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.

Keywords

Insect Flight, Fruit Fly, Passive Dynamic Stability, Flight Dynamics, NS Equation

Paper information

Na GAO and Hao LIU, “Passive Dynamic Stability of a Hovering Fruit Fly: a Comparison between Linear and Nonlinear Methods”, Journal of Biomechanical Science and Engineering, Vol. 5, No. 5 (2010), pp.591-602 . doi:10.1299/jbse.5.591

The preparation of an implant site using a surgical drill is a common procedure in orthopedic surgery, such as for the internal fixation of fractures. An increase in temperature during such a procedure results in the potential for thermal invasion of the bone, which may delay healing or reduce the stability of the fixation. Therefore, minimizing invasion during bone drilling is important to ensure the stability of the implant, and this requires surgical drills with an optimal design. This study investigated the optimal design of surgical drills by comparing the drilling characteristics (i.e., the cutting force and temperature increase) using the Taguchi fractional factorial method. The control factors (helix angle, web thickness, point angle, and the levels of these three parameters) were placed in an L₉ orthogonal array and drilling tests were conducted with nine experimental drills based on the array. The results show that the optimal levels of the three design factors of the surgical drill and their percentage contribution depend on the drilling characteristics. However, confirmation tests indicated that the design optimization did not greatly affect the performance improvement and its results showed poor reproducibility. This is possibly because the various cutting conditions encountered in actual clinical situations were not adequately considered.

Keywords

Surgical Drill, Drill Design, Drilling Bone, Internal Fixation, Taguchi Method

Paper information

Tadamaru UEDA, Atsushi WADA, Ken-ichi HASEGAWA, Yasuyuki ENDO, Yoshihiro TAKIKAWA, Takanori HASEGAWA and Toshiaki HARA, “Design Optimization of Surgical Drills Using the Taguchi Method”, Journal of Biomechanical Science and Engineering, Vol. 5, No. 5 (2010), pp.603-614 . doi:10.1299/jbse.5.603

Background. Ultrasound evaluation of articular cartilage is not accurate if the ultrasound probe is not perpendicular to the cartilage surface. However a probe angle adjustment is difficult because of the manual procedure and the lack of angle index for the measurer. The aim of this study is to propose "Rise-to-Peak time" as an index of probe angle and to evaluate its effectiveness in evaluating articular cartilage surfaces.
Methods. The "Rise-to-Peak time" is defined as the time interval between the rise of the first peak (50% amplitude of the first peak) and the first positive peak following the minimum peak of the echo. The relationship between the Rise-to-Peak time and probe angle was evaluated using several reflection surfaces including that of articular cartilage.
Findings. The "Rise-to-Peak time" increased monotonically with increases in the angle between the probe and the reflection surface, and showed good agreement with calculated values for small angle changes (<3 degrees).
Interpretation. The "Rise-to-Peak time" provides an index of probe angle in the ultrasound measurement of articular cartilage. Availability of echo-amplitude correction using the "Rise-to-Peak time" is evaluated.

Keywords

Ultrasound, Cartilage, Evaluation, Measurement Support

Paper information

Keisuke YAMADA, Kohei ODA and Naohide TOMITA, “Measurement of Probe Angle for Ultrasound Evaluation of Articular Cartilage Using “Rise-to-Peak Time””, Journal of Biomechanical Science and Engineering, Vol. 5, No. 5 (2010), pp.615-624 . doi:10.1299/jbse.5.615

In order to investigate vascular diseases such as cause of atherosclerosis and myocardial infarction, relationships of endothelial cells (ECs) covered with surface blood vessels and blood flow stimulation have been experimentally studied. In the study, in order to investigate the relationship between response of ECs and shear stress caused by blood flow, a non-intrusive measurement method for shear stress distribution and topography of living ECs with subcellular resolution was developed based on velocity distributions measured by micro PIV (Particle Image Velocimetry) technique. ECs were cultured with higher shear stress stimulation in a straight microchannel with width of 400 µm and depth of 100 µm made from polydimethylsiloxane (PDMS) microchip. By optimizing cells cultured condition such as the liquid introduction method and the surface coating for enhancement of cell attachment on the microchannel wall, a cell culture method in the microchip with continuous shear stress stimulation was developed. Height and wall shear stress distributions of ECs cultured with shear stresses of 0.1 and 1.0 Pa were measured. The developed technique is useful to study relationships between wall shear stress distribution and transient morphological response in the living cells.

Keywords

Endothelial Cell, Shear Stress, Morphology, Microchannel, Micro PIV

Paper information

Yasuhiko SUGII, “Simultaneous Measurement of Wall Shear Stress Distribution and Three-Dimensional Shape of Living Endothelial Cells Cultured in Microchannel”, Journal of Biomechanical Science and Engineering, Vol. 5, No. 5 (2010), pp.625-634 . doi:10.1299/jbse.5.625

Cyclic mechanical loading can stimulate bone cells in vivo, resulting in the mechano-adaptive osteogenic response of bone. The objective of this study was to investigate the capability of mechanical loading to promote three-dimensional osteoblastic calcification in vitro. A bone-like construct was made by seeding osteoblasts that were obtained from mesenchymal stem cells of rat bone marrow into a type I collagen sponge scaffold. A sinusoidal compressive mechanical load with a peak of 0.2% deformation was applied to the construct at 0.8 Hz for 3 min per day for 35 consecutive days using a piezoelectric mechanical stimulator. This mechanical loading applies not only substrate strain, but also oscillatory fluid flow strain to the cells in the sponge. The degree of osteoblastic calcification was monitored non-destructively once a day utilizing a near-infrared light. The degree of calcification was evaluated as bulk density or calcium content (mg/cm³) based on the optical data. In constructs stimulated by mechanical loading, the degree of calcification started to increase after day 10 and ultimately reached a bulk density of about 44 mg/cm³ and a calcium content of about 4 mg/cm³. In contrast, controls without stimulation did not display a noticeable increase in calcification. Microscopic observation of cross-sectioned samples revealed a heterogeneous distribution of calcification, where a rich calcified matrix was observed in the upper region of the construct, which also had a higher cell density. In conclusion, mechanical loading could enhance osteogenesis in vitro, suggesting its applicability to bone tissue engineering.

Keywords

Osteogenesis, Osteoblast, Mechanical Stimulation, In Vitro, Bone, Tissue Engineering

Paper information

Shigeo M. TANAKA, “Mechanical Loading Promotes Calcification of Tissue-Engineered Bone In Vitro”, Journal of Biomechanical Science and Engineering, Vol. 5, No. 5 (2010), pp.635-645 . doi:10.1299/jbse.5.635