The stress relaxation test was performed for cultured rat aortic smooth muscle cells (SMCs) to investigate the effect of actin filaments (AFs) on viscoelastic properties of the cells. Untreated cells and cells treated with cytochalasin D to disrupt their AFs were stretched by 70-85%, and their length was kept constant with a laboratory-made micro tensile tester with feed-back control to obtain their stress relaxation curve. Viscoelastic analysis with 4-parameter Maxwell model showed that the stress relaxation process of the cells could be divided into two phases with different time constants: a fast phase with a time constant in the order of minutes, and a slow phase with a time constant in the order of hours. Elastic parameters in the two phases decreased similarly by about a half with AF disruption. Viscous parameters also decreased by ∼1/3 and ∼1/4 in the fast and the slow phase, respectively, with AF disruption. No difference was observed for the relaxation time constant in the fast phase in response to AF disruption, while the time constant in the slow phase decreased significantly by about a half. Fluctuation in tension was observed in the stress relaxation curve of the untreated cells. Such fluctuation disappeared in cells treated with cytochalasin D. These results indicates that AFs have significant effects on viscosity of SMCs in the slow phase and on the fluctuation in tension, both of which may be caused by the dynamic change of AFs.
In this study, we clarified dental occlusion functions by visualizing the displacement and deformation patterns of the periodontium under dental occlusion. A digital image correlation method served as a visualization and deformation analysis method using fresh porcine periodontium specimens. Also using dried periodontium specimens, we conducted the occlusion test to characterize the differences in displacement and deformation patterns between fresh and dried specimens. Results indicated that the periodontal ligaments deform first, followed by alveolar bones. Marked differences in displacement and deformation patterns were observed between the fresh and dried periodontium specimens.
Mechanical properties of brain tissue in high strain region are indispensable for the analysis of brain damage during traffic accidents. However, accurate data on the mechanical behavior of brain tissue under impact loading condition are sparse. In this study, mechanical properties of porcine brain tissues were characterized in their cylindrical samples cored out from their surface. The samples were compressed in their axial direction at strain rates ranging from 1 to 50 s-1. Stress relaxation test was also conducted following rapid compression with a rise time of ∼30 ms to different strain levels (20-70%). Brain tissue exhibited stiffer responses under higher impact rates: initial elastic modulus was 5.7±1.6, 11.9±3.3, 23.8±10.5 kPa (mean±SD) for strain rate of 1, 10, 50 s-1, respectively. We found that stress relaxation K(t,ε) could be analysed in time and strain domains separately. The relaxation response could be expressed as the product of two mutually independent functions of time and strain as: K(t,ε)=G(t)σe(ε), where σe(ε) is an elastic response, i.e., the peak stress in response to a step input of strain ε, and G(t) is a reduced relaxation function: G(t)=0.642e-t/0.0207+0.142e-t/0.482+0.216e-t/18.9, i.e., the time-dependent stress response normalized by the peak stress. The reduced relaxation function obtained here will serve as a useful tool to predict mechanical behavior of brain tissue in compression with strain rate greater than 10 s-1.
Research on regenerative medicine and cell therapy has progressed in recent years. Numerous cultured cells are used directly in clinical settings in regenerative medicine and cell therapy. It is important to observe the proliferation of the cultured cells using a microscope. However, the removal of culture vessels from a CO2 incubator subjects the cells to stress due to environmental changes and adversely affects cell growth. Thus, we have developed a cell culture system equipped with automated observation function that allows automated observation of cell cultures without removing the cultured cells from the CO2 incubator. This system comprises an automated cell observation unit to observe the cultured cells and an automated transfer unit to transfer the culture vessels in the CO2 incubator since this environment is harsh for mechanical devices. The automated cell observation unit consists of some optical components that should be stored in a moisture-proof case to isolate them from the environment of the CO2 incubator. The automated transfer unit is verified to have sufficient durability using oil and grease that does not exhibit any effect on cell growth. This system can acquire some time-lapse images of the cell culture continuously in the CO2 incubator.
A slider-crank mechanism whose coupler curve is the approximate ellipse is designed so that a man may perform the pedaling of the elliptical motion of the foot. Because the thigh, the shank and the foot constitute the three-link chain, the system of a man and the bicycle with the slider-crank pedal mechanism is the planar seven-link mechanism with two degree freedom. The system of a man and the ordinary bicycle is the planar five-link mechanism with two degree freedom. Kinematic characteristics of these systems are analyzed with the given pattern of the pedal angle curve during a crank rotation. Then, the crank moment and the pin joint forces of these systems are calculated for given patterns of the hip moment and the knee moment during a crank rotation and the average crank moment are estimated. It makes comparative study of calculated and experiment results of the pedal force, the crank moment and physiological results of oxygen uptake and carbon dioxide output in usual crank pedaling and in slider crank pedaling.