Interferenzmikroskopische charakterisierung von faserstrukturen, 4. Zusammenhänge zwischen der farbstoffdiffusion und der faserstruktur beim färben von polyethylenterephthalat-fasern mit dispersionsfarbstoffen

Concentration distributions of dyestuffs C. I. Disperse Red 60 and C. I. Disperse Blue 139 in microtomic cuttings of fibers of poly(ethylene terephthalate), (poly(oxyethyleneoxyterephthaloyl)) are discussed. An interpretation of the results in relation to order and orientation along the fiber radius by interferometric investigations gives informations about the diffusion process. It is shown, that the diffusion of dyestuffs in high polymers depends—in a complicated way—on fiber structure (as a function of the diffusion path), fiber history, and experimental conditions: C. I. Disperse Red 60 shows a lower diffusion rate at higher radial orientations, whereas the diffusion rate of C. I. Disperse Blue 139 does not depend on the radial dependence of these structure parameters.     

Propagation on a central fiber surrounded by inactive fibers in a multifibered bundle model

We studied uniform propagation on a central active fiber surrounded by inactive fibers in a multifibered bundle model lying in a large volume conductor. The behavior of a fully active bundle is considered in a companion paper. The bundle is formed by concentric layers of small cylindrical fibers (radius 5 μm), with a uniform minimum distance (d) between any two adjacent fibers, to yield a bundle radius of about 72μm. Individual vidual fibers are identical continuous cables of excitable membrane based on a modified Beeler-Reuter model. The intracellular volume fraction (f _i) increases to a maximum of about 90% asd is reduced and remains unchanged ford<0.01 μm. In the range ofd<0.01 μm, the central fiber is effectively shielded from external effects by the first concentric layer of inactive fibers, and a large capacitive load current flows across the surrounding inactive membranes. In addition, the fiber proximity produces a circumferentially nonuniform, current density (proximity effect) that is equivalent to an increased average longitudinal interstitial resistance. The conduction velocity is reduced asd becomes smaller in the range ofd<0.1 μm, the interstitial potential becomes larger, and both the maximum rate of rise and time constant of the foot of the upstroke are increased. On the other hand, ford>0.1 μm, there are negligible changes in the shape of the upstroke, and the, behavior of the central fiber is close to that of a uniform cable in a restricted volume conductor. Ford larger than about 1.2 μm, the active fiber environment is close to an unbounded isotropic volume conductor.     

Nano-scale analyses of the chromatin decompaction induced by histone acetylation

The acetylation of histone tails is a key factor in the maintenance of chromatin dynamics and cellular homeostasis. The hallmark of active chromatin is the hyper-acetylation of histones, which appears to result in a more open chromatin structure. Although short nucleosomal arrays have been studied, the structural dynamics of relatively long acetylated chromatin remain unclear. We have analyzed in detail the structure of long hyper-acetylated chromatin fibers using atomic force microscopy (AFM). Hyper-acetylated chromatin fibers isolated from nuclei that had been treated with Trichostatin A (TSA), an inhibitor of histone deacetylase, were found to be thinner than those from untreated nuclei. The acetylated chromatin fibers were more easily spread out of nuclei by high-salt treatment, implying that hyper-acetylation facilitates the release of chromatin fibers from compact heterochromatin regions. Chromatin fibers reconstituted in vitro from core histones and linker histone H1 became thinner upon acetylation. AFM imaging indicated that the gyration radius of the nucleosomal fiber increased after acetylation and that the hyper-acetylated nucleosomes did not aggregate at high salt concentrations, in contrast to the behavior of non-acetylated nucleosomal arrays, suggesting that acetylation increases long-range repulsions between nucleosomes. Based on these data, we considered a simple coarse grained model, which underlines the effect of remaining electric charges inside the chromatin fiber.     

The effect of muscle fiber length change on motor units potentials propagation velocity.

The influence of the muscle length on the propagation velocity of the extraterritorial action potentials was studied. Single low--threshold motor units (MUs) from m. biceps brachii, both with superficially and deeply situated fibers were investigated. The velocity of excitation propagation decreases with the muscle elongation. This dependence is not so prominent for MUs having more deeply situated fibers. In case of superficial MUs the experimentally obtained values are in better agreement with the core conductor model (v = k.square root of r), than with the linear dependence of the propagation velocity (v) on the muscle fiber radius (r) (v = k.r) observed by H?kansson (1957) on frog muscles. The observed difference between superficial and deep MUs was discussed. At least two factors may be responsible for greater changes of the excitation propagation velocity along the fibers of the superficially situated MUs during the muscle elongation. One possible factor is the essential change in the external resistance due to the decrease of distance from the fibers to the skin surface. The greater change of the muscle length during a passive muscle stretching might be another reason.     

