猪降主动脉环向力学性质的实验研究

目的研究猪降主动脉的力学特性。方法猪降主动脉按照距心脏距离分成5组,各组由左右两侧组织、腹侧面组织构成。使用单轴拉伸方法拉伸组织,获得应力与伸张比曲线。采用经典数学模型分析5个部位(位置1～5)弹性、胶原纤维模量以及胶原纤维激活参数等特征,并对比腹侧面与两侧组织之间的力学差异。结果在环向上,胶原纤维模量随着远离心脏的方向逐渐增长,而弹性纤维模量位置1～4随着距心脏的距离增加而逐渐增大,位置5的弹性纤维模量减小,且位置5两侧的环向弹性纤维模量小于腹侧面约19%;在轴向上,弹性纤维模量小于腹侧面约37%,位置5腹侧面的弹性纤维模量相比于位置4差异不大(均值差异约5%)。在整个降主动脉中,侧面环向胶原纤维模量大于腹侧面约26%,环向弹性纤维模量在靠近心脏的四部分侧面高于腹侧面约16%。结论猪胸主动脉的环向力学特性和位置有关,最远端的部分在低应力下表现出较软特点。研究结果有助于科研人员更好理解主动脉的力学特征以及开展更细致的计算机建模。     

Measurement and Characterization of Whole-Cell Mechanical Behavior

An understanding of whole-cell mechanical behavior can provide insight into cellular responses to mechanical loading and diseases in which such responses are altered. However, this aspect of cellular mechanical behavior has received limited attention. In this study, we used the atomic force microscope (AFM) in conjunction with several mechanical characterization methods (Hertz contact theory, an exponential equation, and a parallel-spring recruitment model) to establish a mechanically rigorous method for measuring and characterizing whole-cell mechanical behavior in the deformation range 0–500 nm. Using MC3T3-E1 osteoblasts, measurement repeatability was assessed by performing multiple loading cycles on individual cells. Despite variability in measurements, repeatability of the measurement technique was statistically confirmed. The measurement technique also proved acceptable since only 5% of the total variance across all measurements was due to variations within measurements for a single cell. The parallel-spring recruitment model, a single-parameter model, accurately described the measured nonlinear force–deformation response (R ² > 0.99) while providing a mechanistic explanation of whole-cell mechanical behavior. Taken together, the results should improve the capabilities of the AFM to probe whole-cell mechanical behavior. In addition, the success of the parallel-spring recruitment model provides insight into the micromechanical basis of whole-cell behavior.     

可降解镁合金接骨板体内降解行为及力学性能

目的 研究可降解镁合金接骨板修复骨折过程中的降解行为及力学性能.方法 将36只成年新西兰兔随机分为实验组(镁合金接骨板组,n=18)及对照组(钛合金接骨板组,n=18),分别利用镁合金接骨板及钛合金接骨板进行骨折固定.术后通过X线片检查、扫描电镜检查、能谱分析、失重试验及4点弯曲试验,评价镁合金接骨板修复骨折过程中的降...     

Isolation and Partial Characterization of an Elastase-Like Protease from Rat Aorta Smooth Muscle Cells. Possible Role in the Regulation of Elastin biosynthesis

An elastase-like protease was isolated from rat aorta smooth muscle cells and partially characterized. It appears to behave as an intracellular enzyme and may be involved in the regulation of elastin biosynthesis.     

Mechanical Behavior of Vessel Wall: A Comparative Study of Aorta,Vena Cava,and Carotid Artery

We have used incremental stress-strain curves to study the mechanical behavior of porcine aorta, carotid artery, and vena cava. Elastic and viscous stress-strain curves are composed of low and high strain regions that are approximately linear. Analysis of the low strain behavior is consistent with previous studies that suggest that the behavior is dominated by the behavior of elastic fibers, and that the collagen and elastic fibers are in parallel networks. At high strain, the behavior is different than that of skin where it is dominated by the behavior of the collagen fibers. The high strain behavior is consistent with a series arrangement of the collagen and smooth muscle; however, the arrangement of smooth muscle and collagen may be different in aorta than in the other vessels studied. It is concluded that the mechanical behavior of the vessel wall differs from the behavior of other extracellular matrices that do not contain smooth muscle. Our results indicate that at least some of the collagen fibrils in the media are in series with smooth muscle cells and this collagen-smooth muscle network is in parallel with parallel networks of collagen and elastic tissue in aorta, carotid artery, and vena cava. It is concluded that the series arrangement of collagen and smooth muscle may be important in mechanochemical transduction in vessel walls and that the exact quantity and arrangement of these components may differ in different vessels. © 2003 Biomedical Engineering Society. PAC2003: 8719Rr, 8715La, 8719Uv, 8719Ff     

