The hemodynamics of blood flow in the Circle of Willis (CoW) is considered to be important for the understanding of disease progression in cerebral circulation. In this research, we developed a method by combining 1D-0D model with the medical imaging data of magnetic resonance imaging (MRI) and single photon emission computed tomography (SPECT), in order to investigate the hemodynamics in CoW. The MRI data was used as the arterial geometry parameter for 1D model. The SPECT data was used as the reference data for the flow rates at the efferent arteries of CoW, which indicated if adjustment needed to be made to the peripheral cerebral resistance for 0D model. We applied our method to two patients and compared the simulation results with PC-MRI measurement data. The comparison showed the differences of flow distribution in the afferent arteries between simulation results and measurement data were 0.6–6.0% and 5.7–13.2% respectively in two cases. Both simulations captured the individual difference of flow distribution in the CoW. The results suggested that our method can be used to obtain the hemodynamics information in the CoW for an individual patient.

It is important to quantitatively evaluate the flow behaviour of complex fluids such as paste-like foods. In this study, we investigated the flow properties of a paste-like food model using a weak-gel model. As a model of paste- like food, agar microgel suspensions were prepared using a water-in-oil (W/O) emulsion system. Because the microgels prepared by this method have a spherical shape, their flow properties can be evaluated quantitatively. The steady state viscosity and dynamic modulus of the suspensions were measured with the volume fraction of the microgel particles ranging from 0.68 to 0.80. Because the flow curves showed a pseudo-plastic flow, they were analysed using the Herschel-Bulkley equation to obtain characteristic flow parameters, namely, the viscosity coefficient (k), apparent yield stress (σ_y), and the Herschel-Bulkley index (n). The frequency dependence of the complex modulus was analysed using the weak-gel model to obtain two parameters, namely the coordination number (z), which relates to the relaxation behaviour, and gel strength (A_f). A sudden increase in both σ_y and z was observed when the volume fraction was close to 0.77. Moreover, k and A_f were also found to undergo a sudden increase at the same volume fraction. This value is expected to be the critical volume fraction at which the microgel particles reach a random close packing state. The results showed that we can make quantitative evaluation of the flow behaviour of a complex fluid under a small deformation by using the weak-gel model.

UV-crosslinked gelatin nanogel was prepared without using chemical crosslinking agents and its thermoresponsive behaviors were investigated. The particle size of the nanogels decreased on heating, which is attributed to the helix-to-coil transition of gelatin. On the other hand, the increase in the particle size on cooling was not observed in the quiescent solutions, but was noticeably accelerated by the application of shear stress.

We have developed a microporous covered stent (MCS) for the treatment of intracranial aneurysms (IAs). MCS promotes intentional thrombosis in the IA by blood stagnation and facilitates IA embolization treatment by clotting of whole blood in the IA. Flow reduction is a key property of such stent-type IA embolization devices. In this study, we evaluated the flow reduction property of MCS, and compered that of a general balloon expandable stent (bare stent, BS) for supporting a stenotic vessel and a typical flow diverter stent (FD) for IA treatment. This was carried out using particle imaging velocimetry (PIV) and an in vitro flow simulator with a saccular IA and straight parent vessel model. The PIV results show that the area mean shear rates in the IA flow were reduced to 34.7% (5.56 s^–1) for the BS model, 9.2% (1.48 s^–1) for the FD model, and 2.7% (0.43 s^–1) for the MCS model with respect to the unstented condition (16.04 s^–1) at a Reynolds number of 600. Considering that the flow reduction property of the MCS model is three times higher than that of the FD model, it is clear that the MCS facilitates more reliable IA embolization than FD.