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Remodeling of strain energy function of common bile duct post obstruction. 胆总管梗阻后应变能功能的重构。
Quang Dang, Hans Gregersen, Birgitte Duch, Ghassan S Kassab

Biliary duct obstruction is an important clinical condition that affects millions of people worldwide. We have previously shown that the common bile duct (CBD) undergoes significant growth and remodelling post obstruction. The mechanical stress-strain relation is expected to change due to growth and remodeling in response to obstruction and hence pressure-overload. The objective of the present study was to characterize the material properties of the CBD of the sham group and at 3 hours, 12 hours, 2 days, 8 days and 32 days (n=5 in each group) after obstruction. The Fung's exponential strain energy function was used to relate stress to strain of the normal and remodeled ducts. The Marquardt-Levenberg and genetic algorithm methods were used for the determination of material constants for the exponential strain energy function. The elastic constants obtained by the two methods did not differ (p>0.254). We obtained stable and convergent material constants at every time point. The material constant that dictates the nonlinear rate of change in the circumferential stress with respect to strain increased significantly after obstruction acutely in the first 12 hrs., decreased at 2 days and finally increased montonically during the remaining 30 days. The acute initial increase in stiffness was simply due to the elastic response. The chronic remodeling process results in an initial circumferential softening followed by stiffening of the CBD. This study has important clinical significance for patients with CBD obstruction and for endoscopists and surgeons who treat the condition.

胆管梗阻是影响全世界数百万人的重要临床疾病。我们之前的研究表明,胆总管(CBD)在梗阻后经历了显著的生长和重塑。机械应力-应变关系预计会因生长和重塑而改变,以响应阻塞和压力过载。本研究的目的是表征假手术组和梗阻后3小时、12小时、2天、8天、32天(每组n=5) CBD的材料特性。采用冯氏指数应变能函数将正常和重塑管道的应力与应变联系起来。采用Marquardt-Levenberg和遗传算法确定了指数应变能函数的材料常数。两种方法得到的弹性常数无显著差异(p>0.254)。得到了各时间点稳定收敛的材料常数。在最初的12小时内剧烈阻塞后,决定周向应力相对于应变非线性变化率的材料常数显著增加。,在第2天下降,最后在剩余的30天中呈单调上升。最初刚度的急剧增加仅仅是由于弹性响应。慢性重塑过程导致最初的周向软化,随后CBD变硬。本研究对CBD梗阻患者及内窥镜医师和外科医生治疗该病具有重要的临床意义。
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引用次数: 0
Contractile torque as a steering mechanism for orientation of adherent cells. 收缩力矩作为附着细胞方向的导向机制。
Dimitrije Stamenović

It is well established that adherent cells change their orientation in response to non-uniform substrate stretching. Most observations indicate that cells orient away from the direction of the maximal substrate strain, whereas in some cases cells also align with the direction of the maximal strain. Previous studies suggest that orientation and steering of the cell may be closely tied to cytoskeletal contractile stress but they could not explain the mechanisms that direct cell reorientation. This led us to develop a simple, mechanistic theoretical model that could predict a direction of cell orientation in response to mechanical nonuniformities of the substrate. The model leads to a simple physical mechanism--namely the contractile torque--that directs the cell toward a new orientation in response to anisotropic substrate stretching or substrate material anisotropy. A direction of the torque is determined by a dependence of the contractile stress on substrate strain. Model predictions are tested in the case of simple elongation of the substrate and found to be consistent with experimental data from the literature.

这是很好的确定,贴壁细胞改变他们的方向,以响应不均匀的底物拉伸。大多数观察表明,细胞的方向远离最大底物应变的方向,而在某些情况下,细胞也与最大应变的方向对齐。先前的研究表明,细胞的定向和转向可能与细胞骨架收缩应力密切相关,但它们无法解释指导细胞定向的机制。这使我们开发了一种简单的机械理论模型,可以预测细胞取向的方向,以响应基板的机械不均匀性。该模型推导出一种简单的物理机制——即收缩扭矩——根据基底的各向异性拉伸或基底材料的各向异性,将细胞导向一个新的方向。转矩的方向取决于收缩应力对基体应变的依赖关系。模型预测在基体简单伸长率的情况下进行了测试,发现与文献中的实验数据一致。
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引用次数: 0
On Eulerian constitutive equations for modeling growth and residual stresses in arteries. 欧拉本构方程在动脉生长和残余应力模拟中的应用。
K Y Volokh

