人角膜的生物力学特性

以人角膜为研究对象,通过建立一套规范、系统的实验方法,揭示人角膜的生物力学特性。对人角膜标本进行了单轴拉伸实验,测定了其极限强度、应力最大时的变形能及其变形能密度;循环加载实验表明应力－应变的滞后环随加载次数的增加而逐渐减小,应力－应变曲线在应力为０．１５ＭＰａ以上时能用幂指数拟合;应力松弛实验测定了应力松弛谱各参数;蠕变实验表明归一化蠕变数据和时间对数呈线性关系     

肢体延长下软组织的生物力学特性

对羊前肢延长后和对照侧的正中神经、正中动脉、正中静脉进行应力－应变、应力松弛实验,确定其应力－应变函数和连续松弛谱的各参数。从应力－应变曲线和归一化连续松弛曲线来看,在延长停止的初期,延长后试样相对于其对照侧试样的力学特性差异较大,随着恢复时间的增加,延长后试样相对于其对照侧试样的力学特性又趋于接近,正中神经、正中动脉、正中静脉都表现出这样的规律     

紫外光-核黄素交联法对豚鼠巩膜生物力学特性的影响

目的探索紫外光-核黄素交联法对巩膜织张力和强度的影响。方法交联组和对照组皆选右眼为实验眼,交联组采用波长为（370±5）nm、辐射强度定为3.0 mW/cm2的紫外线和0.1%核黄素为光敏剂对豚鼠赤道部巩膜面进行胶原交联,对照组不进行交联处理。术后一个月取交联组交联区巩膜条带和对照组相应区域的巩膜条带,进行生物力学测试,并对眼球各组织进行HE染色光镜和透射电镜检测。结果交联组巩膜的生物力学特性增强,赤道部交联组巩膜试件断裂时的极限应力增加了147%,弹性模量显著增加了193%,极限应变降低了21.9%;后极部交联组巩膜试件断裂时的极限应力增加了108%,弹性模量显著增加了191%,极限应变降低了40.42%。HE染色光镜检查结果显示形态学无病理改变,透射电镜结果显示交联组交联区的巩膜成纤维细胞增生活跃。结论紫外光—核黄素交联法可以有效地提高巩膜的生物力学特性,增强巩膜组织的张力和强度,有望作为治疗高度病理性近视的一种方法。     

激光作用的皮肤生物力学试验研究和机理分析

激光能明显影响皮肤的生物力学性能。通过选择与人体皮肤力学性能相似的离体猪皮进行不同加载方式的拉伸试验,可以研究皮肤的拉伸强度、应力应变关系、皮肤各向异性、取样部位影响、激光作用影啊、反复加卸载,松弛效应等受力性能,分析激光作用的皮肤生物力学模型及皮肤受力和修复机理,并在本构模型中引入激光影响因素。试验发现,一定强度的激光可以改善皮肤弹性,且不影响其粘滞效应和松弛速率。     

软组织扩张下的生物力学特性

对狗后肢扩张后和对照侧的隐神经、隐动脉、隐静脉进行应力－应变、应力松驰实验,确定其应力－应变函数和连续松驰谱的各参数。从应力－应变曲线和归一化连续松驰曲线来看,在扩张后的短时期内,随着扩张器注水量的增加,扩张后样品的力学特性相对于其对照侧样品的特性又趋于接近,隐神经,隐动脉,隐静脉都表现出这样的规律。     

离体心舰顺应性综合评定的实验研究

采用精度高、稳定性好的标准等长收缩灌流装置,从数学和弹性力学角度计算、分析正常及缺氧状态下大鼠乳头肌的应力-应变、应力松弛和蠕变三种生物物理特性的变化。以前者反映顺应性的静态变化,尝试以后二者反映顺应性的动态变化。结果表明,缺氧状态下,不仅心肌的静态顺应性降低(应力—应变曲线明显左移),其动态顺应性也明显降低(应力松驰及蠕变的程度和速度明显降低)。结果提示,本实验方法可用于不同状态下离体心肌顺应性的综合评定。     

大鼠离体心肌粘性劲度定量评定的研究

本实验依据心肌工作模型和心肌顺应性的理论,从大鼠离体心肌静态、动态应力-应变指数曲线和应力松弛对数曲线中,求得反映心肌粘性劲度的指标η_1和η_2,并对心肌组织粘性成分的粘性劲度进行了定量评定。η_1和η_2值与心肌粘性劲度呈同向性变化、且重复性好。本工作提示,η_1和η_2可作为实用可靠的定量评定心肌顺应性的指标。     

双层滑动型接骨板的生物力不分析与临床应用

临床实践证明双层滑动型接骨板治疗四肢长骨骨折是疗效较好的内固定方法。本文从生物力学角度对24具湿润新鲜尸体股骨进行力学试验。测定了骨折固定部位的应力、应变、位移的分布，证明了这种固定方法是符合生物力学原理的，从载荷、应力、位移等一系列曲线表明它的松动、移位，钉板断裂很少发生，它能促进新骨生长和加速骨折愈合。     

