护进展

重型颅脑损伤是一种严重的创伤类型,发生率较高据统计我国城市中伤死病例的60%为颅脑损伤。Miller等报告颅脑对冲伤死亡率为35%左右〔1,2〕。国内外对颅枕部对冲伤的预防、急救、监护都很重视。国内对于脑损伤后的系列变化进行了探索,特别注重伤后的监护,从而大大提高了颅脑损伤的救治率,现就目前颅脑对冲伤的监护体系作一综述。1　颅脑对冲伤的发病机制颅枕对冲损伤大多是在受撞击处的对侧,如枕部着地者的额叶、颞叶的前方脑组织可发生脑挫裂伤(对冲伤所致),而枕部脑组织常可无损伤或损伤轻(击伤所致)。对冲伤的形成,是由于颅骨和脑组织在…     

活性猪眼角膜的各向异性生物力学行为研究

以猪眼角膜为研究对象,应用实验分析和各向异性弹性理论,探讨动物角膜在双向载荷作用下的生物力学行为.在Zwick-Z010型小吨位双向电子万能试验机上,利用所开发的平口微型双轴夹具,分别对片状角膜进行单、双轴拉伸和循环加载实验,确定材料的弹性常数和强度、刚度等特性.研究表明,材料具有典型的各项异性生物力学行为,在角膜的长轴和短轴方向呈现出不同的应力和变形特征.沿短轴方向角膜具有更高的黏弹性和黏塑性,其延展率也要大于长轴方向,而沿长轴方向则有更高的弹性模量和拉伸极限强度,材料的破坏为多种变形相互作用所致.     

空间调谐神经元的动态极化矢量

研究耳石神经元的动态特性过去一直被认为很困难,这是由于不同的细胞对特殊刺激方向有不同的响应灵敏性,同时也缺少一个基本数学模型来解释说明这些响应特性。本文描述了一种方法用于估计,类似耳石神经元经空间调谐具有不同的刺激方向,这种神经元的空间和时间响应特性。在每一个刺激频率,沿着三个线性独立轴的刺激诱发的神经响应能形成一个响应椭球。椭球的半长轴将精确测定神经元最大灵敏方向(即极化矢量),同时半短轴将说明垂直方向的灵敏性,这种非零半短轴方法能够预测同时实验观察到相位响应     

与影像相关的标本肝叶垂直斜剖面测量指标优化

目的研究肝叶垂直斜剖面（OSS）形态学特征,筛选优化测量指标,为评估肝脏疾患早期影像形态学变化提供研究基础。方法通过对37例正常肝标本OSS观察长、短轴指标的测量,获取成人的标准值;研究各指标之间的比例关系;通过检测变异程度,筛选稳定性好的观察指标。结果剖面长轴RMa、QMa、Li Ma、Lu Ma长度分别为（152.3±19.30）mm、（126.7±15.17）mm、（104.60±13.99）mm、（87.40±13.26）mm。剖面短轴RMi、QMi、Li Mi、Lu Mi长度分别为（88.4±9.11）mm、（67.54±7.52）mm、（58.70±6.29）mm、（46.4±5.66）mm。肝叶比例以RMa为基数,各剖面长轴之比Rrmaqma、Rrmaluma、Rrmalima、分别为1.2±.07、1.8±0.22、1.5±0.17,左肝上、下长轴之比为0.8±0.06。肝叶OSS诸指标中,长、短轴长度以及肝叶比例尤其叶内比例变异系数（coefficient of variation,CV）值较小,为6%~12%,各剖面轴之间CV差异无统计学意义（P〉0.05）。右肝下极和网膜结节高度CV亦较小。结论肝叶OSS长、短轴比例关系尤其肝叶内比例关系具有良好的稳定性,可以作为肝脏影像形态学首选早期观察指标;Qma膈面顶点、RMa（代表右肝下极）、Li Ma和Lu Ma脏面顶点（代表网膜结节）稳定性亦好,亦可以作为观察指标。     

小腿骨间膜结构及其上端裂孔的临床解剖

目的 :研究小腿骨间膜上端裂孔的形态结构,为临床深入了解小腿骨间膜的功能,重建和避免胫前血管损伤提供形态学依据。方法 :常规福尔马林固定小腿骨间膜标本40侧,观测胫、腓骨长度;骨间膜结构;骨间膜上端裂孔的形态;裂孔长轴腓侧近端至外踝的距离,计算骨间膜上端裂孔长轴腓侧近端至外踝距离与腓骨长的相关性。结果 :骨间膜由膜性部和腱性部2部分组成。腱性部是一条斜型粗纤维束,位于骨间膜下1/2处,由走行一致的多条细小纤维构成,厚(0. 32±0.12)cm,长(11.1±0.21)cm,与腓骨成角(20. 60°±1.00°)。上端裂孔成椭圆形,上端裂孔长轴长(2.71±1.35)cm、上端裂孔短轴长(1.91±0.21)cm、长轴近端腓侧至外踝最远处距离为(31.21±2.35)cm。胫骨长(34.21±2.36)cm、腓骨长(34.3±2.12)cm。骨间膜上端裂孔长轴腓侧近端至外踝距离与腓骨长正相关。结论:骨间膜对维持胫、腓骨轴向稳定,应力传递和防止小腿损伤后胫、腓骨移位具有重要作用。骨间膜上端裂孔的位置可由腓骨长推算而出。     

