Journal of Biomechanical Science and Engineering
Online ISSN : 1880-9863
ISSN-L : 1880-9863
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62件中41～40件の論文を表示しています
  • 10 巻 (2015) 3 号 p. 15-00423
    Muscle stress generated in the forearm during hand gripping
    Saran KEERATIHATTAYAKORN, Satoshi YAMADA, Shigeru TADANO
    The authors proposed an electromyography computed tomography (EMG-CT) method to measure the distribution of muscle activity in the forearm using surface EMG signals from multiple surface electrodes. The present study is to develop a method to estimate muscle stress, i.e., force generated during contraction per unit area in the whole cross-section of the forearm based on EMG-CT. While three subjects performed hand gripping trials using three hand grip devices, EMG signals around the forearm were measured using EMG-CT. An EMG conduction model of the forearm was constructed using an outline geometry of the subjects' forearm which was measured with a handy 3D scanner. The stress of muscle was calculated from the relationship between gripping force and total muscle activity. As a result, the distribution of muscle stress in the forearm during hand gripping was visualized in a tomographic image. It was clear that the stress was concentrated in the flexor digitorum superficialis, flexor digitorum profundus, flexor carpi radialis, and extensor digitorum communis region. The maximum stress in the forearm muscles increased from 0.08 ± 0.01 to 0.18 ± 0.02 MPa when gripping force increased from 77 to 242 N. This study provides a novel method of measuring muscle stress in forearm.
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  • 10 巻 (2015) 1 号 p. 14-00265
    Investigation of characteristic hemodynamic parameters indicating thinning and thickening sites of cerebral aneurysms
    Daichi SUZUKI, Kenichi FUNAMOTO, Shinichiro SUGIYAMA, Toshio NAKAYAMA, Toshiyuki HAYASE, Teiji TOMINAGA
    Cellular and animal experiments and computational fluid dynamics (CFD) have revealed that mechanisms of the initiation, growth and rupture of a cerebral aneurysm are related to hemodynamics. By direct observation of a cerebral aneurysm during craniotomy, thinning or thickening sites can be found on the aneurysmal wall. The thinning site of a cerebral aneurysm is considered to be at high risk of rupture. In addition, the thickening site of a cerebral aneurysm is not necessarily in a stable state since arteriosclerosis may have occurred. Hence, information on wall conditions, i.e., thinning and thickening, of a cerebral aneurysm is beneficial for clinical diagnosis and treatment. In this study, a hemodynamic parameter to effectively estimate the thinness or thickness of cerebral aneurysmal walls was investigated. CFD of hemodynamics in cerebral aneurysms developed at the anterior communicating artery (ACoA), a common site of cerebral aneurysms, was performed, and characteristic distributions of hemodynamic parameters were investigated by comparing the computational results with clinical images. As a result, a high value of the time-averaged wall shear stress (TAWSS) was found to be present at thinning sites, while a low TAWSS and a high relative residence time (RRT) of an indicator of blood retention were observed at thickening sites. Thinning and thickening sites each have their own characteristics distribution of hemodynamic parameters.
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  • 9 巻 (2014) 2 号 p. 13-00163
    Nonlinear mechanical analysis of posterior spinal instrumentation for osteoporotic vertebra: Effects of mechanical properties of the rod on the failure risks around the screw
    Daisuke TAWARA, Kenta NORO, Tetsuya TSUJIKAMI, Yoshiyuki OKAMOTO, Hideki MURAKAMI
    In spinal fusion with instrumentation for the treatment of osteoporotic vertebral fracture, it is common for pedicle screws, which are inserted into vertebrae and strongly immobilized by a rigid rod, to loosen and dissociate. One of their expected causes is failure and reduction of fixity around a screw. An improved rod with a damper structure has thus been proposed to increase the freedom of movement of the rod and allow more flexible fixation of the spine. To evaluate the availability of the proposed structure and establish appropriate improved design of screws and rods with fewer occurrences of loosening and dissociation, effects of the structural change to the improved rod on the distribution of failure risks around the screw need to be investigated. In the present study, we performed nonlinear fracture analysis for spinal instrumentation surgery using an osteoporosis model and evaluated the failure distribution in the vertebrae while changing the apparent stiffness of the damper joint. Our finite element analysis showed that there were few expected failures in the flexible fixation model, indicating the effectiveness of the improved structure of the rod in reducing the loosening and dissociation of screws. It also suggested that the reduction was derived from the allowance of horizontal deformation in the damper joint in the improved rod. The potential of the structural improvement and the mechanism responsible for reducing the risks of loosening and dissociation are discussed.
