人密质骨的撞击实验研究

本文用分离式Hopkinson杆（SHBM）（应变率为7001/s)对人的密度骨进行撞击实验研究,得出了应力-时间、应变-时间、应变率-时间及应力-应变等曲线。用一维波传播理论分析实验数据。结果表明即使在高应变率下,人的密质骨也具有非线性粘弹性材料的特性,据此可得人密质骨的冲击特性可用三参数粘弹性力学模型描述,同时得出了高应变率下,人的密质骨也具有非线性粘弹性材料的特性。据此可得人密质骨的冲击特性可用三参数粘弹性力学模型描述,同时得出院高应变率下人密度骨的极限应力和残余应变值。     

人类白细胞的被动变形分析

本文利用实验和理论方法对人类白细胞的被动粘弹性行为做了研究。实验中,观察了置于EDTA溶液中的单个嗜中性白细胞部分吸入小的微吸管和从一个较大的微吸管中完全吸出后的变形情况。过去的理论研究把白细胞当作一个均质的实心球,而本文的模型则把自细胞看作一个内有Haxwell流体的皮质壳,其中的流体用以描述细胞质的平均特性,而该皮质壳则表征靠近表面的交叉肌动朊层,并假设此层受到预加的张应力。在由大微吸管中吸出后,这个张力使变形的细胞恢复成球形。在小应变     

人体椎间盘粘弹性特性的研究

为了确定人体椎间盘的粘弹性常数,作者设计了一个实验装置,对六个个体的三十九个椎间盘分别进行了单轴向压缩蠕变,复合载荷下的轴向压缩蠕变等大量实验。结果发现:三参数模型能很好地模拟椎间盘的轴向压缩蠕变,而用二参数模型去模拟,初始误差太大。作者提议在救生的动力学模型中,应用三参数模型来模拟推间盘的力学行为、文中求出了人体椎间盘的二参数模型和三参数模型的粘弹性常数。本文实验结果为脊柱的动力学模型提供了基础数据,还能为人工椎间盘的研制提供理论和设计依据。     

在体软组织非线性粘弹性的自适应准线性粘弹性模型研究

在手术仿真、手术规划、医学诊断等众多医学应用中,人体软组织力学特性建模都是一个关键问题。为了开发手术仿真中人体软组织大变形生物力学模型,本文介绍了自适应准线性粘弹性(AQLV)模型,对人体前臂软组织进行了印压试验,采用增量斜坡保持试验得到模型参数,通过增量斜坡保持试验、大应变斜坡保持试验和大应变正弦循环加载试验来检验该模型的预测能力。本文研究结果表明,AQLV模型能够较好地预测这三种加载工况下的试验数据。因此,本研究的结论认为,该AQLV模型对在体软组织在大应变时的非线性粘弹性的描述具有一定的实用性和可参照性,有望作为手术仿真或医学诊断中软组织模型的选择之一。     

生物组织粘弹性动力学分析的有限元新方法

应用线性粘弹性模型和电网模型间的两个重要结论,以及滤波方法,推导得出一种适用于生物组织粘弹性动力学分析的有限元新方法。粘弹性材料的复杂性可简单地视为各向同性,亦可将其逐步趋地复杂而直臻极端各向异性,描述生物组织力学特性的线性粘弹性模型可以是两种不同的元件和三种不同的基本模型的任意组合,多方法,多角度地证实本文推导得出了一般的系统的和高精度的快速有限元分析法,该分析法可用于分析以线性粘弹性为模型的生物组织和工程材料的动力学响应。     

长春花碱和细胞松驰素D对肝癌细胞粘弹性的影响

用微管吸吮技术测定了正常肝细胞和肝实质细胞癌细胞的粘弹性，以三参数标准线性固体模型拟实验结果，进一步研究了两种细胞骨架干扰剂处理后肝细胞和肝癌细胞粘弹性系数的变化。     