不同周期性应变对间充质干细胞形态变化的影响

目的探讨不同周期性应变对骨髓间充质干细胞（mesenchymal cells,MSCs）细胞形态变化的影响。方法根据应变的大小实验分为5组,Ⅰ组（静态培养）、Ⅱ组（1%应变）、Ⅲ组（3%应变）、Ⅳ组（10%应变）、Ⅴ组（15%应变）;10μg/mL细胞松弛素B（Cytochalasin B,CB）作用细胞1 h后,设相同的组进行平行实验,作用时间12 h,拉伸频率0.25 Hz;根据应变的作用时间实验分为3组,Ⅰ组（静态培养）、     

不同应变对骨髓间充质干细胞系细胞骨架影响的研究

目的:探讨不同应变对骨髓间充质干细胞系细胞骨架形态的影响。方法:实验分为六组,Ⅰ组(静态培养)、Ⅱ组(静态培养 细胞松驰素B)、Ⅲ组(10%应变12h)、Ⅳ组(10%应变12h 细胞松驰素B)、Ⅴ组(10%应变24h)、Ⅵ组(10%应变24h 细胞松驰素B)。分别对其施加10%0.5Hz的周期性应变,采用激光共聚焦显微镜技术和考马斯亮蓝染色方法对小鼠骨髓间充质干细胞系(D1细胞)细胞骨架进行形态观察、细胞F-肌动蛋白表达定量分析。结果:细胞受到不同周期性应变后,细胞的排列方向发生改变,细胞内的F-肌动蛋白排列同细胞的方向一致,随着拉伸时间的延长,F-肌动蛋白发生部分的断裂,F-肌动蛋白的荧光强度同静态组相比明显减弱(P<0.01);当加入细胞松驰素B后,细胞内F-肌动蛋白结构发生改变,在力的作用下,细胞内微丝断裂明显,随着拉伸时间的延长,微丝断裂更为加剧,F-肌动蛋白的荧光强度同静态组相比显著减弱(P<0.01)。结论:不同周期性应变对细胞微丝结构产生一定的影响,微丝在细胞感应力的响应中起重要作用。     

实验性羊胫骨骨折愈合生物力学研究

本实验用山羊10只,线锯造成胫骨中部骨折,夹板固定。于术后2、4、6周分别处死动物。测量其胫骨骨折愈合的极限弯曲载荷。结果表明:(1)术后第2周,因为纤维性骨痂,无弯曲载荷测量;(2)术后第4周,极限弯曲载荷是150±24(N),其断裂发生在原骨折线,(3)术后第6周,原骨折线处不再发生断裂,干骺部出现断裂,其极限弯曲载荷为653±55(N)。这些结果对临床骨科是有意义的。     

An experimental approach to modeling the strength of canine teeth

The strength of canine teeth in several carnivores is found through direct fracture experiments. The average forces required to break the canines of adult animals are coyote 1170 N, red fox 533 N, bobcat 737 N and raccoon 512 N. Stresses created in teeth at the breaking load are predicted by finite-element analysis and beam theory. The ultimate tensile stress sustainable in these teeth is 338 MPa in adult animals. The large pulp cavity in the canines of young animals significantly weakens the bases of their teeth (by about 25%), but as the animal ages the pulp cavity decreases and has little effect on overall tooth strength. The tooth material of young of the year is significantly weaker than that from older animals (by about 35%). With the experimentally derived ultimate tensile stress, finite-element analysis can estimate the breaking load of canines for several carnivores. A significant allometric relationship exists between log of body weight and log of strength of tooth (slope=0.81).     

Effects of postmortem storage by freezing on ligament tensile behavior

The purpose of this study is to examine the effect of prolonged postmortem freezing storage (between 1 1/2 and 3 months at -20 degrees C) on the structural properties of the medial collateral ligament (MCL)-bone complex as well as the mechanical properties of the MCL substance from the rabbit knee. Tensile testing of the femur-MCL-tibia specimen was performed and no statistically significant changes were noted between the fresh and stored samples in terms of the cyclic stress relaxation, the load-deformation characteristics, as well as the load, deformation and energy absorbing capability at failure. The area of hysteresis of the stored samples was significantly reduced in the first few cycles, however. The mechanical properties of the MCL substance, as represented by the stress-strain curves, tensile strength and ultimate strain also did not change following storage. We conclude, therefore, proper and careful storage by freezing would have little or no effect on the biomechanical properties of the ligaments.     

Mechanical properties of UV irradiated rat tail tendon (RTT) collagen

The mechanical properties of RTT collagen tendon before and after UV irradiation have been investigated by mechanical testing (Instron). Air-dried tendon were submitted to treatment with UV irradiation (wavelength 254 nm) for different time intervals. The changes in such mechanical properties as breaking strength and percentage elongation have been investigated. The results have shown, that the mechanical properties of the tendon were greatly affected by time of UV irradiation. Ultimate tensile strength and ultimate percentage elongation decreased after UV irradiation of the tendon. Increasing UV irradiation leads to a decrease in Young's modulus of the tendon.     