实时剪切波弹性成像量化评估健康人正中神经弹性特征的信度

背景：实时剪切波弹性成像技术可无创测量组织弹性,目前较多地应用于甲状腺、乳腺等软组织疾病,而应用于周围神经及其病变的研究相对少见。目的：使用实时剪切波弹性成像技术量化评估健康人正中神经的重测信度及测试者间信度,探究同一测量位点正中神经长轴与短轴弹性模量的相关性。方法：随机招募20名健康受试者参与该试验,10名男性,10名女性。在信度试验中,测试者A和B分别使用实时剪切波弹性成像技术测量受试者利手侧、非利手侧正中神经长轴放松状态时的弹性模量;5 d后,测试者A以相同的测量方法对受试者正中神经弹性进行量化评估。此外,使用实时剪切波弹性成像技术在受试者腕横纹处测量正中神经长轴以及短轴的弹性模量完成相关试验。结果与结论：(1)在信度试验中,利手侧正中神经的测试者间信度表现为优秀：其组内相关系数为0.98,重测信度优秀(组内相关系数=0.96);非利手侧,测试者间信度和重测信度均表现为好(组内相关系数=0.78,0.86);(2)正中神经长轴与其短轴弹性模量之间无相关性(r=0.039,P=0.87);(3)提示剪切波弹性成像技术能准确量化评估出健康人利手侧以及非利手侧正中神经弹性模量特征,且可...     

肝叶长轴垂直斜面形态结构及潜在临床影像诊断价值

目的:观察标本肝叶长轴垂直斜断面及肝表面形态结构,探讨肝叶长轴垂直斜断面潜在的临床影像诊断意义。方法:对37例成人尸肝经左叶上、下段,方叶和右叶长轴、且垂直于横轴面之斜断面以及肝表面标志进行命名,对其形态进行观察,并研究其相应长轴和短轴与肝表面结构的联系。结果:肝表面标志形态:网膜结节以半椭球型为主,占86·5%;方叶后区以平坦型为主,占83·8%;右肝下极丘型,占91·9%;肝嵴线型、平坦型分别占81·1%和11%。各叶斜断面形态与特点:均由前后两个近似三角形组成,各断面前三角形顶点之连线与肝膈面最膨隆带区重叠;肝左叶上、下段长轴斜断面后三角形顶点均100%与网膜结节重叠;方叶长轴斜断面后三角形顶点有16·2%不落在方叶后区上;右叶长轴斜断面后三角形顶点为丘型右肝下极占91·9%,顶点在右肝嵴线上占8%,两者重叠率均为100%。结论:肝各叶斜断面形态均由前后两个近似三角形组成,其两个三角形顶点分别落在肝腹侧和脏侧最隆起肝表面标志结构上,诸断面能够良好的反映上述肝表面标志形态大小的变化。     

俯卧位腰椎交叉按压微调法(横突)作用力测量与初步分析

目的测量俯卧位腰椎交叉按压微调法(横突)的作用力和作用点,探讨其治疗腰椎疾病的力学机制。方法采用离体实验的方法采集手法作用力和作用点数据,其中作用力由2台FZ-I型推拿手法测定仪和2个三分力测力指套测得,作用点由普通数码相机测得。在此基础上,计算各主要作用力形成的力矩,从生物力学的角度分析各作用力的作用效果。结果得到了手法作用力-时间关系图和手法作用点示意图,左右手垂直作用力产生的力矩同轴,且方向相反,左右手水平作用力产生的力矩方向相同,但异轴。结论俯卧位腰椎交叉按压微调法(横突)的作用力主要具备两种作用效果,一方面,通过"拉伸"使相邻两椎骨产生松动,减少椎骨间的摩擦,有利于整复;另一方面,通过"扭转"使相邻两椎骨整复,以达到治疗疾病的目的。     

基于有限元法的人类头部损伤生物力学的模拟分析

根据正常头部螺旋CT扫描影像，通过对CT扫描影像的图像处理，利用计算机辅助工程技术，采用单元网格划分和三维重构技术，开发、建立了三维的人类头部有限元计算模型。应用本模型模拟颅脑在直接碰撞中的生物力学问题。计算模型比较真实地反映了头颅实际碰撞实验中的物理反应，比较忠实地再现了某些实验的结果，如头部撞击合力和脑压力/强等。同时，脑压力，强的分布再次证实了经典的撞击压-对撞压产生理论。本研究的计算模型可为进一步的头部损伤生物力学研究提供一种新的工具。     