Recently Volokh and Lev (2005) argued that residual stresses could appear in growing arteries because of the arterial anisotropy. This conclusion emerged from a continuum mechanics theory of growth of soft biological tissues proposed by the authors. This theory included Lagrangian constitutive equations, which were formulated directly with respect to the reference configuration. Alternatively, it is possible to formulate Eulerian constitutive equations with respect to the current configuration and to 'pull them back' to the reference configuration. Such possibility is examined in the present work. The Eulerian formulation of the constitutive equations is used for a study of arterial growth. It is shown, particularly, that bending resultants are developed in the ring cross-section of the artery. These resultants may cause the ring opening or closing after cutting the artery in vitro as it is observed in experiments. It is remarkable that the results of the present study, based on the Eulerian constitutive equations, are very similar to the results of Volokh and Lev (2005), based on the Lagrangian constitutive equations. This strengthens the authors' argument that anisotropy is a possible reason for accumulation of residual stresses in arteries. This argument appears to be invariant with respect to the mathematical description.

最近Volokh和Lev(2005)认为,由于动脉的各向异性,残余应力可能出现在生长的动脉中。这一结论来源于作者提出的生物软组织生长的连续介质力学理论。这个理论包括拉格朗日本构方程,它是直接根据参考位形表述的。另外,也有可能将欧拉本构方程与当前构型相结合,并将其“拉回”到参考构型。本文对这种可能性进行了探讨。本构方程的欧拉公式用于动脉生长的研究。特别是,在动脉的环形横截面上出现了弯曲产物。这些结果可能导致环在体外切割动脉后打开或关闭,正如实验中观察到的那样。值得注意的是,本研究基于欧拉本构方程的结果与Volokh和Lev(2005)基于拉格朗日本构方程的结果非常相似。这加强了作者的论点,即各向异性是动脉中残余应力积累的可能原因。就数学描述而言,这个论证似乎是不变的。
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引用次数: 0
Remodeling of strain energy function of common bile duct post obstruction. 胆总管梗阻后应变能功能的重构。
Pub Date : 2005-06-01 DOI: 10.3970/MCB.2005.002.053
Quang Dang, H. Gregersen, B. Duch, G. Kassab
Biliary duct obstruction is an important clinical condition that affects millions of people worldwide. We have previously shown that the common bile duct (CBD) undergoes significant growth and remodelling post obstruction. The mechanical stress-strain relation is expected to change due to growth and remodeling in response to obstruction and hence pressure-overload. The objective of the present study was to characterize the material properties of the CBD of the sham group and at 3 hours, 12 hours, 2 days, 8 days and 32 days (n=5 in each group) after obstruction. The Fung's exponential strain energy function was used to relate stress to strain of the normal and remodeled ducts. The Marquardt-Levenberg and genetic algorithm methods were used for the determination of material constants for the exponential strain energy function. The elastic constants obtained by the two methods did not differ (p>0.254). We obtained stable and convergent material constants at every time point. The material constant that dictates the nonlinear rate of change in the circumferential stress with respect to strain increased significantly after obstruction acutely in the first 12 hrs., decreased at 2 days and finally increased montonically during the remaining 30 days. The acute initial increase in stiffness was simply due to the elastic response. The chronic remodeling process results in an initial circumferential softening followed by stiffening of the CBD. This study has important clinical significance for patients with CBD obstruction and for endoscopists and surgeons who treat the condition.
胆管梗阻是影响全世界数百万人的重要临床疾病。我们之前的研究表明,胆总管(CBD)在梗阻后经历了显著的生长和重塑。机械应力-应变关系预计会因生长和重塑而改变,以响应阻塞和压力过载。本研究的目的是表征假手术组和梗阻后3小时、12小时、2天、8天、32天(每组n=5) CBD的材料特性。采用冯氏指数应变能函数将正常和重塑管道的应力与应变联系起来。采用Marquardt-Levenberg和遗传算法确定了指数应变能函数的材料常数。两种方法得到的弹性常数没有差异(p>0.254)。得到了各时间点稳定收敛的材料常数。在最初的12小时内剧烈阻塞后,决定周向应力相对于应变非线性变化率的材料常数显著增加。,在第2天下降,最后在剩余的30天中呈单调上升。最初刚度的急剧增加仅仅是由于弹性响应。慢性重塑过程导致最初的周向软化,随后CBD变硬。本研究对CBD梗阻患者及内窥镜医师和外科医生治疗该病具有重要的临床意义。
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引用次数: 0
Interfacial strength of cement lines in human cortical bone. 骨水泥线在人皮质骨中的界面强度。
