Language：English   Publishing type：Research paper (scientific journal)   Publisher：AIP Publishing  

Purification of blood from microparticles while maintaining its suitability for autotransfusion provides a revolutionary support for advanced healthcare through circulatory system of blood flows. However, there is a great challenge in the separation of particles from blood physically with high efficiency. Here, we proved a novel approach for whole blood treatment of microparticle separation utilizing a three-dimensional microfluidic chip with helical structures of tubular channels. The chips with helical structures characterized by spiral diameters and pitches are fabricated with flexible silicon-based tubes with different inner diameters in which photolithography is not required. By controlling Reynolds and Dean numbers to generate appropriate stable Dean flow along the tubular channels, microparticles with diameters from 15 to 30 μm are separated directly from untreated whole blood with about 10% blood loss, and the free-hemoglobin concentration after separation remains in a safe level for further clinical transfusion. Two distinct patterns of particle accumulation in the cross section of microtubes are observed. It is also interesting to find that different from many practices that lyse red blood cells before particle or cell sorting, the intensive cell-particle interactions in whole blood facilitate particle focusing to regions closer to channel walls than in pure liquid without red blood cells. This label-free particle separation method, based on hydrodynamical interactions among the particles and deformable blood cells in stable Dean vortexes of helical tubular microfluidic chips, not only paves the way for innovative healthcare using functional microparticles but also enlightens the sorting of nucleated cells separation from whole blood biophysically.

DOI： 10.1063/5.0266385

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Idiopathic normal-pressure hydrocephalus (Hakim's disease) is characterized by ventricular enlargement and disproportionately enlarged subarachnoid space hydrocephalus, leading to localized brain deformation. Differentiating regional brain volume changes in Hakim's disease from those in Alzheimer's disease, Hakim's disease with Alzheimer's disease, and mild cognitive impairment provides insights into disease-specific mechanisms. This study aimed to identify disease-specific patterns of brain volume changes in Hakim's disease, Alzheimer's disease, Hakim's disease with Alzheimer's disease, and mild cognitive impairment and compare them with those in cognitively healthy individuals using an advanced artificial intelligence-based brain segmentation tool. The study included 970 participants, comprising 52 patients with Hakim's disease, 256 with Alzheimer's disease, 25 with Hakim's disease with Alzheimer's disease, 163 with mild cognitive impairment, and 474 healthy controls. The intracranial spaces were segmented into 100 brain and 7 CSF subregions from 3D T1-weighted MRIs using brain subregion analysis. The volume ratios of these regions were compared among the groups using Glass's Δ, referencing 400 healthy controls aged ≥50 years. Hakim's disease exhibited significant volume reduction in the supramarginal gyrus of the parietal lobe and the paracentral gyrus of the frontal lobe. Alzheimer's disease exhibited prominent volume loss in the hippocampus and temporal lobe, particularly in the entorhinal cortex, fusiform gyrus, and inferior temporal gyrus. Hakim's disease with Alzheimer's disease showed significant volume reductions in the supramarginal gyrus of the parietal lobe, similar to Hakim's disease, whereas temporal lobe volumes were relatively preserved compared with those in Alzheimer's disease. Patients with mild cognitive impairment aged ≥70 years had comparable regional brain volume ratios with healthy controls in the same age group. The Hakim's disease and Hakim's disease with Alzheimer's disease groups were characterized by volume reductions in the frontal and parietal lobes caused by disproportionately enlarged subarachnoid space hydrocephalus-related compression compared with temporal lobe atrophy observed in the Alzheimer's disease group. These disease-specific morphological changes highlight the need for longitudinal studies to clarify the causes of compression and atrophy.