An analysis of contact stiffness between a finger and an object when wearing an air-cushioned glove: the effects of the air pressure

Air-cushioned gloves have the advantages of lighter weight, lower cost, and unique mechanical performance, compared to gloves made of conventional engineering materials. The goal of this study is to analyze the contact interaction between fingers and object when wearing an air-cushioned glove. The contact interactions between the the fingertip and air bubbles, which is considered as a cell of a typical air-cushioned glove, has been analyzed theoretically. Two-dimensional finite element models were developed for the analysis. The fingertip model was assumed to be composed of skin layers, subcutaneous tissue, bone, and nail. The air bubbles were modeled as air sealed in the container of nonelastic membrane. We simulated two common scenarios: a fingertip in contact with one single air bubble and with two air cushion bubbles simultaneously. Our simulation results indicated that the internal air pressure can modulate the fingertip-object contact characteristics. The contact stiffness reaches a minimum when the initial air pressure is equal to 1.3 and 1.05 times of the atmosphere pressure for the single air bubble and the double air bubble contact, respectively. Furthermore, the simulation results indicate that the double air bubble contact will result in smaller volumetric tissue strain than the single air bubble contact for the same force.     

In vivo bubble nucleation probability in sheep brain tissue

Gas nuclei exist naturally in living bodies. Their activation initiates cavitation activity, and is possible using short ultrasonic excitations of high amplitude. However, little is known about the nuclei population in vivo, and therefore about the rarefaction pressure required to form bubbles in tissue. A novel method dedicated to in vivo investigations was used here that combines passive and active cavitation detection with a multi-element linear ultrasound probe (4-7 MHz). Experiments were performed in vivo on the brain of trepanated sheep. Bubble nucleation was induced using a focused single-element transducer (central frequency 660 kHz, f-number = 1) driven by a high power (up to 5 kW) electric burst of two cycles. Successive passive recording and ultrafast active imaging were shown to allow detection of a single nucleation event in brain tissue in vivo. Experiments carried out on eight sheep allowed statistical studies of the bubble nucleation process. The nucleation probability was evaluated as a function of the peak negative pressure. No nucleation event could be detected with a peak negative pressure weaker than -12.7 MPa, i.e. one order of magnitude higher than the recommendations based on the mechanical index. Below this threshold, bubble nucleation in vivo in brain tissues is a random phenomenon.     

Effect of isobaric breathing gas shifts from air to heliox mixtures on resolution of air bubbles in lipid and aqueous tissues of recompressed rats

Deep tissue isobaric counterdiffusion that may cause unwanted bubble formation or transient bubble growth has been referred to in theoretical models and demonstrated by intravascular gas formation in animals, when changing inert breathing gas from nitrogen to helium after hyperbaric air breathing. We visually followed the in vivo resolution of extravascular air bubbles injected at 101 kPa into nitrogen supersaturated rat tissues: adipose, spinal white matter, skeletal muscle or tail tendon. Bubbles were observed during isobaric breathing-gas shifts from air to normoxic (80:20) heliox mixture while at 285 kPa or following immediate recompression to either 285 or 405 kPa, breathing 80:20 and 50:50 heliox mixtures. During the isobaric shifts, some bubbles in adipose tissue grew marginally for 10–30 min, subsequently they shrank and disappeared at a rate similar to or faster than during air breathing. No such bubble growth was observed in spinal white matter, skeletal muscle or tendon. In spinal white matter, an immediate breathing gas shift after the hyperbaric air exposure from air to both (80:20) and (50:50) heliox, coincident with recompression to either 285 or 405 kPa, caused consistent shrinkage of all air bubbles, until they disappeared from view. Deep tissue isobaric counterdiffusion may cause some air bubbles to grow transiently in adipose tissue. The effect is marginal and of no clinical consequence. Bubble disappearance rate is faster with heliox breathing mixtures as compared to air. We see no reason for reservations in the use of heliox breathing during treatment of air-diving-induced decompression sickness.     

Transversely isotropic properties of porcine liver tissue: experiments and constitutive modelling

Knowledge of the biomechanical properties of soft tissue, such as liver, is important in modelling computer aided surgical procedures. Liver tissue does not bear mechanical loads, and, in numerical simulation research, is typically assumed to be isotropic. Nevertheless, a typical biological soft tissue is anisotropic. In vitro uniaxial tension and compression experiments were conducted on porcine cylindrical and cubical liver tissue samples respectively assuming a simplistic architecture of liver tissue with its constituent lobule and connective tissues components. With the primary axis perpendicular to the cross sectional surface of samples, the tissue is stiffer with tensile or compressive force in the axial direction compared to that of the transverse direction. At 20% strain, about twice as much force is required to elongate a longitudinal tissue sample than that of a transverse sample. Results of the study suggest that liver tissue is transversely isotropic. A combined strain energy based constitutive equation for transversely isotropic material is proposed. The improved capability of this equation to model the experimental data compared to its previously disclosed isotropic version suggests that the assumption on the fourth invariant in the constitutive equation is probably correct and that anisotropy properties of liver tissue should be considered in surgical simulation.     