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    ★Paper of the Year 2014

  • 9 巻 (2014) 1 号 p. JBSE0002
    Numerical analysis of arterial contraction regulated by smooth muscle stretch and intracellular calcium ion concentration
    Naoki KIDA, Taiji ADACHI
    In this study, for a better understanding of arterial functions, we examine the effects of active stresses, which are generated by contractile units included in smooth muscle cells, on the stress distribution in the arterial wall. Thus far, it is widely recognized that active stress generation is regulated by mechanical and chemical operations, i.e., both smooth muscle stretch and intracellular calcium ion concentration. Based on this fact, we develop an arterial wall model with active stresses that couples the mechanical and chemical ones suitable for the finite element method. By using this coupled model within the framework of finite element analysis, we calculate the stress distribution including active stresses at a prescribed intracellular calcium ion concentration. The results show that as the intracellular calcium ion concentration increases, the effect of active stress appears continuously, i.e., stress distribution could be considered as a continuous function of the intracellular calcium ion concentration. To obtain stress distributions at the prescribed intracellular calcium ion concentration, which is assumed to be reached as a result of active calcium ion transport under various in vivo conditions, are meaningful as a preliminary step in developing advanced models considering the active calcium ion transport systems.
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  • 9 巻 (2014) 1 号 p. JBSE0007
    Non-invasive detection of matrix-producing chondrocytes in tissue-engineered cartilage by second-harmonic-generation microscopy
    Reiko MAEHARA, Shuichiro FUKUSHIMA, Masahiro KINO-OKA, Tsutomu ARAKI
    Noninvasive quality evaluation methods that make it possible to monitor culture processes are ideal for tissue-engineered cartilage made of autologous chondrocytes and collagen gel. However, usual methods are quite invasive because the products are examined chemically and observed histologically with dye. Here we employed second-harmonic-generation (SHG) microscopy, which can be used to observe collagen without any preparation such as staining or fixing. We demonstrated SHG imaging of tissue-engineered cartilage composed of rabbit chondrocytes and type I collagen gel. Our results showed that aggregations of round cells that produced type II collagen were observed as spherical dark spaces in the SHG images. The volumes of these spaces were related to the numbers of cells in the aggregations. These results indicate that we can estimate the number of the matrix-producing cells by SHG imaging. Because SHG microscopy is a noninvasive method, it is suitable for evaluating the quality of tissue-engineered cartilage and also for quality control during the manufacturing process.
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  • 8 巻 (2013) 2 号 p. 114-128
    The Stabilization Effect of Mesenchymal Stem Cells on the Formation of Microvascular Networks in a Microfluidic Device
    Kyoko YAMAMOTO, Kohei TANIMURA, Yo MABUCHI, Yumi MATSUZAKI, Seok CHUNG, Roger D. KAMM, Mariko IKEDA, Kazuo TANISHITA, Ryo SUDO
    There is a demand for three-dimensional (3D) angiogenesis model including endothelial cells (ECs) and mesenchymal stem cells (MSCs), which are known to differentiate into pericytes, to construct stabilized and matured microvascular networks in vitro. However, it remains to be elucidated how MSCs affected on ECs in the process of 3D angiogenesis. In this study, we utilized a microfluidic device to develop a 3D coculture system including human umbilical vein ECs and human MSCs, which allowed us to investigate the effects of MSCs on ECs in the context of 3D angiogenesis. A series of EC:MSC ratio was tested in the EC-MSC coculture. First, we confirmed that MSCs differentiated into pericytes by direct EC-MSC contacts. Next, we found that MSCs attenuated vascular sprout formation of ECs regardless of EC:MSC ratio in the early stage of 3D angiogenesis as well as extension of microvascular networks in the later stage. ECs and MSCs were also cultured under interstitial flow to enhance angiogenesis. However, the stabilization effects of MSCs on the extension of capillary structures were dominant over the promotion effects of the interstitial flow. These results indicate the stabilization effect of MSCs on the formation of microvascular networks in vitro. Although some HMSCs differentiated into pericytes and located around microvascular networks, vascular structures became thick over time in coculture. The 3D EC-MSC coculture model described in this study is useful to further investigate culture microenvironments for constructing stabilized and matured microvascular networks with aligning pericytes.
