Journal of Biomechanical Science and Engineering

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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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★Graphics of the Year 2012
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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★Paper of the Year 2011
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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★Paper of the Year 2011
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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★Paper of the Year 2011
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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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★Graphics of the Year 2011
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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★Graphics of the Year 2011
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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★Paper of the Year 2010
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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★Paper of the Year 2010
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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★Paper of the Year 2010
5 巻 (2010) 5 号 p. 499-514
Mechanical Therapeutic Effects in Osteoporotic L1-Vertebrae Evaluated by Nonlinear Patient-specific Finite Element Analysis
Daisuke TAWARA, Jiro SAKAMOTO, Hideki MURAKAMI, Norio KAWAHARA, Juhachi ODA, Katsuro TOMITA

Patient-specific nonlinear finite element analysis (FEA) is promising for evaluating the recovery of vertebral strength. Vertebral strength is closely related to inner vertebral stress distribution and is used to assess the fracture risk for individual osteoporotic patients during drug treatment. Moreover, stress distribution is affected by individual bone shape, bone density distribution and nonlinear behavior of the mechanical properties of bone. To investigate the effectiveness of FEA considering these factors for the evaluation of drug treatment effects, patient-specific nonlinear FEAs of the first lumbar vertebrae in patients undergoing a 3-year drug treatment were performed. Changes in fracture load and distribution of failure elements in the FE models at four time points (before therapy, and after 6 and 12 months and 3 years of therapy) were compared with those of average bone density. The FEAs demonstrated that failure elements decreased notably, and fracture load increased gradually by the 3-year time point, suggesting that the vertebrae were strengthened as a result of drug treatments. Furthermore, statistical tests indicated that mechanical evaluation using the nonlinear FEAs is more sensitive for evaluating drug effects on osteoporotic bone than assessments based on average bone density.
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★Graphics of the Year 2010
5 巻 (2010) 5 号 p. 565-577
Nasal Flow Simulation Using Heat and Humidity Models
Kiyoshi KUMAHATA, Futoshi MORI, Shigeru ISHIKAWA, Teruo MATSUZAWA

The nasal cavity performs several important functions for the inhaled air, such as temperature and humidity adjustments. Although it is necessary to obtain velocity, temperature, and humidity distributions during inhalation in order to understand the nasal cavity's functions, it is difficult to measure them noninvasively in the nasal cavity. Therefore, we have continued to study nasal flow simulation with heat and humidity transport. In such a simulation, the governing equations include a continuum equation and the equations describing momentum, energy, and water transport. The temperature and humidity of the inhaled air are adjusted by heat and water exchange on the nasal cavity wall's surface. Therefore, in the simulation, these roles of the wall in the energy and water transport equations were included as the boundary conditions. Although in related studies of nasal flow simulation with heat and humidity transport, the nasal cavity wall's surface temperature and humidity were constant, here they were treated as degrees of using Newton's cooling law. A flow including temperature and humidity in a realistic human nasal cavity shape was simulated. The simulation results agreed well with the measurements reported by Keck at al. Therefore, this study concludes that our model can simulate the heat and humidity exchange occurring in the nasal cavity. In addition, it was found that the temperature and humidity adjustment functions worked effectively in the front and narrow regions of the nasal cavity.
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★Graphics of the Year 2010

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