几种典型心脑血管疾病血液滞后环及其数学表征

本文针对几种典型心脑血管疾病的血液滞后环同正常人的进行了对比。并采用新型5参数时变性本构方程确切描述了这些滞后环曲线,模型计算值与实验曲线吻合良好。定量揭示其中包含的粘弹性和触变性,获得了各种典型心脑血管疾病的血液粘弹性指标和触变性指标。同正常人相比,心脑血管疾病的血液粘弹性指标较高,而触变性指标较差,结果合理。从而为利用动态血流变特性进行心脑血管疾病临床辅助诊断提供了一个新方法。     

急性脑梗塞患者白细胞流变性观察

本文用核孔膜滤过法,对40例急性脑梗塞病人和30例健康查体者的白细胞流变学及其他有关指标进行了测定,结果显示病人组较对照组白细胞变形能力下降极明显,提示白细胞流变性异常是脑梗塞的重要危险因素,而其他流变学指标也不同程度的参与或影响脑梗塞的发生发展。本文白细胞变形能力除用滤过堵塞的粒子浓度和变形指数表示外,尚用红白细胞变形指数—红细胞变形指数的差值表示,这样可排除红细胞的干扰,真实反映白细胞变形能力。     

正弦波刺激对人肺腺癌细胞粘弹性的影响

目的通过FX-4000柔性基底加载系统研究正弦波拉伸培养对体外人肺腺癌A549细胞粘弹性的影响。方法采用微管吸吮技术考察A549细胞的粘弹性特性,将不同拉伸幅度培养下的A549细胞与对照组细胞粘弹性进行对照,选择三参数标准线性固体模型拟合实验结果并用三个粘弹性系数比较各组A549细胞的力学性质。结果在胶原蛋白基底膜上,正弦波、频率0.5Hz、加载4h时,与对照组比较,15%的拉伸应变组A549细胞的粘弹性系数k_1、k_2和μ值均有所降低;与1.5%的拉伸应变组A549细胞的粘弹性系数比较无明显差异。结论15%的拉伸应变刺激培养后A549细胞更容易变形,细胞刚性有所减小。癌细胞粘弹性的改变可能影响到浸润和转移特性以及癌细胞与其微观力学环境的相互作用。     

用复合液滴模型研究黏附于血管表面白细胞的变形性

用复合液滴模拟黏附于血管表面的白细胞,通过引入"变形指数",研究稳定剪切流动下白细胞及其细胞核发生的变形.结果表明,白细胞的变形随着初始接触角、外界流场雷诺数的增大而增大.虽然细胞核也能随白细胞的变形而变形,但其变形指数总是小于白细胞.因此,具有高黏性的细胞核在白细胞的变形过程中可能起到特殊作用.     

慢性肺心病急性发作期患者红细胞膜黏弹特性研究

采用微管吸吮技术研究了正常健康人与慢性肺源性心脏病急性发作期患者红细胞在吸进微管的变形过程,采用二维V o igt模型拟合实验结果,定量地比较了正常人与肺心病患者红细胞膜的黏弹特性,结果表明:肺心病患者红细胞膜的弹性模量((6.970±1.050)×1-0 3dyn/cm)、黏性系数((0.936±0.475)×1-0 4dyn.s/cm)分别显著高于正常健康人的弹性模量((5.203±1.051)×1-0 3dyn/cm)、黏性系数((0.620±0.053)×10-4dyn.s/cm)。红细胞膜弹性模量与黏性系数增加、膜刚性增加,黏滞性增大。这可能是引起红细胞变形性降低乃致慢性肺源性心脏病急性发作期高黏滞血症的重要亚细胞机制。     

Large Deformation Finite Element Analysis of Micropipette Aspiration to Determine the Mechanical Properties of the Chondrocyte

Chondrocytes, the cells in articular cartilage, exhibit solid-like viscoelastic behavior in response to mechanical stress. In modeling the creep response of these cells during micropipette aspiration, previous studies have attributed the viscoelastic behavior of chondrocytes to either intrinsic viscoelasticity of the cytoplasm or to biphasic effects arising from fluid–solid interactions within the cell. However, the mechanisms responsible for the viscoelastic behavior of chondrocytes are not fully understood and may involve one or both of these phenomena. In this study, the micropipette aspiration experiment was modeled using a large strain finite element simulation that incorporated contact boundary conditions. The cell was modeled using finite strain incompressible and compressible elastic models, a two-mode compressible viscoelastic model, or a biphasic elastic or viscoelastic model. Comparison of the model to the experimentally measured response of chondrocytes to a step increase in aspiration pressure showed that a two-mode compressible viscoelastic formulation accurately captured the creep response of chondrocytes during micropipette aspiration. Similarly, a biphasic two-mode viscoelastic analysis could predict all aspects of the cells creep response to a step aspiration. In contrast, a biphasic elastic formulation was not capable of predicting the complete creep response, suggesting that the creep response of the chondrocytes under micropipette aspiration is predominantly due to intrinsic viscoelastic phenomena and is not due to the biphasic behavior.     