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  • 8 巻 (2013) 4 号 p. 306-318
    Experimental and Analytical Studies on Contact Irreversible Electroporation for Superficial Tumor Treatment
    Kosaku KURATA, Ryo UENO, Masahiro MATSUSHITA, Takanobu FUKUNAGA, Hiroshi TAKAMATSU
    Irreversible electroporation (IRE) is attracting much attention as a less-invasive therapy to ablate abnormal tissues. With a pair of electrodes inserted into the tissue, the IRE perforates the targeted cells non-thermally by a train of intensive electric pulses that exceeds a certain threshold. Since only the cells are necrotized percutaneously, the extracellular matrix is kept intact in the IRE, which is favorable for prompt tissue regeneration. In this study, we demonstrated that the IRE is also applicable to treat superficial targets such as melanoma, nevus, and tumors on gastrointestinal surface. A pair of 1-mm dia. stainless steel rods fixed 5 mm apart in an acrylic plate was contacted on an agarose gel containing fibroblasts. A sequence of 15 to 90 pulses of 1 kV was then applied to the gel via electrodes. All pulses were 10 μs in length and oscillated at 100 ms intervals. The boundary between dead and alive cell regions was determined at the surface and vertical cross section by using fluorescent staining. The necrotic cell area was also predicted by a numerical solution to the equation of electric field. Those determined with an assumption that the potential difference of 1 V between the cell membrane induces irreversible cell breakdown agreed well with the necrotic cell area and maximal depth in the experiment at low pulse number. However, the experiment showed the increase in the necrotic area with increasing the pulse repetition. Since application of multiple pulses perforates the highly resistive cell membrane, our study indicated the importance of taking into account the change in the electrical properties due to cell destruction.
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  • 8 巻 (2013) 4 号 p. 344-355
    Ground Effect in Fruit Fly Hovering: A Three-Dimensional Computational Study
    Masateru MAEDA, Hao LIU
    In very few studies it is shown that an increase in vertical force can be achieved when a flapping-wing hovers in ground effect (IGE). The body, however, has usually been neglected and its influence on three-dimensional vortex structures and consequent aerodynamic forces is still unclear. In this study we carried out a computational fluid dynamic study of a fruit fly (Drosophila melanogaster) hovering for two cases: “in ground effect” and “out of ground effect” (OGE), where the heights from the ground are less than one and more than five times the wing length, respectively. The wings in the IGE computation generated merely 0.7% larger wingbeat cycle-averaged vertical force than in the OGE condition. The body, in contrast, exhibited a significant increase in the vertical force: when out of ground effect, the average vertical force of the body was almost zero (-0.0025 μN); whereas in ground effect, the force increased to 0.78 μN, which is the major contributor to the 8.5% increase in the total vertical force (from 9.9 μN at OGE to 10.8 μN at IGE). Meanwhile, the aerodynamic power of the wings decreased by 1.6%, resulting in a 10% improvement in the overall vertical force-to-aerodynamic power ratio. The flow-field visualization revealed that the downwashes generated by the wings create a high pressure “air cushion” underneath the body, which should be responsible for the enhancement of the body vertical force production. Our results point to the importance of the presence of body in predicting the vertical forces in flapping flights in ground effect.