Pub Date : 2005-06-01 DOI: 10.3970/MCB.2005.002.063
X. N. Dong, Xiaohui Zhang, X. Guo
In human cortical bone, cement lines (or reversal lines) separate osteons from the interstitial bone tissue, which consists of remnants of primary lamellar bone or fragments of remodeled osteons. There have been experimental evidences of the cement line involvement in the failure process of bone such as fatigue and damage. However, there are almost no experimental data on interfacial properties of cement lines in human cortical bone. The objective of this study is to design and assemble a precision and computer controlled osteon pushout microtesting system, and to experimentally determine the interfacial strength of cement lines in human cortical bone by performing osteon pushout tests. Thirty specimens were prepared from humeral diaphyses of four human subjects. Twenty specimens were tested under the condition of a small hole in the supporting plate, in which the cement line debonding occurred. The cement line interfacial strength ranged from 5.38 MPa to 10.85 MPa with an average of 7.31 +/- 1.73 MPa. On the other hand, ten specimens were tested under the condition of a large hole in the supporting plate, in which the shear failure inside osteons was observed. The specimens tested under the condition of the large hole resulted in an average shear strength of 73.71 +/- 15.06 MPa, ranging from 45.97 MPa to 93.74 MPa. Therefore, our results suggest that the cement line interface between osteon and interstitial bone tissue is weaker than that between bone tissue lamellae.
在人类皮质骨中,骨水泥线(或逆转线)将骨与间质骨组织分开,间质骨组织由初级板层骨的残余或重塑骨的碎片组成。已有实验证据表明水泥线参与了骨疲劳和损伤等破坏过程。然而,目前还没有关于骨水泥线在人皮质骨中的界面特性的实验数据。本研究的目的是设计和组装一个精密的计算机控制骨元推出微测试系统,并通过进行骨元推出测试来实验确定人类皮质骨中水泥线的界面强度。从4名受试者的肱骨骨干中制备了30个标本。试验选取了20个试件,在支撑板有小孔的情况下进行了水泥线脱粘试验。水泥线界面强度范围为5.38 MPa ~ 10.85 MPa,平均为7.31±1.73 MPa。另一方面,在支撑板开大孔的情况下,对10个试件进行了测试,观察了骨内部的剪切破坏。大孔条件下试件的平均抗剪强度为73.71±15.06 MPa,范围为45.97 ~ 93.74 MPa。因此,我们的研究结果表明骨细胞与间质骨组织之间的水泥线界面弱于骨组织板层之间的水泥线界面。
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引用次数: 37
On Eulerian constitutive equations for modeling growth and residual stresses in arteries. 欧拉本构方程在动脉生长和残余应力模拟中的应用。
Pub Date : 2005-06-01 DOI: 10.3970/MCB.2005.002.077
K. Volokh
Recently Volokh and Lev (2005) argued that residual stresses could appear in growing arteries because of the arterial anisotropy. This conclusion emerged from a continuum mechanics theory of growth of soft biological tissues proposed by the authors. This theory included Lagrangian constitutive equations, which were formulated directly with respect to the reference configuration. Alternatively, it is possible to formulate Eulerian constitutive equations with respect to the current configuration and to 'pull them back' to the reference configuration. Such possibility is examined in the present work. The Eulerian formulation of the constitutive equations is used for a study of arterial growth. It is shown, particularly, that bending resultants are developed in the ring cross-section of the artery. These resultants may cause the ring opening or closing after cutting the artery in vitro as it is observed in experiments. It is remarkable that the results of the present study, based on the Eulerian constitutive equations, are very similar to the results of Volokh and Lev (2005), based on the Lagrangian constitutive equations. This strengthens the authors' argument that anisotropy is a possible reason for accumulation of residual stresses in arteries. This argument appears to be invariant with respect to the mathematical description.
最近Volokh和Lev(2005)认为,由于动脉的各向异性,残余应力可能出现在生长的动脉中。这一结论来源于作者提出的生物软组织生长的连续介质力学理论。这个理论包括拉格朗日本构方程,它是直接根据参考位形表述的。另外,也有可能将欧拉本构方程与当前构型相结合,并将其“拉回”到参考构型。本文对这种可能性进行了探讨。本构方程的欧拉公式用于动脉生长的研究。特别是,在动脉的环形横截面上出现了弯曲产物。这些结果可能导致环在体外切割动脉后打开或关闭,正如实验中观察到的那样。值得注意的是,本研究基于欧拉本构方程的结果与Volokh和Lev(2005)基于拉格朗日本构方程的结果非常相似。这加强了作者的论点,即各向异性是动脉中残余应力积累的可能原因。就数学描述而言,这个论证似乎是不变的。
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引用次数: 0
Interfacial strength of cement lines in human cortical bone. 骨水泥线在人皮质骨中的界面强度。
X Neil Dong, Xiaohui Zhang, X Edward Guo

