Three-dimensional (3D) evolutional behavior of flow dynamics in the aortic sinus of Valsalva was studied in vitro for finding the effects of bileaflet valve orientations in an effort to investigate possible linkages between the sinus flow and coronary circulation. A realistic model of the aortic sinus was machined inside an acrylic block. A St. Jude Medical bileaflet aortic valve was utilized. Two orientations were compared; (1) a pair of hinges aligned in the direction of the non-coronary sinus of the model (N0) and (2) of the left and right sinuses (N90). A 3D scanning three-component velocity measurement, named Fluorescent Scanning Stereoscopic Particle Image Velocimetry (FS-SPIV), was developed. Measured data were validated with an aid of two-dimensional particle image velocimetry. Good agreement confirmed the capability of quantifying the 3D mean and turbulent behavior of sinus vortices. The valve orientation was found to be unable to affect the sinus vortices during peak-systole, but had a substantial impact on regurgitation during end-systole. The superior case (N0) gave a symmetric regurgitation. The regurgitant jet was directed to the non-coronary sinus. The left and right sinuses were dominated by a well-organized recirculation from a persistent forward flow. The inferior case (N90) produced an asymmetric regurgitation with a biased jet into the left or right sinuses, leading to produce unexpected turbulence near the entrance of coronary artery. Those results suggest possible linkages between the sinus flow and coronary circulation, thereby advocating the existence of an optimal orientation of bileaflet valves.

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Arterial stenoses consisting of atherosclerotic plaque are subject to mechanical forces under pulsatile blood flow that may cause plaque rupture, which often leads to heart attack or stroke. Arterial plaques vary in the relative quantity and spatial organization of their component parts. We developed a more realistic multi-component composition arterial stenosis model made of hydrogel. The stiffness parameter of the non-stenotic region of the model was similar to that of human coronary arteries. The soft hydrogels were used as a model of the plaque and lipid core. We used this stenosis model to evaluate plaque deformation under a pulsatile flow system that mimicked the diastolic predominant flow phenomenon. The flow rate, pressure and deformation of the stenosis model were examined. The flow rate was found to increase as the stiffness of the plaque decreased. Maximum deformation of the stenoses appeared in the upstream area and a softer plaque model lead to larger deformation. The position of the lipid core in the plaque model did not significantly affect the flow rate but was an important factor in deformation.

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Blood flow in a filter for an extracorporeal blood circuit was analyzed numerically to assess fluid mechanical quantities related to thrombogenesis. Results showed stagnant flow regions, in particular at the downstream side of the ceiling of a filter. A particle tracking along with an evaluation of a shear stress exerted on a particle demonstrated that a particle experiences a large shear stress when passing through a pore of the filter. These results suggest that a platelet would be activated when it goes though the pore and could then aggregate with other activated platelets to develop into a thrombus beneath the ceiling of a filter. Based on this hypothesis, the filter design was modified by making a protrusion on the downstream side of the filter. The protrusion design was varied in two ways in shape (sharp, blunt) and three ways in height (1/4, 1/3, 1/2 of the height of the original filter). The simulation results showed a positive contribution of the protrusion to a decrease in the stagnant flow region on the downstream side of the filter ceiling. A comparison of the stagnant volume for models between a model with blunt protrusion and the one with sharp protrusion revealed that the blunt protrusion decreased the stagnant region more than that for models with a shape one. The protrusion also contributed to decreasing the shear stress at pores of the filter. This effect was more pronounced with an increase in the height of the protrusion. These results address benefits of the protrusion in the anti-thrombogenic design of a filter for an extracorporeal blood circuit.

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Polymethylmethacrylate (PMMA) bone cement has been widely used in orthopedic surgery for fixing prostheses and stabilizing collapsed vertebral fractures. Although it is the most popular biomaterials in orthopedics, heat generation during polymerization may cause thermal injury to the surrounding cells. Bone cells exposed to the thermal injury would secret a number of biological factors, and then locally influence a balance of bone remodeling. However, thermal tolerance of bone cells is not well understood. The aim of this study was therefore to quantify in vitro thermal injury of bone-derived cells and to establish a model to predict accumulation of the cell damage. Osteocyte, osteoblast, and fibroblast cell lines were exposed to steady supraphysiological temperatures ranging 40-75°C, and change of cell mortality depending on heating time and temperature was determined by using a dye, propidium iodide. When the cells were exposed to thermal treatment, all cell lines exhibited approximately exponential increase of cell injury at the initial phase, and then gradual decline of the increasing rate as the cell mortality approached 1. This kinetics of cell injury was described well by a logistic curve with high correlation coefficient. By comparing the slope of the logistic curves and the time to reach 50% of cell mortality, it is found that thermal tolerance of osteocytes was significantly low among three cell lines. This result indicates that thermal injury of osteocytes would be induced by the heating at a temperature that is harmless to other cell types, and both necrotic and apoptotic responses of thermally injured osteocytes might stimulate osteoclastic bone resorption.

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The presence of residual stresses in bone tissue has been noted, and the authors have reported that there are residual stresses in bone tissue. The tensile residual stresses in the bone axial direction on the cortical surface of the bovine femoral diaphyses were measured by X-ray diffraction method with characteristic Mo-Kα X-rays. However, then the residual stresses inside the cortical bone could not be accurately determined. The study here used synchrotron white X-rays obtained from the BL28B2 beam line at SPring-8 and was able to measure the residual stresses in the bovine femoral diaphysis in depth. The measurement positions in the diaphysis specimen were at 1 mm intervals from the outer surface to the inner surface of the specimen in four parts of the diaphysis: anterior, posterior, lateral, and medial. The results showed that the residual stresses in the bone axial direction at the outer cortical surface were tensile and the stresses in the inner positions of the cortical bone were compressive. In the anterior part, the residual stress at the surface was 24.7 MPa. From 2 mm to 10 mm depths inside the diaphysis, compressive residual stresses were measured and the average of these stresses was -9.0 MPa.

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Polyetheretherketone (PEEK) is becoming an interesting alternative to titanium alloys and stainless steel in orthopedics. This study compares two types of PEEK fracture plates (natural and carbon reinforced) with titanium plates of the same design. Custom designed locking orthopedic plates made from titanium alloy, natural PEEK and carbon reinforced PEEK were tested mechanically in compression and by finite element (FEM) analysis. An anatomically correct, artificial human tibia bone was used as a model for polyurethane bone models in mechanical analysis and as a model for the 3D scan used in the FEM analysis. Plate dimensions were 100 mm x 20 mm x 5 mm and M5 locking screws were created from each material. Six cyclic mechanical compression tests from 0 to 1,000 N per construct were analyzed as well as 50, 100, 200, 400, 600, 800 and 1,000 N compression tests in the FEM analysis. In the mechanical analysis, carbon reinforced PEEK consistently experienced the most plate deformation. At 200 N, natural PEEK shows more deformation than the titanium alloy but switches at 1,000 N giving titanium the most deformation. The FEM analysis consistently shows natural PEEK experiences the most strain followed by reinforced PEEK and then the titanium alloy. It is shown that the custom fracture plates made from the two PEEK materials are likely too soft to be successful in long bone fractures. It is also shown that the same plates made with Ti-alloy may be too stiff to induce successful secondary fracture recovery.

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