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  • 7 巻 (2012) 2 号 p. 130-140
    Dynamic Changes of Traction Force at Focal Adhesions during Macroscopic Cell Stretching Using an Elastic Micropillar Substrate: Tensional Homeostasis of Aortic Smooth Muscle Cells
    Kazuaki NAGAYAMA, Akifumi ADACHI, Takeo MATSUMOTO
    In order to determine how cells change their traction forces at focal adhesions (FAs) under macroscopic deformation conditions, we investigated the dynamic changes in traction force at FAs by culturing porcine aortic smooth muscle cells (SMCs) on elastic micropillar substrates and giving them macroscopic deformation by stretching the substrates. We patterned adhesion region on the top surface of a polydimethylsiloxane-based micropillar array using our original micropatterning technique to align the cells on the pillar array parallel to the stretch direction. SMCs plated on the micropillars successfully spread in the adhesion region and their actin stress fibers (SFs) aligned in the direction to be stretched. Cells were then stretched and released cyclically with strain rates of 0.3%/15s up to 3—6% strain, and deflection of micropillars at both side regions of cells were measured simultaneously to obtain the traction force at each FA in situ. SMCs aligned in the stretch direction showed two types of responses: almost a half of the SMCs changed their force in phase with the applied strain, and showed gradual active contraction with the stretch cycles (synchronous group); and the rest tended to keep their force constant and became elongated with the cycles (asynchronous group). In the asynchronous group, the force sometimes changed in antiphase with the cell strain as if the cells maintain intracellular traction force at a constant level. These results may indicate that SMCs sometimes exhibit active homeostatic responses to keep their pretension constant during macroscopic stretching, and such tensional homeostatic responses may occur concurrently with cell elongation.
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  • 7 巻 (2012) 2 号 p. 188-198
    High Time Resolution Time-Lapse Imaging Reveals Continuous Existence and Rotation of Stress Fibers under Cyclic Stretch in HUVEC
    Yusuke MITSUOKA, Akira TSUKAMOTO, Shunsuke IWAYOSHI, Katsuko S. FURUKAWA, Takashi USHIDA
    Cells under cyclic stretch sense their environments and induce responses such as actin stress fiber (SF) reorientation and morphological changes. These physiological responses are thought to occur when cells sense incompatibility between SF orientation and stretching direction. This hypothesis requires existence of SFs. However, such existence of SFs in cells under cyclic stretch remains unclear since few studies attempted to track the existence of SFs throughout cyclic stretch. In order to track the existence of SFs throughout cyclic stretch, high time resolution time-lapse imaging was improved in two points. First, SFs were clearly imaged with coexpression of DsRed-zyxin and GFP-actin. Second, time resolution was improved so that fluorescence images were obtained every 28 sec. With the improved high time resolution time-lapse imaging, it was revealed, for the first time, that SFs could exist continuously throughout cyclic stretch. Moreover, physiological responses including morphological change as well as SF reorientation occurred during the time when SFs formed incompatibility between SF orientation and stretching direction. These results demonstrated that SFs continuously existed in cells under cyclic stretch and in turn suggested that continuous presence of incompatibility between orientation of long-lasting SFs and the stretching direction might be important for mechanosensing which induces physiological responses.
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  • 7 巻 (2012) 1 号 p. 57-71
    Parallel Simulation of Cellular Flow in Microvessels Using a Particle Method
    Davod ALIZADEHRAD, Yohsuke IMAI, Keita NAKAAKI, Takuji ISHIKAWA, Takami YAMAGUCHI
    We developed a numerical method for large-scale simulations of cellular flow in microvessels. We employed a particle method, where all blood components were modeled using a finite number of particles. Red blood cell deformation was modeled by a spring network of membrane particles. A domain decomposition method was used for parallel implementation on distributed memory systems. In a strong scaling test up to 64 CPU cores, we obtained a linear speedup with the number of CPU cores, and demonstrated that our model can simulate O(103) red blood cells in vessels a few tens of micrometers in diameter. For quantitative validation, we analyzed the Fåhræus effect and the formation of a cell-depleted peripheral layer. Simulations were performed for tube hematocrit ranging from 20 to 45%, and microvessel diameters from 9 to 50 µm. Our numerical results were in good agreement with previous experimental results both for the discharge hematocrit and cell-depleted peripheral layer thickness.