In human cortical bone, cement lines (or reversal lines) separate osteons from the interstitial bone tissue, which consists of remnants of primary lamellar bone or fragments of remodeled osteons. There have been experimental evidences of the cement line involvement in the failure process of bone such as fatigue and damage. However, there are almost no experimental data on interfacial properties of cement lines in human cortical bone. The objective of this study is to design and assemble a precision and computer controlled osteon pushout microtesting system, and to experimentally determine the interfacial strength of cement lines in human cortical bone by performing osteon pushout tests. Thirty specimens were prepared from humeral diaphyses of four human subjects. Twenty specimens were tested under the condition of a small hole in the supporting plate, in which the cement line debonding occurred. The cement line interfacial strength ranged from 5.38 MPa to 10.85 MPa with an average of 7.31 +/- 1.73 MPa. On the other hand, ten specimens were tested under the condition of a large hole in the supporting plate, in which the shear failure inside osteons was observed. The specimens tested under the condition of the large hole resulted in an average shear strength of 73.71 +/- 15.06 MPa, ranging from 45.97 MPa to 93.74 MPa. Therefore, our results suggest that the cement line interface between osteon and interstitial bone tissue is weaker than that between bone tissue lamellae.

在人类皮质骨中,骨水泥线(或逆转线)将骨与间质骨组织分开,间质骨组织由初级板层骨的残余或重塑骨的碎片组成。已有实验证据表明水泥线参与了骨疲劳和损伤等破坏过程。然而,目前还没有关于骨水泥线在人皮质骨中的界面特性的实验数据。本研究的目的是设计和组装一个精密的计算机控制骨元推出微测试系统,并通过进行骨元推出测试来实验确定人类皮质骨中水泥线的界面强度。从4名受试者的肱骨骨干中制备了30个标本。试验选取了20个试件,在支撑板有小孔的情况下进行了水泥线脱粘试验。水泥线界面强度范围为5.38 MPa ~ 10.85 MPa,平均为7.31±1.73 MPa。另一方面,在支撑板开大孔的情况下,对10个试件进行了测试,观察了骨内部的剪切破坏。大孔条件下试件的平均抗剪强度为73.71±15.06 MPa,范围为45.97 ~ 93.74 MPa。因此,我们的研究结果表明骨细胞与间质骨组织之间的水泥线界面弱于骨组织板层之间的水泥线界面。
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引用次数: 0
Contractile torque as a steering mechanism for orientation of adherent cells. 收缩力矩作为附着细胞方向的导向机制。
Pub Date : 2005-06-01 DOI: 10.3970/MCB.2005.002.069
D. Stamenović
It is well established that adherent cells change their orientation in response to non-uniform substrate stretching. Most observations indicate that cells orient away from the direction of the maximal substrate strain, whereas in some cases cells also align with the direction of the maximal strain. Previous studies suggest that orientation and steering of the cell may be closely tied to cytoskeletal contractile stress but they could not explain the mechanisms that direct cell reorientation. This led us to develop a simple, mechanistic theoretical model that could predict a direction of cell orientation in response to mechanical nonuniformities of the substrate. The model leads to a simple physical mechanism--namely the contractile torque--that directs the cell toward a new orientation in response to anisotropic substrate stretching or substrate material anisotropy. A direction of the torque is determined by a dependence of the contractile stress on substrate strain. Model predictions are tested in the case of simple elongation of the substrate and found to be consistent with experimental data from the literature.
这是很好的确定,贴壁细胞改变他们的方向,以响应不均匀的底物拉伸。大多数观察表明,细胞的方向远离最大底物应变的方向,而在某些情况下,细胞也与最大应变的方向对齐。先前的研究表明,细胞的定向和转向可能与细胞骨架收缩应力密切相关,但它们无法解释指导细胞定向的机制。这使我们开发了一种简单的机械理论模型,可以预测细胞取向的方向,以响应基板的机械不均匀性。该模型推导出一种简单的物理机制——即收缩扭矩——根据基底的各向异性拉伸或基底材料的各向异性,将细胞导向一个新的方向。转矩的方向取决于收缩应力对基体应变的依赖关系。模型预测在基体简单伸长率的情况下进行了测试,发现与文献中的实验数据一致。
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引用次数: 6
Growth, anisotropy, and residual stresses in arteries. 动脉的生长、各向异性和残余应力。
K Y Volokh, Y Lev