Plastic scintillation dosimetry: optimal selection of scintillating fibers and scintillators

Scintillation dosimetry is a promising avenue for evaluating dose patterns delivered by intensity-modulated radiation therapy plans or for the small fields involved in stereotactic radiosurgery. However, the increase in signal has been the goal for many authors. In this paper, a comparison is made between plastic scintillating fibers and plastic scintillator. The collection of scintillation light was measured experimentally for four commercial models of scintillating fibers (BCF-12, BCF-60, SCSF-78, SCSF-3HF) and two models of plastic scintillators (BC-400, BC-408). The emission spectra of all six scintillators were obtained by using an optical spectrum analyzer and they were compared with theoretical behavior. For scintillation in the blue region, the signal intensity of a singly clad scintillating fiber (BCF-12) was 120% of that of the plastic scintillator (BC-400). For the multiclad fiber (SCSF-78), the signal reached 144% of that of the plastic scintillator. The intensity of the green scintillating fibers was lower than that of the plastic scintillator: 47% for the singly clad fiber (BCF-60) and 77% for the multiclad fiber (SCSF-3HF). The collected light was studied as a function of the scintillator length and radius for a cylindrical probe. We found that symmetric detectors with nearly the same spatial resolution in each direction (2 mm in diameter by 3 mm in length) could be made with a signal equivalent to those of the more commonly used asymmetric scintillators. With augmentation of the signal-to-noise ratio in consideration, this paper presents a series of comparisons that should provide insight into selection of a scintillator type and volume for development of a medical dosimeter.     

The mathematical model of insulin desorption from the bioactive, fibrous artificial store

The aim of this study was to study insulin desorption from fibrous insulin artificial store in vitro as well as in vivo, with the intention to define a mathematical model that would describe this process. Release profile of cylindrical fibrous matrixes for various insulin concentrations, desorption temperatures, time periods, and pH were presented. Change of insulin concentration in the fibers and the effect of insulin release were discussed. This model was also used to predict the optimal conditions of the release process. Possibility of predicting the effect of the fibrous store design parameters (fibre radius, amount of bonded insulin, fiber type) on the resulting insulin release rate was the major advantage of this mathematical model. Also, taking all the relevant conditions regarding these experiments into consideration, by the application of mathematical model, the diffusion coefficient during insulin release was determined.     

Finite Element Model of Mechanically Induced Collagen Fiber Synthesis and Degradation in the Aortic Valve

Tissue-engineered trileaflet aortic valves are a promising alternative to current valve replacements. However, the mechanical properties of these valves are insufficient for implantation at the aortic position. To simulate the effect of collagen remodeling on the mechanical properties of the aortic valve, a finite element model is presented. In this study collagen remodeling is assumed to be the net result of collagen synthesis and degradation. A limited number of fibers with low initial fiber volume fraction is defined, and depending on the loading condition, the fibers are either synthesized or degraded. The synthesis and degradation of collagen fibers are both assumed to be functions of individual fiber stretch and fiber volume fraction. Simulations are performed for closed aortic valve configurations and the open aortic valve configuration. The predicted fiber directions for the closed configurations are close to the fiber directions as measured in the native aortic valve. The model predicts the evolution in collagen fiber content and the effect of remodeling on the mechanical properties. © 2003 Biomedical Engineering Society. PAC2003: 8715La, 8719Rr, 8710+e, 8780Rb, 8768+z     

Analysis of the shape changes of muscle fiber cross sections in guinea pigs raised at 22°C and 5°C