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  • 6 巻 (2011) 1 号 p. 40-48
    Surface Morphology and Stiffness of Cartilage-Like Tissue Repaired with a Scaffold-Free Tissue Engineered Construct
    Ryosuke NANSAI, Takuya SUZUKI, Kazunori SHIMOMURA, Wataru ANDO, Norimasa NAKAMURA, Hiromichi FUJIE
    We have been developing a new tissue engineering technique for cartilage repair using a scaffold-free tissue engineered construct (TEC) bio-synthesized from synovium-derived mesenchymal stem cells (MSCs). A round-shaped chondral defect of 8.5 mm in diameter and 2.0 mm in depth created on the medial condyle of immature (4-month-old) and mature (12-month-old) porcine femur was filled with the TEC. Six months after surgery, a cylindrically shaped specimen of 4 mm in diameter and 4-5 mm in depth was extracted. Stiffness measurements were carried out on the specimen using an AFM after the surface image of the specimen was obtained. The TEC-treated tissues exhibited more irregular surface as compared with normal cartilage, regardless of animal maturity. The stiffness of the superficial layer of the TEC-treated tissue was significantly lower than those of the normal cartilage, indicating 6.8±2.3 mN/m in the immature group and 8.8±2.3 mN/m in the mature group. Histological observation indicated that the defects were repaired with a hyaline cartilage-like tissue with positive Safranine O staining, regardless of animal maturity. However, the superficial layer of the repaired tissues was negatively stained with Safranine O. The present study suggests that the recovery of the superficial layer is delayed in both immature and mature animals although the treatment with TEC enhances the repair of partial chondral defects.
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  • 6 巻 (2011) 2 号 p. 114-124
    Residual Stress Distribution in the Bovine Femoral Diaphysis Measured by Synchrotron
    Satoshi YAMADA, Shigeru TADANO, Masahiro TODOH, Kazuhiro FUJISAKI
    The presence of residual stresses in bone tissue has been noted, and the authors have reported that there are residual stresses in bone tissue. The tensile residual stresses in the bone axial direction on the cortical surface of the bovine femoral diaphyses were measured by X-ray diffraction method with characteristic Mo-Kα X-rays. However, then the residual stresses inside the cortical bone could not be accurately determined. The study here used synchrotron white X-rays obtained from the BL28B2 beam line at SPring-8 and was able to measure the residual stresses in the bovine femoral diaphysis in depth. The measurement positions in the diaphysis specimen were at 1 mm intervals from the outer surface to the inner surface of the specimen in four parts of the diaphysis: anterior, posterior, lateral, and medial. The results showed that the residual stresses in the bone axial direction at the outer cortical surface were tensile and the stresses in the inner positions of the cortical bone were compressive. In the anterior part, the residual stress at the surface was 24.7 MPa. From 2 mm to 10 mm depths inside the diaphysis, compressive residual stresses were measured and the average of these stresses was -9.0 MPa.
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  • 6 巻 (2011) 4 号 p. 270-285
    Numerical Study on the Morphology and Mechanical Role of Healthy and Osteoporotic Vertebral Trabecular Bone
    Yuto YOSHIWARA, Miguel CLANCHE, Khairul Salleh BASARUDDIN, Naoki TAKANO, Takayoshi NAKANO
    This study presents a numerical methodology to clarify the morphology of complex trabecular network architecture in human lumbar vertebra by means of the new post-processing technique for calculated microscopic stress by the homogenization method. Micro-CT image-based modeling technique is used and careful but intuitive and easy-to-use method for microstructure model, in other words region of interest (ROI), is also presented. The macroscopic homogenized properties that include not only the Young's moduli but also shear moduli could explain the difference of morphology between healthy and osteoporotic bones. This paper focuses on the change of degree of anisotropy. Then, the microscopic stress under three basis load cases was analyzed. In this analysis, the homogenization method has a merit in the computational cost. The trabeculae are classified into eight groups from the viewpoint of load bearing function against three loading conditions in the proposed post-processing of numerical results. It contributes to the understanding of the mechanical role of trabecular bone in vertebra. The primary trabecular bone that has been supposed to support the self-weight and secondary bone that connects the primary bone are successfully visualized. The discussion on the mechanical role of plate-like trabecular bone in the load path network system is also highlighted.