猪动脉血管的力学性能分析

目的分析不同部位动脉血管力学性能的差异,以及不同测试方法对实验结果的影响。方法根据动脉血管自身的形状特点设计独特的夹具,分别对猪胸主动脉和颈总动脉进行管状轴向/径向和片状轴向/环向方向的单轴拉伸测试,并对其力学非线性开展数据拟合分析。结果动脉血管在管状状态下拉伸获得的力学性能要强于片状状态下的拉伸结果,数值结果的差异还会随着血管管径的变小而愈加显著。结论实验结果提供了更加全面可靠的血管力学参数,为血管有限元模型和本构关系的构建提供有利数据支撑,指导组织工程血管移植物的设计制造,同时也有利于研究分析某些血管疾病潜在的病理生理,为疾病的临床治疗呈现更好的治疗效果。     

Comparisons of Planar and Tubular Biaxial Tensile Testing Protocols of the Same Porcine Coronary Arteries

To identify the orthotropic biomechanical behavior of arteries, researchers typically perform stretch-pressure-inflation tests on tube-form arteries or planar biaxial testing of splayed sections. We examined variations in finite element simulations (FESs) driven from planar or tubular testing of the same coronary arteries to determine what differences exist when picking one testing technique vs. another. Arteries were tested in tube-form first, then tested in planar-form, and fit to a Fung-type strain energy density function. Afterwards, arteries were modeled via finite element analysis looking at stress and displacement behavior in different scenarios (e.g., tube FESs with tube- or planar-driven constitutive models). When performing FESs of tube inflation from a planar-driven constitutive model, pressure–diameter results had an error of 12.3% compared to pressure-inflation data. Circumferential stresses were different between tube- and planar-driven pressure-inflation models by 50.4% with the planar-driven model having higher stresses. This reduced to 3.9% when rolling the sample to a tube first with planar-driven properties, then inflating with tubular-driven properties. Microstructure showed primarily axial orientation in the tubular and opening-angle configurations. There was a shift towards the circumferential direction upon flattening of 8.0°. There was also noticeable collagen uncrimping in the flattened tissue.     

Cell Orientation Influences the Biaxial Mechanical Properties of Fibroblast Populated Collagen Vessels

Bioartificial tissues, composed of cells in a collagen matrix, can be fabricated with preferred cell orientations to mimic the histologic arrangement of biologic tissues. The influence of preferred cell orientations on the biaxial mechanical behavior of bioartificial tissues is unknown. Characterizing the biaxial mechanical behavior is necessary for better predicting the in vivo behavior of bioartificial tissues. Fibroblast populated collagen vessels (FPCVs) were fabricated with two different cell orientations by controlling the mechanical constraints during incubation. The cell orientation was verified by confocal microscopy and the collagen fiber organization was examined by confocal reflection and scanning electron microscopy (SEM). Pressure-diameter, force-length tests were performed to determine the influence of cell orientation on the biaxial mechanical behavior. FPCVs were more extensible in the direction perpendicular to the preferred cell orientation, than in the direction parallel to the cell orientation. Biaxial tests were also performed in the presence of Cytochalasin D (Cyto D) to minimize the mechanical contribution of the cells. After Cyto D treatment, the FPCVs remained more extensible in the direction perpendicular to the cell orientation, even though a preferred collagen fiber orientation was not observed in the microscopy images.     

Characterization of a small Porcine DNA virus

Summary Characteristics of a small DNA virus isolated from kidney cell cultures of healthy 3 week-old pigs are described.The virus isolate multiplies in kidney cell cultures of pig origin, produces intranuclear inclusion bodies, and hemagglutinates guinea pig, human group 0, chicken, cat, rat and mouse red blood cells. It multiplies in pigs resulting in antibody production, but is not pathogenic for newborn hamsters and mice.The virus particle is 20–22 m in size, hexagonal in shape and without a lipid containing envelope. Buoyant density is between 1.37 and 1.38g/ml. This virus is stable within a wide range of pH, resistant to heat (56°C), against treatment with trypsin, and lipid solvents.The porcine virus was proposed as a member of the picodna virus group, and named Porcine Picodna Virus (PPV).Supported by a grant of the Common Market Research Program for control of European and African Swine Fever.     

Genomic Characterization of Porcine Rotaviruses in Italy

A total of 23 rotavirus strains isolated from pigs were analyzed. Twenty strains had been isolated from diarrheic piglets from an outbreak that occurred in northern Italy in 1983. Three strains had been isolated in 1984 from swine herds located in distinct areas of northern Italy. All 23 strains were characterized as type G6P[5] by PCR. The isolation from piglets of rotaviruses displaying typical bovine G- and P-type specificities points out the high frequency of rotavirus transmission between cattle and pigs.     