DOI： 10.1093/braincomms/fcaf122

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Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.jcp.2025.113945

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1093/radadv/umae027

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Language：English   Publishing type：Research paper (scientific journal)  

BACKGROUND: Bidirectional reciprocal motion of cerebrospinal fluid (CSF) was quantified using four-dimensional (4D) flow magnetic resonance imaging (MRI) and intravoxel incoherent motion (IVIM) MRI. To estimate various CSF motions in the entire intracranial region, we attempted to integrate the flow parameters calculated using the two MRI sequences. To elucidate how CSF dynamics deteriorate in Hakim's disease, an age-dependent chronic hydrocephalus, flow parameters were estimated from the two MRI sequences to assess CSF motion in the entire intracranial region. METHODS: This study included 127 healthy volunteers aged ≥ 20 years and 44 patients with Hakim's disease. On 4D flow MRI for measuring CSF motion, velocity encoding was set at 5 cm/s. For the IVIM MRI analysis, the diffusion-weighted sequence was set at six b-values (i.e., 0, 50, 100, 250, 500, and 1000 s/mm2), and the biexponential IVIM fitting method was adapted. The relationships between the fraction of incoherent perfusion (f) on IVIM MRI and 4D flow MRI parameters including velocity amplitude (VA), absolute maximum velocity, stroke volume, net flow volume, and reverse flow rate were comprehensively evaluated in seven locations in the ventricles and subarachnoid spaces. Furthermore, we developed a new parameter for fluid oscillation, the Fluid Oscillation Index (FOI), by integrating these two measurements. In addition, we investigated the relationship between the measurements and indices specific to Hakim's disease and the FOIs in the entire intracranial space. RESULTS: The VA on 4D flow MRI was significantly associated with the mean f-values on IVIM MRI. Therefore, we estimated VA that could not be directly measured on 4D flow MRI from the mean f-values on IVIM MRI in the intracranial CSF space, using the following formula; e0.2(f-85) + 0.25. To quantify fluid oscillation using one integrated parameter with weighting, FOI was calculated as VA × 10 + f × 0.02. In addition, the FOIs at the left foramen of Luschka had the strongest correlations with the Evans index (Pearson's correlation coefficient: 0.78). The other indices related with Hakim's disease were significantly associated with the FOIs at the cerebral aqueduct and bilateral foramina of Luschka. FOI at the cerebral aqueduct was also elevated in healthy controls aged ≥ 60 years. CONCLUSIONS: We estimated pulsatile CSF movements in the entire intracranial CSF space in healthy individuals and patients with Hakim's disease using FOI integrating VA from 4D flow MRI and f-values from IVIM MRI. FOI is useful for quantifying the CSF oscillation.

DOI： 10.1186/s12987-024-00552-6

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Cellular traction forces are contractile forces that depend on the material/substrate stiffness and play essential roles in sensing mechanical environments and regulating cell morphology and function. Traction forces are primarily generated by the actin cytoskeleton and transmitted to the substrate through focal adhesions. The cell nucleus is also believed to be involved in the regulation of this type of force; however, the role of the nucleus in cellular traction forces remains unclear. In this study, we explored the effects of nucleus-actin filament coupling on cellular traction forces in human dermal fibroblasts cultured on substrates with varying stiffness (5, 15, and 48 kPa). To investigate these effects, we transfected the cells with a dominant-negative Klarsicht/ANC-1/Syne homology (DN-KASH) protein that was designed to displace endogenous linker proteins and disrupt nucleus-actin cytoskeleton connections. The force that exists between the cytoskeleton and the nucleus (nuclear tension) was also evaluated with a fluorescence resonance energy transfer (FRET)-based tension sensor. We observed a biphasic change in cellular traction forces with a peak at 15 kPa, regardless of DN-KASH expression, that was inversely correlated with the nuclear tension. In addition, the relative magnitude and distribution of traction forces in nontreated wild-type cells were similar across different stiffness conditions, while DN-KASH-transfected cells exhibited a different distribution pattern that was impacted by the substrate stiffness. These results suggest that the nucleus-actin filament coupling play a homeostatic role by maintaining the relative magnitude of cellular traction forces in fibroblasts under different stiffness conditions.

