Keywords

Paper information

Ryuhei YAMAGUCHI and Susumu KUDO, “Preface”, Journal of Biomechanical Science and Engineering, Vol. 3, No. 2 (2008), pp.62-62 . doi:10.1299/jbse.3.62

Cell Nuclei play a critical role in controlling gene expression and replicating DNA, and is known to deform in association with cell shape changes in response to external forces. This study dealed with morphological analysis to quantitatively assess the effect of three different mechanical stimuli including fluid shear stress, cyclic stretching, and hydrostatic pressure on nucleus morphology. Fluorescence images showed that fluid shear stress and cyclic stretching induced cell elongation and orientation very specifically to the direction of flow and stretch, respectively. In contrast, hydrostatic pressure induced cell elongation at non-preferred orientation. The nuclei were also found to deform in the same manner as that of the cells, which was, in particular, dependent on the type of mechanical stimuli, possibly suggesting the direct mechanical linkages between cell surface receptors, cytoskeletal meshworks, and nuclei. It was also shown that cytoskeletal meshworks may contribute to pre-existing strain of the nuclei.

Keywords

Endothelial Cells, Nucleus Remodeling, Shear Stress, Cyclic Stretching, Hydrostatic Pressure, Cytoskeletal Meshworks

Paper information

Toshiro OHASHI, Kazuhiko HANAMURA, Daisaku AZUMA, Naoya SAKAMOTO and Masaaki SATO, “Remodeling of Endothelial Cell Nucleus Exposed to Three Different Mechanical Stimuli”, Journal of Biomechanical Science and Engineering, Vol. 3, No. 2 (2008), pp.63-74 . doi:10.1299/jbse.3.63

High-grade stenoses can limit blood flow and produce conditions in which an artery may collapse. The resultant compression may be important in the development of atherosclerotic plaque fracture and subsequent thrombosis or distal embolization. We have developed stenosis models made of polyvinyl alcohol hydrogel, which closely approximate an arterial disease situation, and performed pulsatile flow experiments. Valsalva's maneuver and cough cause a sharp increase in jugular venous pressure to greater than 50 mmHg. Such transient pressure increases within the carotid sheath may augment the external pressure around the carotid artery. We applied external pressure to a stenosis model in two different forms and discussed the influences of external pressure on pulsatile flow and deformation in the stenosis model.

Keywords

Atherosclerosis, Stenosis, Plaque, Pulsatile Flow, Biomechanics

Paper information

Jie JI, Shunichi KOBAYASHI, Hirohisa MORIKAWA, Dalin TANG and David N. KU, “Influences of External Pressure on Flow and Deformation in Arterial Stenosis Model”, Journal of Biomechanical Science and Engineering, Vol. 3, No. 2 (2008), pp.75-84 . doi:10.1299/jbse.3.75

For the simulation of the fluid-structure interaction (FSI) between the blood flow and blood vessel walls, we have examined the voxel-based FSI method. This method uses a Cartesian grid, called voxel, made from medical images. Further, we have tested the accuracy and reliability of this simple method and have observed its features. In this document, we discuss the background, kinetic models of the blood vessel, a numerical method, and the result of an experiment conducted using an artificial identical shape and an actual realistic shape.

Keywords

Blood Vessel, Cartesian Grid, Voxel, Medical Image, Fluid Structure Interaction

Paper information

Kiyoshi KUMAHATA, Masahiro WATANABE and Teruo MATSUZAWA, “Blood Flow Simulation System with Interaction between Blood Flow and Blood Vessel Wall using Image Based Cartesian Grid”, Journal of Biomechanical Science and Engineering, Vol. 3, No. 2 (2008), pp.85-100 . doi:10.1299/jbse.3.85

Many studies have been carried out on the relationship between the occurrence and progression of circulatory diseases and hemodynamics. However, it is difficult to obtain accurate and detailed information on blood flow in the living body with existing experimental and numerical methods. The authors have previously proposed the Ultrasonic-Measurement-Integrated (UMI) simulation and shown that the blood flow in an aortic aneurysm can be accurately reproduced when feedback signals derived from the difference between measured and computed Doppler velocities are fed back to the numerical simulation. In the present study, we performed a fundamental numerical experiment in which UMI simulation was applied to a developed laminar pipe flow using an axisymmetric model in order to understand the effect of the feedback law on the accuracy of UMI simulation systematically. The effect of two types of ultrasonic probes, the linear scanning type and the sector scanning type, and the effect of 70° and 110° irradiating angles of the ultrasonic beam in the linear probe were investigated. It was confirmed that the result of UMI simulation asymptotically approached the standard solution of developed laminar flow downstream of the feedback domain in all cases using the linear probe and the sector probe with axisymmetric feedback. Under the present conditions, a linear probe with a radiation angle of 70° was most effective, whereas there was not so much improvement in the accuracy in the case using the sector probe. The effect of the singularity of the axisymmetric coordinate on the pipe axis was observed in the axial velocity profile near the entrance of the feedback domain, but disappeared some distance downstream in that domain.

Keywords

Measurement Integrated Simulation, Computational Fluid Dynamics, Ultrasonic Measurement, Blood Flow, Color Doppler Imaging, Boundary Condition

Paper information

Lei LIU, Kenichi FUNAMOTO and Toshiyuki HAYASE, “Numerical Experiment for Ultrasonic-Measurement-Integrated Simulation of Developed Laminar Pipe Flow Using Axisymmetric Model”, Journal of Biomechanical Science and Engineering, Vol. 3, No. 2 (2008), pp.101-115 . doi:10.1299/jbse.3.101

It is well known that endothelial cells (ECs) respond to the fluid imposed shear stress and change their shapes and functions. We have focused on the importance of cytoplasmic micro-mechanical strain in mechano-sensing mechanism of ECs. To this end, the cytosolic Ca2+ responses of ECs to the mechanical stimulus by laser tweezers that can apply the micro-mechanical force to nano/micro-organisms without any physical contact, were investigated. When the laser spot focused on the nucleus of EC was slightly moved, the cytosolic Ca2+ increased immediately in the same EC, whereas there was no Ca2+ increase without laser spot movement. In the absence of extracellular Ca2+ in the medium or the blockade of stretch activated ion channels, there was also an increase of Ca2+ in stimulated ECs. Therefore, the increased Ca2+ in stimulated ECs is considered to be derived from intracellular Ca2+ store. The heterogeneous Ca2+ propagation from the stimulated EC to surrounding ECs was also observed. Two types of Ca2+ wave propagation were observed, the fast one that the velocity was more than 20 μm/sec, and the slow one that the velocity was less than 1 μm/sec. The micro-stress induced by the micro-movement of the nucleus can be a trigger of the cytosolic Ca2+ increase and the cytoplasmic micro-mechanical strain may play an important role in mechano-sensing mechanism of ECs.

Keywords

Endothelial Cells, Mechano-Transduction, Calcium Ion, Laser Tweezers

Paper information

Noriyuki KATAOKA, Ken HASHIMOTO, Susumu KUDO, Ryuhei YAMAGUCHI, Katsuhiko TSUJIOKA and Fumihiko KAJIYA, “Intracellular Ca2+ Responses in Cultured Endothelial Cells to Mechanical Stimulation by Laser Tweezers”, Journal of Biomechanical Science and Engineering, Vol. 3, No. 2 (2008), pp.116-123 . doi:10.1299/jbse.3.116