A simple phenomenological theory of tissue growth is used in order to demonstrate that volumetric growth combined with material anisotropy can lead to accumulation of residual stresses in arteries. The theory is applied to growth of a cylindrical blood vessel with the anisotropy moduli derived from experiments. It is shown that bending resultants are developed in the ring cross-section of the artery. These resultants may cause the ring opening or closing after cutting the artery in vitro as it is observed in experiments. It is emphasized that the mode of the arterial ring opening is affected by the parameters of anisotropy.

组织生长的一个简单的现象学理论是为了证明体积增长结合材料各向异性可以导致残余应力在动脉的积累。利用实验得到的各向异性模量,将该理论应用于圆柱形血管的生长。结果表明,在动脉的环形截面上存在弯曲产物。这些结果可能导致环在体外切割动脉后打开或关闭,正如实验中观察到的那样。强调了各向异性参数对动脉环开口模式的影响。
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引用次数: 0
Shear force at the cell-matrix interface: enhanced analysis for microfabricated post array detectors. 细胞-基质界面的剪切力:微制造柱阵列探测器的增强分析。
Pub Date : 2005-01-01 DOI: 10.3970/MCB.2005.002.001
Christopher A. Lemmon, N. Sniadecki, Sami Alom Ruiz, J. Tan, L. Romer, Christopher S. Chen
The interplay of mechanical forces between the extracellular environment and the cytoskeleton drives development, repair, and senescence in many tissues. Quantitative definition of these forces is a vital step in understanding cellular mechanosensing. Microfabricated post array detectors (mPADs) provide direct measurements of cell-generated forces during cell adhesion to extracellular matrix. A new approach to mPAD post labeling, volumetric imaging, and an analysis of post bending mechanics determined that cells apply shear forces and not point moments at the matrix interface. In addition, these forces could be accurately resolved from post deflections by using images of post tops and bases. Image analysis tools were then developed to increase the precision and throughput of post centroid location. These studies resulted in an improved method of force measurement with broad applicability and concise execution using a fully automated force analysis system. The new method measures cell-generated forces with less than 5% error and less than 90 seconds of computational time. Using this approach, we demonstrated direct and distinct relationships between cellular traction force and spread cell surface area for fibroblasts, endothelial cells, epithelial cells and smooth muscle cells.
细胞外环境和细胞骨架之间的机械力的相互作用驱动着许多组织的发育、修复和衰老。这些力的定量定义是理解细胞力学传感的重要一步。微加工后阵列探测器(mPADs)提供了细胞产生的力在细胞粘附到细胞外基质的直接测量。一种新的mPAD后标记、体积成像和后弯曲力学分析方法确定了细胞在基质界面施加剪切力而不是点矩。此外,利用柱顶和柱底的图像可以准确地从柱的偏转中分辨出这些力。然后开发了图像分析工具,以提高后质心定位的精度和吞吐量。这些研究产生了一种改进的力测量方法,使用全自动力分析系统,具有广泛的适用性和简洁的执行。新方法测量细胞产生的力,误差小于5%,计算时间小于90秒。利用这种方法,我们证明了成纤维细胞、内皮细胞、上皮细胞和平滑肌细胞的细胞牵引力与扩散细胞表面积之间存在直接而独特的关系。
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引用次数: 104
期刊
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