Toshio Yuhta

Reduction of polyethylene wear by concave dimples on the frictional surface in artificial hip joints

For the purpose of reduction of polyethylene wear generated in artificial hip joints, concave dimples were formed on the surface of the metal femoral head by electrical discharge etching with the constant diameter of 0.5 mm, pitch of 1.2 mm, and depth of 0.1 mm. Using a hip joint simulator, the total amount of polyethylene wear was 7.2 mg in the concave-patterned condition and 23.1 mg in the nonpatterned condition. The reasons for the reduction of polyethylene wear by the concave pattern may be i) a reduction of abrasive wear by providing escape dimples for wear particles and ii) an improvement in the lubricity on the frictional surface by the supply of lubricant that is stored in dimples.

Surface pitting of heart valve disks tested in an accelerated fatigue tester

There are various reports on the fracture of mechanical heart valves implanted in humans or animals and it has been pointed out that fractures are induced by erosion of the disk surface due to cavitation bubbles. Cavitation erosion on mechanical heart valves was studied using our originally designed accelerated fatigue tester. Several valve housings with different compliance values were used. The number and position of pits on the valve disk were measured using an optical microscope. Disk-closing velocity was measured and cavitation bubbles were monitored by a high-speed video camera. It was found that disk-closing velocity increased and cavitation erosion was enhanced with an increase in compliance of the valve holder. Therefore, careful attention should be paid to the compliance of an accelerated fatigue tester.

Lymphocyte activation effect of (1→6)-2, 5-anhydro-d-glucitol and it derivatives with 3,4-di-O-methyl and sulfate groups

(1-->6)-2,5-Anhydro-3,4-di-O-methyl-D-glucitol (2a) and (1-->6)-2,5-anhydro-D-glucitol (2c) and its sulfated derivative (2d) were synthesized and their biological activities were evaluated in regards to the effects on murine lymphocytes. The polymers showed different effects on the lymphocytes depending on the substituent groups. The sulfated polymer (2d) induced mitogenic activities, and specifically activated the CD4(-)CD8(-) subset of lymphocytes.

Numerical study of flow dynamics through prosthetic heart valves in a steady state flow model.

In this paper a numerical technique and simulation models are described to analyze flow patterns around prosthetic heart valves under steady flow conditions. The finite difference method was employed to solve the time-dependent and non-linear Navier-Stokes equations (NS eq.) for an incompressible viscous fluid. Chorins scheme was used to solve the governing equations, NS eq. and equation of continuity. In this method the discretized algebraic equations approximating the governing differential equations were obtained from the analytic solutions of the governing equations ; this method was shown capable for providing a stable numerical solution and a proper simulation of the flow dynamics. The flow geometry, including a flow chamber and a prosthetic heart valve, was overlaid with a rectangular grid. The several types of clinical valves and the trial model valves developed in our laboratory were chosen as subjects of this study.