Journal of Biomechanical Science and Engineering
Online ISSN : 1880-9863
ISSN-L : 1880-9863
Volume 3, Issue 1
Displaying 1-5 of 5 articles from this issue
  • Shufeng LI, Hiroshi IZUI, Michiharu OKANO, Taku WATANABE
    2008 Volume 3 Issue 1 Pages 1-12
    Published: 2008
    Released on J-STAGE: January 08, 2008
    The sintering behaviors and resulting properties of hydroxyapatite (HA) were studied by employing Spark plasma sintering (SPS) process. An As-received HA powder was sintered and the sintering pressure was set as 22.3MPa, 44.6MPa and 66.9MPa respectively. At each pressure, the HA powder was sintered at different temperatures ranging from 800°C to 1000°C with a duration time of 8 minutes. The results showed that HA compact was rapidly densified to near theoretical density with the relative density of 99.1%. The samples sintered at 44.6MPa possess higher flexural strength and Young's modulus than those at 22.3MPa. The flexural strength and Young's modulus achieved a maximum value of 123.2MPa and 75.2GPa respectively when the samples were sintered at 950°C and at pressure of 44.6MPa. The external pressure accelerates the densification behaviors and overlade external pressure at 66.9MPa resulted in high residual stresses and thus deteriorated the mechanical properties. The XRD results indicated there was no decomposition of HA sintered at elevated temperature up to 1000°C. The drop of mechanical properties was considered as the result of grain growth and hence residual stress induced microcracks.
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  • Takanobu FUKUNAGA, Kosaku KURATA, Junpei MATSUDA, Hidehiko HIGAKI
    2008 Volume 3 Issue 1 Pages 13-24
    Published: 2008
    Released on J-STAGE: February 04, 2008
    Osteocytes inside bone matrix play an important role in detecting the local mechanical environment. In order to study their mechanical responses, we have developed a mechanical loading device that can apply physiological and supraphysiological strains to osteocytes embedded in a three dimensional (3-D) gel. The newly designed elastic chamber with ten separated culture wells can simultaneously apply five different strain magnitudes for the mechanical stretching of the cells. When the gel-embedded MLO-Y4 cells were prepared in the wells, they were subjected to mechanical stretching of physiological and supraphysiological strain levels for 24 h. The cell viability assay indicated that significant dead cells were observed for strain values greater than 8890 με. Beyond this threshold, the number of dead cells linearly increased with the strain magnitude. The supernatant of MLO-Y4 cells, which was exposed to strain levels beyond the threshold, showed a significant increase in tartrate-resistant acid phosphatase (TRACP) activity in the bone marrow culture. These experimental findings indicate that the local death of osteocytes provides an important mechanism to initiate bone resorption.
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  • Hiromichi NAKADATE, Yasunori HIROSE, Eiichi SEKIZUKA, Haruyuki MINAMIT ...
    2008 Volume 3 Issue 1 Pages 25-37
    Published: 2008
    Released on J-STAGE: February 19, 2008
    The magnitude of pressure and shear stress varies according to anatomical locations and species. It is of the utmost importance that the in vivo condition of these stresses is taken into account in in vitro experiments. In this study, we developed a new in vitro pulsatile perfusion system that is able to mimic pressures and shear stresses with accuracy and over a wide physiological range. Our system is composed of a hydraulic model of a systemic circulation. Pressure and flow rate (i.e., shear stress) were independently controlled by two resistance tubes, and pulse amplitude was controlled by air volume in a compliance tube. The resistance value of two resistance tubes and air volume in a compliance tube were calculated by system simulation. Then we recreated the pressure and shear stress of in vivo measurement data using our system. Results showed mean pressure and mean shear stress at aorta level (100 mmHg and 1.20 Pa), small artery level (80 mmHg and 1.86 Pa), arteriole level (60 mmHg and 1.41 Pa), capillary level (30 mmHg and 0.70 Pa), venule level (20 mmHg and 0.28 Pa), and vena cava level (10 mmHg and 0.15 Pa) to be recreated. We also exposed cultured human aortic endothelial cells (HAEC) to physiological pulsatile flow, which was similar to that in the human aorta at pressure 80/120 mmHg and shear stress 1.0/1.5 Pa. In the results, HAEC was elongated and oriented in the flow direction.
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  • Ken-ichi KONNO, Tadashi KOSAWADA, Hiroshi YAMAZAKI, Yasukazu HOZUMI, K ...
    2008 Volume 3 Issue 1 Pages 38-49
    Published: 2008
    Released on J-STAGE: March 07, 2008
    In this study, a new three-dimensional micro vibration stage is developed, in which a doubly steric L-shaped clamped-free beam type vibrator is utilized. The developed three-dimensional micro vibration stage, which has very simple structure and is quite easily sterilized, is extended to control system of cell culture. Focusing on osteoblast character which is sensitive to external mechanical stimuli, a normal human osteoblast is chosen as a test subject. Dynamic stimulation is applied to the normal human osteoblast utilizing the developed three-dimensional vibration stage. In order to estimate effect of dynamic stimulation upon cultured cell, we define parameters of projected area and slenderness ratio of the cultured normal human osteoblast. Statically cultured cells of 4th and 6th passage were provided for experiments. It was observed that the projected area of normal human osteoblast increased, while the slenderness ratio decreased according to the number of cell passage increasing. Shape of the 6th passage of dynamically stimulated cells was not similar to that of same passage of control, but to that of 4th passage of control. From the viewpoint of morphology, the present study has shown the significant effect of dynamic stimulation upon cultured cells.
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  • Nan ZHANG, Ryojun IKEURA, Yuanxin WANG, Kazuki MIZUTANI, Hideki SAWAI
    2008 Volume 3 Issue 1 Pages 50-61
    Published: 2008
    Released on J-STAGE: March 11, 2008
    In this study, we considered a single rotational degree-of-freedom experimental system, in addition to a mass-spring-damper-friction biomechanical model of the human arm, and then investigated master-slave and master-semi-master cooperative motions. For the master-slave cooperative motion, we developed a mass-spring-friction biomechanical model for the slave's arm. Within the investigated range, we found the damping factor to be zero, and the stiffness and dynamic friction to be individually constant. We also determined the torque characteristics in the master-slave and master-semi-master cooperative motions. In the master-slave cooperative motion, although the master subject had to overcome the entire impedance resistance of the slave subject's arm, the master found it easier to slow down and stop the motion. In master-semi-master cooperative motion, when the semi-master subject switched from passive arm movement to active arm movement, the stiffness characteristics disappeared and constant torque characteristics were observed. At that moment, the master subject felt it took less effort to perform active arm movement. As a result, we assume that in human-robot cooperative tasks, during accelerating motion, we can apply the characteristics of the semi-master to a robot through torque control, and during deceleration (braking) motion, we can apply the slave characteristics to a robot by means of impedance control.
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