Seven control and nine cold-acclimated guinea pigs were selected over a wide range of body weights (256–960 g and 239–1.074 g, respectively) from two larger groups of animals chronically exposed to 22°C or 5°C. Thin cross sections of the frozen soleus muscles were treated by the ATPase method to visualize fibers and capillaries. Photomicrographs of the sections were magnified and a total of 1,067 fiber profiles were cut out and weighed to determine individual fiber cross sectional areas (FCSA). Since most fibers are assumed to be cylinders with a circular cross section, the area of the fiber was compared to the area of a circle with the same diameter as the longest axis of the fiber. The longest axis within the fiber was measured and divided by two (LD/2). The LD/2 of each fiber was treated as the radius of a circle and the calculated area of the circle compared to the real area of the fiber. LD/2 and FCSA were positively correlated in both groups of animals by power functions FCSA=a(LD/2) ^b , wherea is the intercept andb is the regression coefficient. The values forb (1.58 for the 22°C and 1.59 for the 5°C animals) were both significantly less than 2 (b in the formula for the area of a circle), and the regression lines moved from a line representing a circle towards a line representing an ellipse, indicating that as the fibers grow they tend to become more and more elliptical. The adjusted mean of the 5°C regression line was significantly lower than that for the control line, indicating that the fibers of the cold-acclimated animals were more elliptical at the same FCSA than were the fibers of the control animals.Supported by PHS Grant No. HL18145 from the National Heart Lung and Blood Institute     

Blood flow around hollow fibers

In an artificial lung, blood is oxygenated and flows around a bundle of hollow fibers while gas flows inside the fiber. The objective of this study is to understand the hydrodynamics of three different fiber banks (inline square IS, staggered square SS and equilateral triangle ET) and to investigate the influence of both a Newtonian and non-Newtonian Casson viscosity model on the flow field. A two-dimensional finite element model for permanent, isothermal, laminar blood flow perpendicular to hollow fibers is used. All fibers are assumed identical, straight and parallel. Porosity ranges from 0.4 to 0.6 and Reynolds number varies from 1 to 60. For a given Re, ET generates less resistance than SS, the latter being comparable with IS. A lower porosity increases resistance. Non-Newtonian viscosity affects velocity patterns only at low Re (<0.5) and higher porosity (>0.5). Resistance at low Re is significantly elevated in the fiber banks due to an overall increase in viscosity. This model makes it possible to study the influence of geometry and viscosity on hydrodynamics in fiber banks and may aid in the optimization of hollow fiber artificial lung design.     

Characterization of the mechanical properties of the coronary sinus for percutaneous transvenous mitral annuloplasty

The coronary sinus (CS) vessel serves as a conduit for the deployment of percutaneous transvenous mitral annuloplasty (PTMA) devices for the treatment of functional mitral regurgitation. Characterization of the mechanical response of the CS is an important step towards an understanding of tissue–device interaction in PTMA intervention. The purpose of this study was to investigate the mechanical properties of the porcine CS using the pressure–inflation test and constitutively model the wall behavior using a four fiber family strain energy function (SEF). The results showed that the CS exhibited an S-shaped pressure–radius response and could be dilated up to 88% at a pressure of 80 mm Hg. Excellent results from model fitting indicated that the four fiber family SEF could capture the experimental data well and could be used in future numerical simulations of tissue–device interaction. In addition, a histological study was performed to identify the micro-structure of the CS wall. We found a high content of striated myocardial fibers (SMFs) surrounding the CS wall, which was also mainly composed of SMFs, while the content of smooth muscle cells was very low. Elastin and collagen fibers were highly concentrated in the luminal and outer layers and sparsely distributed in the medial layer of the CS wall. These structural and mechanical properties of the CS should be taken into consideration in future PTMA device designs.     

A coarse-grain molecular dynamics model for sickle hemoglobin fibers

The intracellular polymerization of deoxy-sickle cell hemoglobin (HbS) has been identified as the main cause of sickle cell disease. Therefore, the material properties and biomechanical behavior of polymerized HbS fibers is a topic of intense research interest. A solvent-free coarse-grain molecular dynamics (CGMD) model is developed to represent a single hemoglobin fiber as four tightly bonded chains. A finitely extensible nonlinear elastic (FENE) potential, a bending potential, a torsional potential, a truncated Lennard-Jones potential and a Lennard-Jones potential are implemented along with the Langevin thermostat to simulate the behavior of a polymerized HbS fiber in the cytoplasm. The parameters of the potentials are identified via comparison of the simulation results to the experimentally measured values of bending and torsional rigidity of single HbS fibers. After it is shown that the proposed model is able to very efficiently simulate the mechanical behavior of single HbS fibers, it is employed in the study of the interaction between HbS fibers. It is illustrated that frustrated fibers and fibers under compression require a much larger interaction force to zipper than free fibers resulting in partial unzippering of these fibers. Continuous polymerization of the unzippered fibers via heterogeneous nucleation and additional unzippering under compression can explain the formation of HbS fiber networks and consequently the wide variety of shapes of deoxygenated sickle cells.     