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  • 6 巻 (2011) 2 号 p. 64-78
    Effect of Bileaflet Valve Orientation on the 3D Flow Dynamics in the Sinus of Valsalva
    Takanobu YAGI, William YANG, Mitsuo UMEZU
    Three-dimensional (3D) evolutional behavior of flow dynamics in the aortic sinus of Valsalva was studied in vitro for finding the effects of bileaflet valve orientations in an effort to investigate possible linkages between the sinus flow and coronary circulation. A realistic model of the aortic sinus was machined inside an acrylic block. A St. Jude Medical bileaflet aortic valve was utilized. Two orientations were compared; (1) a pair of hinges aligned in the direction of the non-coronary sinus of the model (N0) and (2) of the left and right sinuses (N90). A 3D scanning three-component velocity measurement, named Fluorescent Scanning Stereoscopic Particle Image Velocimetry (FS-SPIV), was developed. Measured data were validated with an aid of two-dimensional particle image velocimetry. Good agreement confirmed the capability of quantifying the 3D mean and turbulent behavior of sinus vortices. The valve orientation was found to be unable to affect the sinus vortices during peak-systole, but had a substantial impact on regurgitation during end-systole. The superior case (N0) gave a symmetric regurgitation. The regurgitant jet was directed to the non-coronary sinus. The left and right sinuses were dominated by a well-organized recirculation from a persistent forward flow. The inferior case (N90) produced an asymmetric regurgitation with a biased jet into the left or right sinuses, leading to produce unexpected turbulence near the entrance of coronary artery. Those results suggest possible linkages between the sinus flow and coronary circulation, thereby advocating the existence of an optimal orientation of bileaflet valves.
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  • 6 巻 (2011) 3 号 p. 160-172
    Comparison of Legionella Biofilm Formations at Three Different Temperatures in Liquid Flow, in Static Liquid and on Agar Plate
    Tadashi KONISHI, Akira NISHIZONO, Tetsu YAMASHIRO, Michio KOIDE
    The biofilm formation of Legionella pneumophila on glass was examined under nutrient water flow condition at 37°C, 40°C, and 42°C. The three-dimensional structures of 8-days biofilm were analyzed using confocal laser scanning microscopy. It was revealed that the properties of the biofilms were influenced significantly by temperature changes. Equivalent outer diameters of the microcolonies were 39µm at 37°C, 189µm at 40°C and 359µm at 42°C, respectively. The most interesting observation was that the microcolonies show areas of hollowing. The hollowness or emptiness is 37% at 37°C, 52% at 40°C and 74% at 42°C, respectively. The average number of bacteria per single colony was c.a. 1 x 105 at 37°C. Also, bacteria lengths were compared among the biofilms in liquid flow, those in static liquid and those on BCYE-α agar plate. In the liquid flow, the average bacteria length was 4.4µm at 37°C, 2.9µm at 40°C and 3.5µm at 42°C, respectively, while in the static liquid and on agar plate the lengths increased with the rise of temperature. Our experiments results on the biofilm formation of L. pneumophila will provide the basis for a better understanding of the sessile mode of life of L. pneumophila.
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  • 5 巻 (2010) 3 号 p. 186-207
    Mechanical Regulation of Actin Network Dynamics in Migrating Cells
    Kennedy Omondi OKEYO, Taiji ADACHI, Masaki HOJO
    Cell migration is fundamental to various physiological processes, including metastasis, wound healing and tissue development. The complex processes involved in cell migration; polymerization, adhesion, and retraction, are mediated by highly orchestrated structure-function interactions that occur within the actin cytoskeletal structure. Thus understanding how migrating cells regulate the global dynamics of their cytoskeletal components, which result from rather localized protein-protein interactions, is fundamental to elucidating the mechanisms of cell motility. The objective of this review is to explore the mechanical regulation of actin network dynamics in migrating cells, and to discuss its regulatory role in cell migration. Specifically, we examine the various mechanical forces involved in cell migration, and how they couple with biomechanical factors to spatiotemporally regulate the dynamics of the actin cytoskeleton during cell motility. Two aspects of actin network dynamics are addressed, namely, network turnover by polymerization and depolymerization, and network flow resulting from actomyosin activity. We begin by highlighting the fundamental features of actin network dynamics in migrating cells. We then examine the coupling relationship between actin network flow and traction forces, as well as the mechanism underlying the regulation of traction forces by actin network flow. Finally, we integrate the various motility processes into a mechanical pathway in order to elucidate the importance of mechanical regulation of actin network dynamics to cell migration.