DOI： 10.1007/s10237-024-01839-1

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BACKGROUND: Disproportionately enlarged subarachnoid-space hydrocephalus (DESH) is a key feature for Hakim disease (idiopathic normal pressure hydrocephalus: iNPH), but subjectively evaluated. To develop automatic quantitative assessment of DESH with automatic segmentation using combined deep learning models. METHODS: This study included 180 participants (42 Hakim patients, 138 healthy volunteers; 78 males, 102 females). Overall, 159 three-dimensional (3D) T1-weighted and 180 T2-weighted MRIs were included. As a semantic segmentation, 3D MRIs were automatically segmented in the total ventricles, total subarachnoid space (SAS), high-convexity SAS, and Sylvian fissure and basal cistern on the 3D U-Net model. As an image classification, DESH, ventricular dilatation (VD), tightened sulci in the high convexities (THC), and Sylvian fissure dilatation (SFD) were automatically assessed on the multimodal convolutional neural network (CNN) model. For both deep learning models, 110 T1- and 130 T2-weighted MRIs were used for training, 30 T1- and 30 T2-weighted MRIs for internal validation, and the remaining 19 T1- and 20 T2-weighted MRIs for external validation. Dice score was calculated as (overlapping area) × 2/total area. RESULTS: Automatic region extraction from 3D T1- and T2-weighted MRI was accurate for the total ventricles (mean Dice scores: 0.85 and 0.83), Sylvian fissure and basal cistern (0.70 and 0.69), and high-convexity SAS (0.68 and 0.60), respectively. Automatic determination of DESH, VD, THC, and SFD from the segmented regions on the multimodal CNN model was sufficiently reliable; all of the mean softmax probability scores were exceeded by 0.95. All of the areas under the receiver-operating characteristic curves of the DESH, Venthi, and Sylhi indexes calculated by the segmented regions for detecting DESH were exceeded by 0.97. CONCLUSION: Using 3D U-Net and a multimodal CNN, DESH was automatically detected with automatically segmented regions from 3D MRIs. Our developed diagnostic support tool can improve the precision of Hakim disease (iNPH) diagnosis.

DOI： 10.3389/fnagi.2024.1362637

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We investigated the reduction in regional brain volume and cerebral blood flow (CBF) with aging and explored potential sex differences in healthy brains. Three-dimensional (3D) T1-weighted magnetic resonance imaging (MRI), time-of-flight magnetic resonance angiography, and four-dimensional (4D) flow MRI were performed on 129 healthy volunteers aged 22-92 years. The brains of healthy volunteers were segmented into 21 subregions using 3D T1-weighted MRI and CBFs in 16 major intracranial arteries were measured using 4D flow MRI. The cortical gray matter volume decreased linearly with aging, whereas the cerebral white matter volume increased until the 40s and then decreased, and the subcortical gray matter volume changed little with aging. The cortical gray matter volume was significantly associated with the total CBF of the major intracranial arteries distal to the circle of Willis; however, the cerebral white matter and subcortical gray matter volumes were not. Generally, women have higher total CBF than men, particularly in their 40s and younger, despite the smaller intracranial volume and smaller diameters of intracranial arteries than men. This may contribute to the higher incidence of subarachnoid hemorrhage due to cerebral aneurysms and migraine in women.

DOI： 10.1177/00368504241266371

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How do regional brain volume ratios and cerebral blood flow (CBF, mL/min) change with aging, and are there sex differences? This study aimed to comprehensively evaluate the relationships between regional brain volume ratios and CBF in healthy brains. The study participants were healthy volunteers who underwent three-dimensional T1-weighted MRI, time-of-flight MR angiography, and four-dimensional (4D) flow MRI between 2020 and 2022. The brain was automatically segmented into 21 brain subregions from 3D T1-weighted MRI, and CBF in 16 major intracranial arteries were measured by 4D flow MRI. The relationships between segmented brain volume ratios and CBFs around the circle of Willis were comprehensively investigated in each decade and sex. This study included 129 healthy volunteers (mean age ± SD, 48.2 ± 16.8; range, 22-92 years; 43 males and 86 females). The association was strongest between the cortical gray matter volume ratio and total outflow of the intracranial major arteries distal to the circle of Willis (Pearson's correlation coefficient, r: 0.425). In addition, the mean flow of the total inflow and outflow around the circle of Willis were significantly greater in women than men, and significant left-right differences were observed in CBFs even on the peripheral side of the circle of Willis. Moreover, the correlation was strongest between the left cortical gray matter volume ratio and the combined flows of the left anterior and posterior cerebral arteries distal to the circle of Willis (r: 0.486). There was a trend toward greater total intracranial CBF, especially among women in their 40s and younger, who had a larger cortical gray matter volume. This finding may be one of the reasons for the approximately twofold higher incidence of cerebral aneurysms and subarachnoid hemorrhage, and a threefold higher incidence of migraine headaches.