Interferometric evaluation of collagen concentration in tendon fibers

The dry mass concentration of collagen in native rat tail tendon fibers was studied by interferometric techniques. It could be shown that the collagen concentration of rat tail tendon fibers is not constant nor does it vary uniformly with the fiber diameter. Evidence is presented that the collagen concentration shows significant oscillations as a function of diameter. In order to explain the experimental findings, a layered model is proposed for the fiber structure; age dependent changes were also studied. It seems that the fiber structure is unaltered by ageing at the supramolecular level but its functional capacities are affected and swelling is inhibited.     

基于DT-MRI的纤维跟踪及可视化研究

磁共振扩散张量成像(DT-MRI)是一种新的成像技术,比传统的扩散加权成像(DWI)能够更加准确地反映分子扩散的方向.在脑白质这样具有大量纤维束的组织中,水分子的扩散表现出显著的各向异性,从而有可能从张量信息的各向异性入手,跟踪得到白质纤维束的走行方向.本文介绍了DTI的原理、数据采集与处理方法,提出了一种可变步长的纤维跟踪方法,并以VC /ITK/VTK为开发工具实现了DTI分析和纤维跟踪与可视化.     

从CT数据到带纤维走向的全心脏有限元模型的建立

心脏计算机模型是研究生理/病理心脏功能及心律失常治疗方法的有力工具,心脏有限元解剖模型是构建各种心脏模型的基础。从病人的临床影像数据建立个性化的心脏有限元模型,可为临床诊断治疗提供极大便利。研究一种由人体胸腔CT影像数据建立全心脏有限元模型的方法,具体步骤包括:基于胸腔CT影像,通过MIMICS建立心脏解剖面片模型;根据HyperMesh修复面片模型,得到心脏实体有限元模型。由于心肌纤维走向与心脏的电/机械活动密切相关,在从影像数据重建心脏解剖结构之后,又特别研究心肌纤维走向确定方法。首先,利用规则库方法(rule-based approach)确定心室肌纤维走向;之后,在使用规则库方法的基础上,利用结构张量分析(structure tensor analysis)进行平滑滤波,得到心房肌纤维走向。为验证心肌纤维走向的正确性,分析使用该方法计算得到的巴克曼束、左心房后部、左上心房后部、房间沟等几个典型部位处心肌纤维方向与X轴的夹角,分别为4.97°±4.84°(均值±标准差)、111.99°±3.72°、178.89°±3.73°、86.48°±4.01°,符合文献报道的心肌纤维走向的观测结果。所提出的方法可从心脏影像数据构建包含心肌纤维走向的心脏有限元模型,为各类心脏建模仿真研究打下基础。     

Composition of Muscle Fiber Types in Rat Rotator Cuff Muscles

The rat is a suitable model to study human rotator cuff pathology owing to the similarities in morphological anatomy structure. However, few studies have reported the composition muscle fiber types of rotator cuff muscles in the rat. In this study, the myosin heavy chain (MyHC) isoforms were stained by immunofluorescence to show the muscle fiber types composition and distribution in rotator cuff muscles of the rat. It was found that rotator cuff muscles in the rat were of mixed fiber type composition. The majority of rotator cuff fibers labeled positively for MyHCII. Moreover, the rat rotator cuff muscles contained hybrid fibers. So, compared with human rotator cuff muscles composed partly of slow‐twitch fibers, the majority of fast‐twitch fibers in rat rotator cuff muscles should be considered when the rat model study focus on the pathological process of rotator cuff muscles after injury. Gaining greater insight into muscle fiber types in rotator cuff muscles of the rat may contribute to elucidate the mechanism of pathological change in rotator cuff muscles‐related diseases. Anat Rec, 299:1397–1401, 2016. © 2016 Wiley Periodicals, Inc.     

Methodische Untersuchungen zur polarographischen Messung der Atmung und des „kritischen Sauerstoffdrucks” bei Mitochondrien und isolierten Zellen mit der membranbedeckten Platinelektrode

Summary In growing rats adapted to a simulated altitude of 3500 m for about 4 weeks and in their controls the evolution of cardiac ventricular weight was followed. The increase of total ventricular weight found in the adapted animals can be attributed exclusively to the increase of right ventricular weight. In other adapted and control animals cardiac capillary densities, muscle fiber diameter and external capillary radius were estimated and fiber—capillary ratio and diffusion distance were calculated. There was an increase of capillary density together with a decrease of muscle fiber density, fiber-capillary ratio and diffusion distance in the right but not in the left ventricle of the adapted rats. The muscle fiber diameters, however, were larger in both heart ventricles of the rats exposed to a simulated high altitude, especially in the right ventricle. This indicates that true hypertrophy of the muscle fibers is mainly responsible for the increase of right ventricular weight. In the left ventricle, however, a hypertrophy of the muscle fibers together with a decrease of stroma components is demonstrated. The physiological importance of the shorter diffusion distance in the right ventricle of the high altitude adapted rats is discussed and it is suggested that the shorter diffusion distance may help to keep the tissue O₂ partial pressure above the critical value, mainly also in extreme situations with high myocardial O₂ consumption.     

