Estimation of wall strength of the aortic aneurysms is necessary for the prediction of their rupture risk. We previously found a significant correlation between their tensile strength σ_MAX and a yielding parameter τ_σ, which is the stress when tangent elastic modulus reaches at 63% of the plateau level. This may indicate that the wall strength is estimated from their pressure-diameter relationship. Here we show a possible mechanism of the correlation between τ_σ and σ_MAX by focusing on alignment of collagen fibers. Thin (150-µm) slices of porcine thoracic aortas were uniaxially stretched in circumferential direction until failure under a microscope, and a retardance, a phase shift when polarized light passes through a birefringent material, was measured as the degree of collagen fiber alignment. Strength σ_MAX correlated significantly with τ_σ as obtained previously. The retardance increased with the increase in the stress and reached a plateau at the stress σ_Ret-plateau, indicating that σ_Ret-plateau is the stress at which most of the intramural collagen fibers have aligned. The stress σ_Ret-plateau correlated significantly with τ_σ and both parameters has similar values. This may indicate that the aortic wall yields when all of collagen fibers become straight. Smaller σ_Ret-plateau means that most collagen fibers are stretched and loaded at smaller stress, resulting in failure at smaller stress. This seems to be a reason for the significant correlation between τ_σ and σ_MAX.

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There is a demand for three-dimensional (3D) angiogenesis model including endothelial cells (ECs) and mesenchymal stem cells (MSCs), which are known to differentiate into pericytes, to construct stabilized and matured microvascular networks in vitro. However, it remains to be elucidated how MSCs affected on ECs in the process of 3D angiogenesis. In this study, we utilized a microfluidic device to develop a 3D coculture system including human umbilical vein ECs and human MSCs, which allowed us to investigate the effects of MSCs on ECs in the context of 3D angiogenesis. A series of EC:MSC ratio was tested in the EC-MSC coculture. First, we confirmed that MSCs differentiated into pericytes by direct EC-MSC contacts. Next, we found that MSCs attenuated vascular sprout formation of ECs regardless of EC:MSC ratio in the early stage of 3D angiogenesis as well as extension of microvascular networks in the later stage. ECs and MSCs were also cultured under interstitial flow to enhance angiogenesis. However, the stabilization effects of MSCs on the extension of capillary structures were dominant over the promotion effects of the interstitial flow. These results indicate the stabilization effect of MSCs on the formation of microvascular networks in vitro. Although some HMSCs differentiated into pericytes and located around microvascular networks, vascular structures became thick over time in coculture. The 3D EC-MSC coculture model described in this study is useful to further investigate culture microenvironments for constructing stabilized and matured microvascular networks with aligning pericytes.

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In this study, we report measurements of the adhesion force of a cell sheet made by applying the ninety-degree peel test. The ninety-degree peel test has been applied to general sheet materials and its procedure is defined by the International Standard Organization (ISO). Only a few studies have been able to measure adhesion force of fragile cell sheets because the sheets are easily broken and cannot be fixed to the conventional fixtures of test systems. Additionally, there are no ninety-degree peel test systems which can measure weak forces such as adhesion force of cell sheets. Therefore, we developed a new fixture to hold the sheet in place during measurements of the adhesion force and we also developed a special test system. Our novel fixture is a multi hook type fixture which allows cell sheets to be fixed to the test system without breaking. We successfully measured adhesion force of a cell sheet.

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Chitosan nonwoven mesh conduit was introduced with perforating pores on the wall by laser-drilling process. The pore size was set at 200 µm and the pore interval at 1mm. Twelve mm long grafts of following 4 groups (N=5, respectively) were implanted to rat sciatic nerve defects: non-pore, 2 lines of pores, 4 lines of pores and isograft. After 12 weeks standard nerve function evaluations were performed including functional test, electro conductivity test and histological analysis. It was found that revascularization of the conduit contents was improved with pores drilled, but accompanied nerve regenerative improvements were only shown as maturation of fasciculi, not with the general parameters of axon diameter and density.

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The objective of this study was to conduct the musculoskeletal simulation and the EMG (Electromyogram) measurement for the same trial of the same swimmer performing the breaststroke, and to compare the simulated and measured results, in order to discuss the validity of the musculoskeletal simulator for swimming, which was developed in the previous study. In the experiment, two subject swimmers swam in a circulating tank. The swimming motions were captured by two cameras for the underwater motion and two other cameras for the motion above the water. The EMG were simultaneously measured for eight muscles: triceps brachii, biceps brachii, pectoralis major, latissimus dorsi, deltoid, rectus femoris, biceps femoris, and tibialis anterior. The measured swimming motions were used as the inputs in the simulation. As a result of the comparison between the simulation and experiment, it was found that the performance of the simulation was satisfactory. The simulation could estimate the peak timing as well as the curve shape of the actual muscle activity except for the excessive activation and the biarticular muscle. In addition, the differences in muscle activity due to the subject found in the experiment were sufficiently reproduced by the simulation.

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This research formulates an optimal control model that reproduces human sitting movements on a chair (stand-to-sit movements). The model switches its dynamics from a three-link and three-joint structure to a one-link and one-joint one at the time (switching time) when its thigh-link touches the seat of a chair, and optimizes its criterion function composed of three kinds of energy costs, a center-of-gravity cost, and an input cost. The research clarifies the model's performance in reproducing human stand-to-sit movements and discusses factors indispensable for sitting on a chair. Consequently, the following results are derived: (1) the model can produce various kinds of stand-to-sit movements by adjusting the switching time primarily and one of the input weights secondarily; (2) the energy costs and the center-of-gravity cost hardly affect the model's performance; (3) there exists the optimal switching time for the criterion function to take a minimum, and the stand-to-sit movements predicted using the optimal switching time agree well with the measured ones. These results suggest that the proposed model can be a plausible and effective model of the human stand-to-sit movement mechanism and that the switching time is a primary factor involved strongly in human sitting movements on a chair and the input weights can be secondary factors.

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This paper addresses the question of what is the feasible range of movement for a body to remain balanced while standing. A feasible region in the center of mass position-velocity plane has been proposed previously. This paper shows that for a certain individual with given anatomical and mechanical characteristics, the feasible movements of the CoM, or more generally the range of states at which the control of balance would be possible, can be analytically found through a mechanical reasoning. This paper introduces a subspace of the motion state space, namely the integrated stable subspaces (ISS), and proves that the control of balance is possible all over the ISS. In order to illustrate how the method may be used in practice, the feasible region for a well-known one-DoF mechanical model as well as for a two-DoF one is found using this approach, and is compared to that found by the conventional method. The feasible region found by this method depends on the physical properties of a body including anatomical parameters of a body as well as the torque (control input) constraints. The method works with any arbitrary shape of the input constraint.

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