Prevention of air bubble formation in a microfluidic perfusion cell culture system using a microscale bubble trap

Formation of air bubbles is a serious obstacle to a successful operation of a long-term microfluidic systems using cell culture. We developed a microscale bubble trap that can be integrated with a microfluidic device to prevent air bubbles from entering the device. It consists of two PDMS (polydimethyldisiloxane) layers, a top layer providing barriers for blocking bubbles and a bottom layer providing alternative fluidic paths. Rather than relying solely on the buoyancy of air bubbles, bubbles are physically trapped and prevented from entering a microfluidic device. Two different modes of a bubble trap were fabricated, an independent module that is connected to the main microfluidic system by tubes, and a bubble trap integrated with a main system. The bubble trap was tested for the efficiency of bubble capture, and for potential effects a bubble trap may have on fluid flow pattern. The bubble trap was able to efficiently trap air bubbles of up to 10 μl volume, and the presence of captured air bubbles did not cause alterations in the flow pattern. The performance of the bubble trap in a long-term cell culture with medium recirculation was examined by culturing a hepatoma cell line in a microfluidic cell culture device. This bubble trap can be useful for enhancing the consistency of microfluidic perfusion cell culture operation.     

Combining mechanical foaming and thermally induced phase separation to generate chitosan scaffolds for soft tissue engineering

In this paper, a novel foaming methodology consisting of turbulent mixing and thermally induced phase separation (TIPS) was used to generate scaffolds for tissue engineering. Air bubbles were mechanically introduced into a chitosan solution which forms the continuous polymer/liquid phase in the foam created. The air bubbles entrained in the foam act as a template for the macroporous architecture of the final scaffolds. Wet foams were crosslinked via glutaraldehyde and frozen at ?20 °C to induce TIPS in order to limit film drainage, bubble coalescence and Ostwald ripening. The effects of production parameters, including mixing speed, surfactant concentration and chitosan concentration, on foaming are explored. Using this method, hydrogel scaffolds were successfully produced with up to 80% porosity, average pore sizes of 120 μm and readily tuneable compressive modulus in the range of 2.6 to 25 kPa relevant to soft tissue engineering applications. These scaffolds supported 3T3 fibroblast cell proliferation and penetration and therefore show significant potential for application in soft tissue engineering.     

The morphology and mechanical properties of endomysium in series-fibred muscles: variations with muscle length

Summary In the series-fibred muscle architecture commonly found in large muscles of mammals and birds, the intrafasciculary-terminating muscle fibres have no direct tendinous attachments. Contractile force produced in these fibres must be transmitted between adjacent muscle fibres via the endomysial connective tissue which separates them. The endomysium is thus an essential mechanical component in such muscles. Studies of motor end-plate banding patterns and the frequent occurrence of tapering ends of fibres within the fascicles of the bovine sternomandibularis muscle show it to be a series-fibred muscle. Sodium hydroxide digestion of fixed samples of this muscle to remove the myofibrillar apparatus revealed the endomysium to be a disordered planar network of mainly curvilinear collagen fibrils.The orientation distribution of the collagen fibrils in the endomysial network was measured by image analysis of scanning electron micrographs. Analysis of endomysial preparations from muscle fixed at sarcomere lengths between 1–4 m showed that the orientation distribution of collagen fibrils is quantitatively related to muscle length. At rest sarcomere length the collagen fibril network is not completely random, but has a slight circumferential bias. The orientation distribution shows a progressive shift towards the circumferential direction at short sarcomere lengths and towards the longitudinal direction at long sarcomere lengths. The relationship between the number-weighted mean collagen orientation and sarcomere length was compared to two geometric models of network behaviour, the isoareal and constant shape models. both fitted the data reasonably, although the constant shape model described the rate of change of mean orientation more closely.From fibrous composites theory, the reinforcement efficiency factor, was calculated from the measured collagen fibril orientation distributions. These calculations predict a non-linearly increasing longitudinal tensile modulus for the endomysium with increasing sarcomere length, in agreement with its known non-linear properties, but confirm that the tensile properties of the endomysium are unsuitable for transmission of tensile force from muscle fibres contracting near rest length. This reinforces a previous interpretation that contractile force is transmitted between neighbouring muscle fibres by trans-laminar shear through the endomysium rather than by in-plane tension.