DOI： 10.14336/AD.2023.1122

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The cerebral arterial network covering the brain cortex has multiscale anastomosis structures with sparse intermediate anastomoses (O[102] μm in diameter) and dense pial networks (O[101] μm in diameter). Recent studies indicate that collateral blood supply by cerebral arterial anastomoses has an essential role in the prognosis of acute ischemic stroke caused by large vessel occlusion. However, the physiological importance of these multiscale morphological properties-and especially of intermediate anastomoses-is poorly understood because of innate structural complexities. In this study, a computational model of multiscale anastomoses in whole-brain-scale cerebral arterial networks was developed and used to evaluate collateral blood supply by anastomoses during middle cerebral artery occlusion. Morphologically validated cerebral arterial networks were constructed by combining medical imaging data and mathematical modeling. Sparse intermediate anastomoses were assigned between adjacent main arterial branches; the pial arterial network was modeled as a dense network structure. Blood flow distributions in the arterial network during middle cerebral artery occlusion simulations were computed. Collateral blood supply by intermediate anastomoses increased sharply with increasing numbers of anastomoses and provided one-order-higher flow recoveries to the occluded region (15%-30%) compared with simulations using a pial network only, even with a small number of intermediate anastomoses (≤10). These findings demonstrate the importance of sparse intermediate anastomoses, which are generally considered redundant structures in cerebral infarction, and provide insights into the physiological significance of the multiscale properties of arterial anastomoses.

DOI： 10.1371/journal.pcbi.1011452

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Cerebrospinal fluid (CSF) dynamics has dramatically changed in this century. In the latest concept of CSF dynamics, CSF is thought to be produced mainly from interstitial fluid (ISF) excreted from the brain parenchyma and is absorbed in the meningeal lymphatics. Moreover, CSF does not always flow from the ventricles to the subarachnoid space unidirectionally through the foramina of Magendie and Luschka. In an environment of increased intracranial CSF in idiopathic normal pressure hydrocephalus (iNPH), CSF freely moves through the inferior choroidal point of the choroidal fissure, which interfaces between the inferior horn of the lateral ventricles and the ambient cistern, and through the velum interpositum between the third ventricle and the quadrigeminal cistern. The structure of the hippocampus adjacent to the inferior part of the choroidal fissure may be important in preventing the accumulation of waste products in the hippocampus. A recent imaging technology for CSF dynamics, such as four-dimensional flow and intravoxel incoherent motion (IVIM) MRI, can visualize and quantify the pulsatile complex CSF motion in clinical usage. We present the current concepts of CSF dynamics with advanced MRI techniques, which will be helpful in the management and understanding of the pathogenesis of chronic hydrocephalus in adults.

DOI： 10.1016/j.wneu.2023.07.110

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OBJECTIVE: The presence of tightened sulci in the high-convexities (THC) is a key morphological feature for the diagnosis of idiopathic normal pressure hydrocephalus (iNPH), but the exact localization of THC has yet to be defined. The purpose of this study was to define THC and compare its volume, percentage, and index between iNPH patients and healthy controls. METHODS: According to the THC definition, the high-convexity part of the subarachnoid space was segmented and measured the volume and percentage from the 3D T1- and T2-weighted MRIs in 43 patients with iNPH and 138 healthy controls. RESULTS: THC was defined as a decrease in the high-convexity part of the subarachnoid space located above the body of the lateral ventricles, with anterior end on the coronal plane perpendicular to the anterior commissure-posterior commissure (AC-PC) line passing through the front edge of the genu of corpus callosum, the posterior end in the bilateral posterior parts of the callosomarginal sulci, and the lateral end at 3 cm from the midline on the coronal plane perpendicular to the AC-PC line passing through the midpoint between AC and PC. Compared to the volume and volume percentage, the high-convexity part of the subarachnoid space volume per ventricular volume ratio (HCVR) <0.6 was the most detectable index of THC on both 3D T1- and T2-weighted MRIs. CONCLUSIONS: To improve the diagnostic accuracy of iNPH, the definition of THC was clarified, and HCVR <0.6 proposed as the best index for THC detection in this study.

