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1.
Tendon-to-bone healing following acute injury is generally poor and often fails to restore normal tendon biomechanical properties. In recent years, the murine patellar tendon (PT) has become an important model system for studying tendon healing and repair due to its genetic tractability and accessible location within the knee. However, the mechanical properties of native murine PT, specifically the regional differences in tissue strains during loading, and the biomechanical outcomes of natural PT-to-bone healing have not been well characterized. Thus, in this study, we analyzed the global biomechanical properties and regional strain patterns of both normal and naturally healing murine PT at three time points (2, 5, and 8 weeks) following acute surgical rupture of the tibial enthesis. Normal murine PT exhibited distinct regional variations in tissue strain, with the insertion region experiencing approximately 2.5 times greater strain than the midsubstance at failure (10.80±2.52% vs. 4.11±1.40%; mean±SEM). Injured tendons showed reduced structural (ultimate load and linear stiffness) and material (ultimate stress and linear modulus) properties compared to both normal and contralateral sham-operated tendons at all healing time points. Injured tendons also displayed increased local strain in the insertion region compared to contralateral shams at both physiologic and failure load levels. 93.3% of injured tendons failed at the tibial insertion, compared to only 60% and 66.7% of normal and sham tendons, respectively. These results indicate that 8 weeks of natural tendon-to-bone healing does not restore normal biomechanical function to the murine PT following injury.  相似文献   
2.
镍钛聚髌器治疗髌骨骨折的电测分析   总被引:10,自引:0,他引:10  
应用电阻测度应变技术,得到镍钛聚髌器这一记忆合金内固定器的应力-应变关系曲线,较为精确地测定了镍钛聚髌器动态聚合加压髌骨于解剖位的生物力学力值,结果表明:镍钛聚髌器可从9个方向产生向心聚合力,纵向为主,记忆加压力值为13.67Kg,侧向为辅,永加压力值为5.19Kg,并具有一定的耐疲劳性。本实验为临床使用及指导病人术后功能锻炼提供了科学的依据,并为研究动态记忆力学下的骨愈合机理提供了实验基础。  相似文献   
3.
时间序列修订对森林二氧化碳通量的影响   总被引:3,自引:1,他引:2  
对长白山阔叶红松林2003年生长季的涡动相关实测时间序列进行了去倾修订与超声风速仪倾斜修订,并分析了不同修订方法对森林CO2通量计算值的影响.结果表明,基于未修订时间序列计算得到的森林CO2通量(Fcraw)被高估.线性与非线性去倾对Fcraw的修订量分别为1.6%、1.8%,两者差异很小.平面拟合坐标变换与流线坐标变换对Fcraw的修订量分别为3.7%、4.7%,两者差异较大.对线性去倾后的时间序列分别进行流线坐标变换与平面拟合坐标变换,二者对Fcraw的修订量分别为5.5%与4.6%.建议对时间序列进行线性去倾与平面拟合坐标变换综合修订.  相似文献   
4.
目的:探讨直立倾斜试验对儿童不明原因晕厥的诊断价值,为临床诊断提供科学依据。方法:对208例不明原因晕厥的儿童给予进行直立倾料试验检查,持续进行心电监护监测,记录其血压、心率变化,分析试验结果。结果:145例(69.71%)出现阳性的血管迷走神经反应,73例(50.34%)为血管抑制型反应;19例(13.10%)呈心脏抑制型反应;53例(36.55%)为混合型反应型,并且诱发因子多为持久站立。结论:不明原因晕厥患者在直立倾斜试验中以血管迷走反应为主,持久站立是血管迷走神经性晕厥的主要诱因。  相似文献   
5.
An analysis of the anterior patellar groove of the human femur shows considerable variation in its medial and lateral spects. The groove itself, measured by the angle it encloses, shows considerably less variation than its individual components. The suggested functional relationship between bicondylar angle and lateral elevation of the patellar groove does not obtain for this sample.  相似文献   
6.
7.
