We hypothesized that flow stagnation might precipitate aneurysm rupture. We considered that aspect ratio (AR; dome/neck ratio) might be better geometric index to determine intraaneurysmal flow and to predict the tendency to rupture. Fundamental pattern of intraaneurysmal flow was composed of in-flow, circulation flow, and out-flow. Intraaneurysmal flow became dramatically slow when AR changed from low ratio to high ratio. When AR was higher than 1.6, secondary circulation flow occurred at the dome side of the aneurysm.
The AR has gained the attention of interventional radiologist because a low ratio is generally associated with greater technical difficulty and poorer results from coil embolization of the aneurysms. To predict the angiographic outcome of coil embolization, we evaluated angiographic findings after the initial treatment of 94 aneurysms of 88 patients and follow-up angiography. We statistically analyzed the relationships between aneurysm size, volume embolization ratio, AR and arterial geometry and results on follow-up angiography. Among these factors the difference in AR was significant (p<0.05) between the complete occlusion group and incomplete occlusion group and aneurysms with an AR larger than 2.0 showed a high success ratio. AR is considered one of most useful indices predicting successful coil embolization for intracranial aneurysm.

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We have systematically studied the surface sliding friction of hydrogels, and various unique features in gel friction have been discovered. The frictional force and its dependencies on the load are quite different depending on the chemical structures of the gels, surface properties of the opposing substrates, and the measurement condition, which are completely different from those of solids. Most importantly, the friction coefficient of gels exhibits a value as low as 0.001, which cannot be obtained from the friction between two solid materials.
Recently, we developed a general method to synthesize hydrogels with extremely low friction by introducing linear polymer brush on the surface of gels. Then, the frictional coefficient became μ=10^-4.
However, conventional gels are mechanically too weak to be used as loading bearing materials. We recently developed anomalously strong gels by introducing a double network structure of the gel. These high strength hydrogels, containing 90 % water, sustain a compressive pressure as high as decades of MPa and show a high wear resistance due to their low friction. These gels might open new era of soft and wet materials for substituting articular cartilage and other tissues.

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