Yasuhito Yamamoto

Oblique Alignment of Stress Fibers in Cells Reduces the Mechanical Stress in Cyclically Deforming Fields

The stress fiber (bundles of actin filaments) is one of the most prominent cytoskeletal components that contributes to the maintenance of cell architecture. It has generally been believed that upon cyclic stretching, both cells and their stress fibers become perpendicularly aligned to the direction of stretching. However, using our newly developed stretching device, we have recently found the contrary evidence that stress fibers in endothelial cells rapidly become rearranged at a specific oblique angle relative to the direction of stretching [Takemasa, T., K. Sugimoto, K. Yamashita: Exp. Cell Res. 230, 407-410 (1997)]. In light of this finding, we attempted to establish the explanation for such a phenomenon. First, we investigated the effects of possible modulators on the angle of the stress fibers; those were, modification of the stretching program, dependency of extracellular matrix types, and their reproducibility in other cell species. However, it seemed that the orientation was solely depending on the stretching amplitude applied. Next, we analyzed alterations in stress fiber length during loading tests using two kinds of deforming experiment systems. It was thus revealed that stress fibers aligned at a particular angle so as to minimize their length alterations in cyclic deforming fields. Rearrangement of the stress fibers at this angle probably occurs as a result of avoiding compressive stress and may be interpreted as a way of reducing the mechanical stress to which they are subjected during the deformation. This hypothesis well explains the reason not only for the survival of the stress fibers at a particular oblique angle, but also for the reduced numbers of stress fibers found at the other angles on cyclic deforming fields.

Computational mechanical model studies on the spontaneous emergent morphogenesis of the cultured endothelial cells

To address questions concerning why and how the morphology of endothelial cells (ECs) forms under shear stress loading, a computational fluid dynamics (CFD) three-dimensional (3D) model of ECs simulating cell shape was designed. A full 3D non-linear CFD simulation was conducted to estimate the wall shear stress (WSS) distribution. The model cell was capable of random rotation, deformation, migration, and proliferation. Flow was computed after each update of the cell shape with infinitesimal configuration changes. After a finite interval of the flow computation, only the infinitesimal configuration changes that reduced the WSS were allowed to accumulate. As a result of the very long free-run computation experiment, starting with a sub-confluent pattern of cells, the model cells became confluent and were elongated and aligned, with a shape index (SI) very close to that reported for cells in vivo. The average WSS converged to the lowest value at the same time.

The hyper hospital-virtual reality based medical system on the computer network-its concept and user-configurable virtual world creating system

We have been developing a novel medical care system which is constructed on an electronic or computerized information network using virtual reality as the principal human interface. The major purpose of the hyper hospital is to restore humane interactions between patients and various medical caretakers by making a much closer contact between them in the real medical scene than that in current conventional medical practice. In the present study, we discuss the most fundamental part of the development of the virtual reality system for the medical use, that is, system software for the creation of the virtual world which can be defined and modified by users of various levels, not only by the medical caretakers, but particularly by patients.

Evaluation of the safety features of a virtual reality system

Publisher Summary This chapter discusses the evaluation of the safety features of a virtual reality (VR) system. Several measures of the physiological, biochemical, neurological, and psychological fatigue are calculated before, during, and after the control experiments. Similar is the case with the VR loading experiments in the study discussed in the chapter. It is found that there is subjective fatigue, particularly related with the psychological condition. The urinary catecholamine release (including epinephrine and dopamine) is found to increase in the VR loading sessions as well as the control video sessions. No increase in the norepinephrine release in the VR experiments are found while it increased in the control video session. Based on this, it is speculated that the use of VR does not have much effect on the physical condition, but may slightly affect the mental or psychological state; however, the extent of this effect is not as severe as the usual video presentation.