Adiponectin, a macromolecular complex similar to the members of the C1q and other collagenous homologues, elicits diverse biological functions, including anti-diabetes, anti-atherosclerosis, anti-inflammation and anti-tumor activities, which have been directly linked to the high molecular weight (HMW) oligomeric structures formed by multiples of adiponectin trimers. Here, we report the 3-D reconstructions of isolated full-length, recombinant murine C39A adiponectin trimer and hexamer of wild-type trimers (the major HMW form) determined by single-particle analysis of electron micrographs. The pleiomorphic ensemble of collagen-like stretches of the trimers leads to a dynamic structure of HMW that partition into two major classes, the fan-shaped (class I) and bouquet-shaped (class II). In both of these, while the N termini cluster into a compact ellipsoid-shaped (∼ 60 Å × 45 Å × 45 Å) volume, the collagenous domains assume a variety of arrangements. The domains are splayed by up to ∼ 90° in class I, can form a close-packed, up to ∼ 100 × 40 Å cylindrical assembly in class II, which can house about half of the 66 putative collagen-like sequence and the rest, tethered to the trimeric globular domains at the C terminus, are highly dynamic. As a result, the globular domains elaborate a variety of arrangements, covering an area of up to ∼ 4.9 × 105 Å2 and up to ∼ 320 Å apart, some of which were captured in reconstructions of class II. Our reconstructions suggest that the N-terminal structured domain, agreeing approximately with the expected volume for the octadecameric assembly of the terminal 27 amino acids, is crucial to the formation of the functionally active HMW. On the other hand, conformational flexibility of the trimers at the C terminus can allow the HMW to access and cluster disparate target ligands binding to the globular domains, which may be necessary to activate cellular signaling leading to the remarkable functional diversity of adiponectin.  相似文献   
8.
A hydrophobic pulmonary surfactant protein, SP-C, has been implicated in surface-associated activities thought to facilitate the work of breathing. Model surfactant films composed of lipids and SP-C display a reversible transition from a monolayer to surface-associated multilayers upon compression and expansion at the air/water (A/W) interface. The molecular-level mechanics of this process are not yet fully understood. The current work uses atomic force microscopy on Langmuir–Blodgett films to verify the formation of multilayers in a dipalmitoylphosphatidylcholine, dipalmitoylphosphatidylglycerol, cholesterol, and SP-C model system. Isotherms of SP-C-containing films are consistent with exclusion and essentially complete respreading during compression and expansion, respectively. Multilayer formation was not detected in the absence of SP-C. Most notable are the results from IR reflection–absorption spectroscopy (IRRAS) conducted at the A/W interface, where the position and intensity of the Amide I band of SP-C reveal that the predominantly helical structure changes its orientation in monolayers versus multilayers. IRRAS measurements indicate that the helix tilt angle changed from approximately 80° in monolayers to a transmembrane orientation in multilayers. The results constitute the first quantitative measure of helix orientation in mixed monolayer/multilamellar domains at the A/W interface and provide insight into the molecular mechanism for SP-C-facilitated respreading of surfactant.  相似文献   
9.
Generating reliable initial models is a critical step in the reconstruction of asymmetric single-particles by 3D electron microscopy. This is particularly difficult to do if heterogeneity is present in the sample. The Random Conical Tilt (RCT) method, arguably the most robust presently to accomplish this task, requires significant user intervention to solve the "missing cone" problem. We present here a novel approach, termed the orthogonal tilt reconstruction method, that eliminates the missing cone altogether, making it possible for single-class volumes to be used directly as initial references in refinement without further processing. The method involves collecting data at +45 degrees and -45 degrees tilts and only requires that particles adopt a relatively large number of orientations on the grid. One tilted data set is used for alignment and classification and the other set--which provides views orthogonal to those in the first--is used for reconstruction, resulting in the absence of a missing cone. We have tested this method with synthetic data and compared its performance to that of the RCT method. We also propose a way of increasing the level of homogeneity in individual 2D classes (and volumes) in a heterogeneous data set and identifying the most homogeneous volumes.  相似文献   
10.
The outcome of three-dimensional (3D) reconstructions in single particle electron microscopy (EM) depends on a number of parameters. We have used the well-characterized structure of the transferrin (Tf)-transferrin receptor (TfR) complex to study how specimen preparation techniques influence the outcome of single particle EM reconstructions. The Tf-TfR complex is small (290kDa) and of low symmetry (2-fold). Angular reconstitution from images of vitrified specimens does not reliably converge on the correct structure. Random conical tilt reconstructions from negatively stained specimens are reliable, but show variable degrees of artifacts depending on the negative staining protocol. Alignment of class averages from vitrified specimens to a 3D negative stain reference model using FREALIGN largely eliminated artifacts in the resulting 3D maps, but not completely. Our results stress the need for critical evaluation of structures determined by single particle EM.  相似文献   
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