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  • 5 巻 (2010) 3 号 p. 262-271
    Biomechanical Contribution of Cytoskeletal Structures to Traction Forces in Cultured Smooth Muscle Cells
    Toshiro OHASHI, Norifumi KAMEDA, Shouji NAKAMURA, Masaaki SATO
    Cellular traction forces were measured by using a microfabricated substrate, particularly exploring how cytoskeletal structures such as actin filaments and microtubules contribute to traction forces. Smooth muscle cells isolated from bovine aortas were cultured and transfected with fluorescence proteins to visualize cell microstructures and then plated on a micropatterned elastomer substrate with arrays of micropillars. Cell spreading on the substrates produced deflection of micropillars which was used for estimation of cellular traction forces, and was closely associated with organization of stress fibers of actin filaments. Traction forces varied considerably among cells, showing the order of several 10 nN. After disruption of microtubules with nocodazole, traction forces significantly increased and there was no detectable change in formation of stress fibers. To inhibit the ROCK pathway, a signaling pathway of myosin light chain phosphorylation, possibly being induced by disruption of microtubules, significantly depressed the increase in traction forces after the disruption of microtubules. This result indicates that microtubules disassembly may regulate the actomyosin-based contractile system mainly through the ROCK pathway. The present study suggests that formation of stress fibers are mainly involved in cellular traction forces and a contribution of microtubules should include not only a force balance but also rather a modulator of the actomyosin contractile system in actin stress fibers.
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  • 5 巻 (2010) 5 号 p. 485-498
    Patient-specific Morphological and Blood Flow Analysis of Pulmonary Artery in the Case of Severe Deformations of the Lung due to Pneumothorax
    Jean-Joseph CHRISTOPHE, Takuji ISHIKAWA, Noriaki MATSUKI, Yohsuke IMAI, Kei TAKASE, Marc THIRIET, Takami YAMAGUCHI
    Pneumothorax is characterized by lung collapse. Its effect on hemodynamics, especially on pulmonary arterial blood flow, remains unclear. This patient-specific study investigated the effects of lung deformation on pulmonary blood flow during acute phase and after recovery. Arterial geometry was extracted up to the fifth generation from computed tomography images in three patients and reconstructed. Different geometrical parameters (artery bores, area ratios, and between-branch angles) were computed. The shapes of the pulmonary trunk and its branches were affected strongly by pneumothorax. To clarify the effect of geometrical perturbations on blood flow, the Navier—Stokes equations for a steady laminar flow of Newtonian incompressible fluid were solved in a reconstructed domain. The change in flow structure between acute phase and recovery was associated with variations in flow rate ratio between the right and left lungs. This study shows, possibly for the first time, that from a patient-specific numerical test, pneumothorax has a considerable impact on pulmonary arterial morphology and hemodynamics.
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  • 5 巻 (2010) 5 号 p. 591-602
    Passive Dynamic Stability of a Hovering Fruit Fly: a Comparison between Linear and Nonlinear Methods
    Na GAO, Hao LIU
    Insects exhibit exquisite control of their flapping flight, capable of performing precise stability and steering maneuverability. To tackle this highly nonlinear problem we have developed two simulation-based methods to investigate the dynamic passive stability of insect flight: linear and nonlinear methods. In the linear theory, the equations of body motion are linearized and the techniques of eigenvalue and eigenvector analysis are employed to obtain the natural modes. Three natural modes are identified including an unstable oscillatory mode, a stable fast subsidence mode and a stable slow subsidence mode, which indicate that the fruit fly hovering flight is dynamic unstable. While in the nonlinear theory, the equations of 6 DoF motion are solved directly by coupling with the N-S equations. The time-varying time histories of the state variables are calculated, indicating that the state of fruit fly under disturbance conditions shows a very nonlinear transient interval initially but turns to unstable eventually. However, our results also illustrate that a fruit fly does have sufficient time to apply some active mediation to sustain a steady hovering before losing body attitudes.
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