A low drift micropipette holder

A novel micropipette holder has been designed to overcome the problem of drift enountered when experimenting on small preparations using patchclamp techniques. In order to increase the stiffness and thermal stability of the system, the holder is designed such that the micropipette is clamped to a rigid quartz rod, and isolated from stresses arising in the connectors. The pressure line, made from stiff tubing, and electrical leads are firmly attached to the table and micromanipulator. This design was able to hold the micropipette tip stable to with 100 nm for more than 1 h, even with changes of 26.7 kPa (200 mmHg) in the pressure line.     

A micromechanical technique for monitoring cell-substrate adhesiveness: measurements of the strength of red blood cell adhesion to glass and polymer test surfaces

We report a novel method for rapid comparison of the relative strength of adhesion of cells to different solid surfaces. A vertically oscillating micropipette is brought above an individual cell in such a manner that it makes contact with the cell at the lower limit of its travel. The pressure within the micropipette is gradually reduced until the cell attaches to the micropipette by suction and is lifted from the solid surface. The reduction in pressure required to detach a cell depends on the specific cell/substrate combination and serves as a relative measure of the strength of cell adhesion. A particular advantage of this approach over conventional methods is the ability to select particular cells from a population. As a test of the reproducibility of the method and its ability to distinguish the strength of adhesion of cells to different solid surfaces, we have used it to measure the adhesiveness of human red blood cells to hydrophilic glass, tissue culture grade polystyrene, polyethylene terephthalate, and polymethyl methacrylate. We find that results for the same surface are highly reproducible and that the method is capable of distinguishing small differences in the adhesiveness of red blood cells to the above surfaces.     

Direct comparison of nanoindentation and macroscopic measurements of bone viscoelasticity

Nanoindentation has become a standard method for measuring mechanical properties of bone, especially within microstructural units such as individual osteons or trabeculae. The use of nanoindentation to measure elastic properties has been thoroughly studied and validated. However, it is also possible to assess time dependent properties of bone by nanoindentation. The goal of this study was to compare time dependent mechanical properties of bone measured at the macroscopic level with those measured by nanoindentation. Twelve samples were prepared from the posterior distal femoral cortex of young cows. Initially, dogbone samples were prepared and subjected to torsional stress relaxation in a saline bath at 37?°C. A 5 mm thick disk was subsequently sectioned from the gage length, and subjected to nanoindentation. Nanoindentation was performed on hydrated samples using a standard protocol with 20 indents performed in 20 different osteons in each sample. Creep and stress relaxation data were fit to a Burgers four parameter rheological model, a five parameter generalized Maxwell model, and a three parameter standard linear solid. For Burgers viscoelastic model, the time constants measured by nanoindentation and torsion were weakly negatively correlated, while for the other two models the time constants were uncorrelated. The results support the notion that the viscoelastic behavior of bone at the macroscopic scale is primarily due to microstructural features, interfaces, or fluid flow, rather than viscous behavior of the bone tissue. As viscoelasticity affects the fatigue behavior of materials, the microscale properties may provide a measure of bone quality associated with initial damage formation.     

Automated Micropipette Aspiration of Single Cells

This paper presents a system for mechanically characterizing single cells using automated micropipette aspiration. Using vision-based control and position control, the system controls a micromanipulator, a motorized translation stage, and a custom-built pressure system to position a micropipette (4 μm opening) to approach a cell, form a seal, and aspirate the cell into the micropipette for quantifying the cell’s elastic and viscoelastic parameters as well as viscosity. Image processing algorithms were developed to provide controllers with real-time visual feedback and to accurately measure cell deformation behavior on line. Experiments on both solid-like and liquid-like cells demonstrated that the system is capable of efficiently performing single-cell micropipette aspiration and has low operator skill requirements.     