Sequential Multimodal Microscopic Imaging and Biaxial Mechanical Testing of Living Multicomponent Tissue Constructs

Understanding relationships between mechanical stimuli and cellular responses require measurements of evolving tissue structure and mechanical properties. We developed a 3D tissue bioreactor that couples to both the stage of a custom multimodal microscopy system and a biaxial mechanical testing platform. Time dependent changes in microstructure and mechanical properties of fibroblast seeded cruciform fibrin gels were investigated while cultured under either anchored (1.0:1.0 stretch ratio) or strip biaxial (1.0:1.1) conditions. A multimodal nonlinear optical microscopy-optical coherence microscopy (NLOM-OCM) system was used to delineate noninvasively the relative spatial distributions of original fibrin, deposited collagen, and fibroblasts during month long culture. Serial in-culture mechanical testing was also performed to track the evolution of bulk mechanical properties under sterile conditions. Over the month long time course, seeded cells and deposited collagen were randomly distributed in equibiaxially anchored constructs, but exhibited preferential alignment parallel to the direction of the 10% stretch in constructs cultured under strip biaxial stretch. Surprisingly, both anchored and strip biaxial stretched constructs exhibited isotropic mechanical properties (including progressively increasing stiffness) despite developing a very different collagen microstructural organization. In summary, our biaxial bioreactor system integrating both NLOM-OCM and mechanical testing provided complementary information on microstructural organization and mechanical properties and, thus, may enable greater fundamental understanding of relationships between engineered soft tissue mechanics and mechanobiology.     

mPEG-PLGA-mPEG纳米粒的体外降解规律的研究

通过开环共聚方法合成了具有不同组份的丙交酯 /乙交酯 /聚乙二醇 (LA/GA/PEG)共聚物 (PLGA PEG ,PELGA) ,并进一步偶联制得三嵌段共聚物 (mPEG PLGA mPEG ,简称PELGE)。采用超声乳化—溶剂蒸发法 (O/W )制备PELGE纳米粒 ,用紫外分光光度法测定乳酸含量的方法研究了PELGA、PELGE纳米粒体外降解规律 ,体外降解实验表明 :共聚物分子量增加 ,降解减慢 ;共聚物中GA含量增加 ,即LA/GA比例减小 ,降解加快 ;PEG含量增加 ,降解加快 ;LA/GA和PEG含量相同的PELGE比PELGA的降解速度快。证明了可通过改变LA/GA的比例或PEG的含量来调节聚合物的降解速率。     

不同降解周期下Ⅱ型胶原-丝素蛋白复合软骨支架的应力松弛行为

目的 利用有限元分析与理论模型相结合的方法,研究软骨支架在不同降解周期下的应力松弛行为。方法 基于已建立的降解本构模型计算不同降解周期下支架弹性模量;建立软骨支架有限元模型,并进行应力松弛仿真,分析支架松弛应力随时间的变化。建立应力松弛本构模型,对支架力学性能进行预测。结果 软骨支架降解14、28、42、56 d时,弹性模量分别为32.35、31.12、29.91、28.74 kPa。软骨支架各层的应力分布表现为上层受力最大;支架整体松弛应力随着时间增加先快速下降,然后趋于平稳;降解56 d时,支架能承受的应力仍在软骨的生理载荷范围内。应力松弛本构模型预测结果与有限元模拟结果吻合较好。结论 随降解时间的增加,支架弹性模量逐渐减小。降解时间越长,支架能承受的应力越小。相同降解时间下,施加的压缩应变越大,支架受力越大。有限元仿真和应力松弛本构模型可以有效预测支架降解时的应力变化。     

两种交联处理后猪小肠黏膜下层单轴拉伸性能比较

目的　寻找一种理想的猪小肠黏膜下层(small-intestinal submucosa, SIS)交联处理方法。方法　将来自同一个体的猪SIS分别进行戊二醛处理和亚甲基蓝光氧化交联处理，与新鲜组用相同的方法在万能实验机上做沿管腔纵向单轴拉伸测试，并对极限抗张强度σ(下标 max)、断裂应变ε(下标 m)和0.3MPa 应力下的弹性模量(E)处理研究。结果　三组极限抗张强度分别为(6.01±1.43)、(6.96±0.93)和(12.94±2.03)MPa，戊二醛处理后的SIS在强度上有较大改善，但是组织变得僵硬；亚甲基蓝光氧化交联处理后的SIS强度改善不是特别明显，柔韧性增强。结论　该研究首次使用戊二醛交联和亚甲基蓝光氧化交联方法对猪SIS进行了处理,并比较了与新鲜猪SIS沿管腔纵向单轴拉伸测试力学性能的差异，并证明可以发展光氧化交联方法使其成为一种有效的SIS交联手段。     