Two-dimensional finite element model for oxygen transfer in cross-flow hollow fiber membrane artificial lungs.

A predictive, two-dimensional model with good absolute accuracy for flow and mass transfer in cross-flow hollow fiber membrane artificial lungs is developed. The proposed model is able to predict the gas transfer to water flowing outside and perpendicular to hollow fibers in the artificial lung. The model uses a finite element technique to solve the Navier-Stokes equations and the convection-diffusion equation on the computational domain of a unit fiber cell. Subsequent stream-wise and cross-wise unit fiber cells are then coupled/assembled to the relationship between the oxygen transfer rate and flow rate of a cross-flow hollow fiber membrane artificial lung. The model is compared to experimental water data obtained by perfusing three commercial artificial lungs with water.     

立体编织构造的仿生微结构及对骨修复的促进作用

本文提出应用立体编织技术和快速成形技术分别制造支架内部结构的负型模具和外形结构的支撑模具,将多种生物材料和生长因子装配制备可降解生物仿生骨支架。设计25mm犬桡骨缺损修复实验,研究材料相同时,构造结构的支架(试验组)和均匀混合材料的支架(对照组)对骨修复的作用。结果显示两种支架均具有良好的生物相容性、骨传导和骨诱导作用。构造结构的支架明显促进新骨形成,材料内外同时降解,并引导新生组织首先在设计管道内成骨。分析认为该方法在复合多种材料时不需要高温烧结,不产热、可塑性极好,不改变材料和生长因子的性质,连通的管道保证了短时间内不同的生物材料对新骨形成作用同时存在,相互促进。     

Are the structural changes in adult Drosophila mushroom bodies memory traces? Studies on biochemical learning mutants

The pre-imaginal development of Drosophila mushroom bodies is under the influence of an unknown variable which causes populations of wild-type flies at eclosion to differ in the average number of Kenyon cell fibers. During the first week of adult life the number of adjusts to an intermediate level which depends upon the experience of the flies. Under olfactory deprivation or social isolation it reaches a lower level than under favorable rearing conditions (J. Neurogenet., 1 (1984) 113-126). The biochemical learning mutants dunce and rutabaga show no experience-dependent modulation of fiber number. In both strains the mushroom bodies of young adults seem to develop abnormally: in dunce a loss of about 600 fibers is observed, in rutabaga fiber number is low at eclosion and does not increase. The following model for long-term memory is proposed: in mushroom bodies outgrowth and decay of Kenyon cell fibers occur simultaneously. The fibers randomly form transient synapses onto extrinsic output neurons of the mushroom bodies and receive synapses from modulating neurons. Experience consolidates certain synapses, thus prolonging survival of the respective Kenyon cell fibers and increasing the steady state level of fiber number.     

Unmyelinated nerve fibers

The paper presents a critical review of various current concepts of the structure and kinetics of unmyelinated nerve fiber. A classification of nerve fibers, different from the earlier ones, is proposed, that demonstrates not only the morphological fiber types, but also the kinetics of their reversible transition stages from non-glial to myelinated fiber. Evidence is presented to show the erroneousness of conceptions, still appearing in many publications, that consider the unmyelinated nerve fiber as "the Remak's cable type fiber". According to the current data, "Remak's fiber" is a glial-neurite complex, i.e. a bundle of unmyelinated nerve fibers covered with a single glial cell. Using the electron microscope, it was demonstrated that comparable glial-neurite complexes of myelinated nerve fibers, formed in CNS in a similar way by a single oligodendrocyte, cannot be named a single fiber. Cutting the nerves makes visible that the single fibers forming "the Remak's fiber" stem from different cells, therefore they cannot be a single "fiber". It has been shown for the first time experimentally, that in extreme situations, as a result of contraction of gliocyte processes, unmyelinated fibers may "leave" the glial-neurite complexes and become the nonglial fibers. Some data are presented that may serve as criteria for differentiation of unmyelinated fiber with a stratified sheath from developing myelinated fiber.