Development of a vibratory microinjection method

To reduce cellular damage by pronuclear microinjection and nuclear transfer, we have recently developed a vibratory microinjection method. A micropipette was fixed to a piezoelectric ceramic with a resonance frequency of 70 kHz. When this micropipette was vibrated, it easily entered a mouse-fertilized egg without any sharp depression of the cell body, whereas a sharp, deep depression at the insertion site was observed when the micropipette was not vibrated. A depression rate defined as a rate of a depth of depression over an original cell diameter was utilized as an index of cellular deformation. The depression rates with and without vibration were 11.1 +/- 5.2% (N = 24) and 40.4 +/- 8.8% (N = 16), respectively (P < 0.0001, Student's t-test). In conclusion, the vibratory microinjection method is a new, useful option for gene transfer because it resulted in much less cellular deformation, therefore implicating less cellular damage.     

A Mixed-Penalty Biphasic Finite Element Formulation Incorporating Viscous Fluids and Material Interfaces

The fluid viscosity term of the fluid phase constitutive equation and the interface boundary conditions between biphasic, solid and fluid domains have been incorporated into a mixed-penalty finite element formulation of the linear biphasic theory for hydrated soft tissue. The finite element code can now model a single-phase viscous incompressible fluid, or a single-phase elastic solid, as limiting cases of a biphasic material. Interface boundary conditions allow the solution of problems involving combinations of biphasic, fluid and solid regions. To incorporate these conditions, the volume-weighted mixture velocity is introduced as a degree of freedom at interface nodes so that the kinematic continuity conditions are satisfied by conventional finite element assembly techniques. Results comparing our numerical method with an independent, analytic solution for the problem of Couette flow over rigid and deformable porous biphasic layers show that the finite element code accurately predicts the viscous fluid flows and deformation in the porous biphasic region. Thus, the analysis can be used to model the interface between synovial fluid and articular cartilage in diarthrodial joints. This is an important step toward modeling and understanding the mechanisms of joint lubrication and another step toward fully modeling the in vivo behavior of a diarthrodial joint. © 2000 Biomedical Engineering Society. PAC00: 8719Tt, 8380Lz, 8719Rr, 0270Dh, 8710+e     

梗阻性黄疸病人红细胞膜蛋白变化与力学特性的实验研究

应用ＳＤＳ－聚丙烯酰胺凝胶电泳及薄层扫描法对三种状态（梗阻状态、梗阻解除后及健康状态）下红细胞膜蛋白变化作了定性分析，证审了梗阻状态下红细胞膜蛋白带４．２有缺失，而术后又得以恢复的现象。另一方面，微管吸吮系统对上述三种状态下的红 力学特性作了测试，并用Ｖｏｉｇｔ模型分析后表明，在梗阻状态下膜的弹一模量及粘性系数增大，其变形能力下降且呈“矫枉过正”现象，最后讨论了膜蛋白４．２的存在与否与力土改一是     

A kinetic measurement of red cell deformability: a modified micropipette aspiration technique.

A kinetic measurement of the red cell deformability is developed, modifying the micropipette aspiration technique of BRAASCH (1971). The sedimented human red cells on a slide-glass are individually aspirated into a micropipette by negative pressure (delta P), and the decreasing "velocity (v)" of the applied electric current, due to the aspirating cell, is taken as a measure of the "easiness" of the cell to enter into the small orifice of the micropipette (inner diameter, 2 R congruent to 3 micrometer). An empirical relation, v infinity (pi r2) . (delta P) . ("deformability"), is obtained. In order to test the validity of the method, some factors influencing the deformability are studied: i.e., the "velocity" decreases as lowering temperature; the "velocity" of the glutaraldehyde-pretreated cells and of both in vivo and in vitro aged cells decreases. Therefore, the parameter, "velocity (v)," reflects the deformability well. In addition, if a few assumptions could be allowed, v would be related to the Young's modulus of the membrane.