Damage Mechanics of Porcine Flexor Tendon: Mechanical Evaluation and Modeling

Porcine flexor tendons underwent cyclic and stress relaxation testing before and after strain exceeding elastic limit ("overstretch") to examine which mechanical parameters undergo changes following subfailure damage. From these data, we developed an "effective strain" damage model (in which the tendon is modeled as if being pulled to a lower strain). Damage was induced at three strain levels to determine the extent to which post-damage parameter changes were affected by overstretch strain level. We found that diffuse damage induced by overstretch decreased elastic and viscoelastic parameters obtained during testing. The stress response of tendon to strain is therefore altered following damage. We next compared the strain-dependent parameter behavior to damage-dependent behavior to determine the effective strain for each parameter. Effects of damage became more pronounced as strain during overstretch increased; following overstretch to 6.5, 9, or 13% strain, effective strain was 2.43 ± 0.33, 1.98 ± 0.3, or 0.88 ± 0.43% strain, respectively. By determining the effective strain and using it to calculate predicted values of post-damage mechanical parameters, it was possible to predict the stress relaxation behavior of tendons with Schapery's nonlinear viscoelastic model. Using this approach, a single parameter predicts both elastic and viscoelastic compromise from known, strain-dependent behaviors.     

Characterization of Lipids Associated with Macromolecules of the Intercellular Matrix of Human Aorta

Macroscopically lesion-free parts of human aortas with no or light lesions (group I) and with advanced atherosclerotic lesions (group II) were submitted to a series of successive extractions in order to “solubilize” all the macromolecular components of the arterial wall (“chemical dissection”). Lipids were extracted with methanol-chloroform from all these macromolecular fractions and analyzed for cholesterol, triglycerides, phospholipids. The fatty acid composition of the separated fractions was determined by GLC. The lipid composition and fatty acid spectrum of the macromolecular fractions of group I and group II aortas was compared.

Total lipids increased in the freely extractable (“non associated lipids, ～ 78 % of total) fraction as well as in the fraction “associated” with collagen and elastin. Free and esterified cholesterol increased also both in the “freely extractable” and in the collagen-elastin-associated lipids”, ～ 78 % of total) fraction as well was higher (+ 100 %) than that of free cholesterol (+ 60%).

Triglycerides increase also by 15 to 70 % in all fractions except in the elastin-associated fraction.

Free fatty acids increased by 40 to 400 % in all extracts associated with macromolecular fractions but not in the “freely extractable” fraction where they decreased. Phospholipids show less marked variations (～ 10 %) and decrease in the elastin associated lipids of group II aortas.

The fatty acid spectrum of group II lipids associated with macromolecules differs from that of group I. There is a relative increase of longer chains (C > 18, especially 20: 1 and 20: 2 acids). No such increase in the “long” fatty acids was seen in the “freely extractable” lipid fraction.

Elastin isolated from group II aortas is significantly enriched in total lipids, cholesterol (free and esterified) and free fatty acids and contains the widest spectrum of fatty acids (from 11:2 to 22: 1) with a significant fraction of total fatty acids as “odd” carbon chains.

There appears to be a correlation between the decrease of triglyceride-bound fatty acids and the increase of free fatty acids. The free fatty acid concentration exceeds both in group I and II aortas the concentration of fatty acid esters. This increase in free fatty acids “associated” with intercellular matrix macromolecules and especially with elastin may be the result of an increased hydrolysis of esters and/or a decreased esteri-fication in advanced atherosclerotic aortas. The accumulation of long chain and “odd” fatty acids in elastin may be an important factor in its accelerated degradation during the atherosclerotic process.     

双叶机械瓣膜不同植入角度对主动脉血流动力学的影响

目的 研究双叶机械瓣膜（bileaflet mechanical heart valve,BMHV）不同植入角度对升主动脉旋动流的影响。方法 基于1位健康自愿者主动脉CT图像,采用计算机数值模拟方法,在定常流条件下,比较研究4种不同瓣膜植入角度（0°、45°、90°和135°）对主动脉旋动流的影响。结果 BMHV植入会严重干扰主动脉内的旋动流,影响升主动脉处的旋动流结构和旋动流强度分布,在瓣膜下游出现扰流区。135°植入角度对旋动流的破坏最大,产生逆向旋动区域最多;0°和45°角植入对旋动流破坏相对较小。植入角为0°时主动脉低壁面剪切应力（<0.5 Pa）所覆盖面积最小。结论 植入角度为0°~45°时,BMHV对升主动脉内旋动流破坏相对较小。因此,对不同患者而言,应根据其主动脉（包括主动脉窦）的空间几何构型进行个性化选择,植入角度可在0°~45°之间确定。