Two modified techniques for flexor tendon repair.

The aim of this article is to present two new techniques for digital flexor tendon repair: a modification to the conventional Kessler technique (wrap core suture) and tendon splints (H-shaped splint). These techniques were aimed at enhancing the biomechanical properties of such repairs as related to resistance to both gap formation and repair failure. Comparing (in an ex vivo study) the tensiometric properties (gap formation and failure strengths) of 24 flexor digitorum profundus tendons repaired with the described techniques (12 repairs per each technique) and the conventional Kessler repair (24 repairs), we found that the former provided significantly stronger repairs than the latter in vitro. A statistically significant difference (p < 0.001) was found between each of the two presented techniques and the Kessler repair. The wrap core suture increased the load at which a visible (1 mm) gap formed by 22.6 percent when compared with the conventional Kessler suture. The mean gap strength of the wrap core repair was 6.5 N, whereas that of the conventional Kessler was 5.3 N. The failure loads (ultimate strength) of the wrap core suture were 33.8 percent higher than those of the conventional Kessler. The mean breaking load of the wrap core repair was 19.4 N, whereas that of the conventional Kessler was 14.5 N. The H-splint repair increased the load at which a visible gap formed and the failure loads (ultimate strength) by 158.5 and 333.1 percent, respectively, when compared with the conventional Kessler suture. The mean gap strength of the H-splint repair was 13.7 N, and its mean breaking load was 62.8 N.     

The Topology of the Energy Landscapes of Macromolecules in the Torsion Angle Space and the Principle of the Minimum Energy Dissipation Rate in Conformational Relaxation

This article discusses some basic problems of structural biology and molecular dynamics simulation methods that need to be taken into account when considering, the protein folding problem, and prediction of 3D-structures for biopolymers. A multidimensional Fourier series expansions were formulated for the energy landscapes of the systems with conformational mobility, These energy landscape representations are correct from the viewpoint of the topology of the macromolecule configuration spaces. The problem of the single global minimum on the energy landscape for proteins is discussed and is formulated in tems of phase rules for the component of Fourier expansions. This rule is formally similar to the problem of diffraction on a multidimensional cubic lattice. The calibration of biopolymer force fields and their correspondence to topologically correct energy landscapes are discussed. Equations of motion were obtained in a matrix form for the relaxation of a representative point position on a multidimensional potential energy surface. The solutions of the equations for conformational relaxation were shown to obey the principle of the minimum energy dissipation rate at a given relaxation rate of potential energy (or folding rate).     

Strength of mid-logarithmic and stationary phase Saccharopolyspora erythraea hyphae during a batch fermentation in defined nitrate-limited medium

A method for measuring mechanical properties of Saccharopolyspora erythraea is reported with data from a batch fermentation. Briefly, hyphae were glued to the end of a tungsten filament mounted horizontally on a sensitive force transducer. Free ends of hyphae were trapped against a flat surface by a second probe. The force transducer and tungsten filament were then moved at a fixed rate, the hypha were strained, and the force resisting motion recorded. From these data the maximum force resisting motion is taken as the force at which breakage occurs. Hyphae from the mid-logarithmic phase of a simple batch fermentation on defined medium were found to have a breaking force of 890 +/- 160 nN (95% confidence), while stationary phase hyphae were weaker at 580 +/- 150 nN. Video recordings of the experiments allowed an approximation of breaking strain, which did not differ significantly between samples at 0.18 +/- 0.03. Electron microscopy was used to measure cell wall thickness, cell diameter, and hence cell wall cross-sectional area. The ultimate tensile strength was estimated to be 24 +/- 3 MPa with no difference between the two samples, the lower breaking force of the stationary phase hyphae being attributed to a thinner cell wall. Assuming a linear relationship between stress and strain, the elastic modulus was estimated to be 140 +/- 30 MPa. These values are comparable with other structural biological materials such as yeast cell walls and collagen.     

Globule-coil transition of denatured globular protein investigated by a microwave dielectric technique

A mechanism for the gel-glass transition of denatured globular protein has been explained from the viewpoint of the globule-coil transition with microwave dielectric measurements using a time domain reflectometry (TDR) method. Boiled egg white, which is an aqueous gel of egg white prepared by heat treatment at 100 degrees C, becomes a glass on drying. In the gel state, the relaxation processes corresponding to the orientation of bulk water and the micro-Brownian motion of peptide chains of denatured protein were observed around 10 GHz and 10 MHz, respectively. When the gel-glass transition occurred, the relaxation strength for bulk water decreased rapidly as evaporation and breaking of water structure occurred. Simultaneously, the relaxation strength for micro-Brownian motion increased abruptly, as the structure of globular protein varied from globule state to coiled state. It is considered that the protein molecule spreads out and takes up a coiled state by reductions of hydrophobic and hydrophilic interactions of the globular protein. These reductions occur through a decrease in the amount of water.