DOI： 10.1016/j.wneu.2023.05.077

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OBJECTIVES: To verify the reliability of the volumes automatically segmented using a new artificial intelligence (AI)-based application and evaluate changes in the brain and CSF volume with healthy aging. METHODS: The intracranial spaces were automatically segmented in the 21 brain subregions and 5 CSF subregions using the AI-based application on the 3D T1-weighted images in healthy volunteers aged > 20 years. Additionally, the automatically segmented volumes of the total ventricles and subarachnoid spaces were compared with the manually segmented volumes of those extracted from 3D T2-weighted images using the intra-class correlation and Bland-Altman analysis. RESULTS: In this study, 133 healthy volunteers aged 21-92 years were included. The mean intra-class correlations between the automatically and manually segmented volumes of the total ventricles and subarachnoid spaces were 0.986 and 0.882, respectively. The increase in the CSF volume was estimated to be approximately 30 mL (2%) per decade from 265 mL (18.7%) in the 20s to 488 mL (33.7%) in ages above 80 years; however, the increase in the volume of total ventricles was approximately 20 mL (< 2%) until the 60s and increased in ages above 60 years. CONCLUSIONS: This study confirmed the reliability of the CSF volumes using the AI-based auto-segmentation application. The intracranial CSF volume increased linearly because of the brain volume reduction with aging; however, the ventricular volume did not change until the age of 60 years and above and then gradually increased. This finding could help elucidate the pathogenesis of chronic hydrocephalus in adults. KEY POINTS: • The brain and CSF spaces were automatically segmented using an artificial intelligence-based application. • The total subarachnoid spaces increased linearly with aging, whereas the total ventricle volume was around 20 mL (< 2%) until the 60s and increased in ages above 60 years. • The cortical gray matter gradually decreases with aging, whereas the subcortical gray matter maintains its volume, and the cerebral white matter increases slightly until the 40s and begins to decrease from the 50s.

DOI： 10.1007/s00330-023-09632-x

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BACKGROUND: In the cerebrospinal fluid (CSF) dynamics, the pulsations of cerebral arteries and brain is considered the main driving force for the reciprocating bidirectional CSF movements. However, measuring these complex CSF movements on conventional flow-related MRI methods is difficult. We tried to visualize and quantify the CSF motion by using intravoxel incoherent motion (IVIM) MRI with low multi-b diffusion-weighted imaging. METHODS: Diffusion-weighted sequence with six b values (0, 50, 100, 250, 500, and 1000 s/mm2) was performed on 132 healthy volunteers aged ≥ 20 years and 36 patients with idiopathic normal pressure hydrocephalus (iNPH). The healthy volunteers were divided into three age groups (< 40, 40 to < 60, and ≥ 60 years). In the IVIM analysis, the bi-exponential IVIM fitting method using the Levenberg-Marquardt algorithm was adapted. The average, maximum, and minimum values of ADC, D, D*, and fraction of incoherent perfusion (f) calculated by IVIM were quantitatively measured in 45 regions of interests in the whole ventricles and subarachnoid spaces. RESULTS: Compared with healthy controls aged ≥ 60 years, the iNPH group had significantly lower mean f values in all the parts of the lateral and 3rd ventricles, whereas significantly higher mean f value in the bilateral foramina of Luschka. In the bilateral Sylvian fossa, which contain the middle cerebral bifurcation, the mean f values increased gradually with increasing age, whereas those were significantly lower in the iNPH group. In the 45 regions of interests, the f values in the bilateral foramina of Luschka were the most positively correlated with the ventricular size and indices specific to iNPH, whereas that in the anterior part of the 3rd ventricle was the most negatively correlated with the ventricular size and indices specific to iNPH. Other parameters of ADC, D, and D* were not significantly different between the two groups in any locations. CONCLUSIONS: The f value on IVIM MRI is useful for evaluating small pulsatile complex motion of CSF throughout the intracranial CSF spaces. Patients with iNPH had significantly lower mean f values in the whole lateral ventricles and 3rd ventricles and significantly higher mean f value in the bilateral foramina of Luschka, compared with healthy controls aged ≥ 60 years.

DOI： 10.1186/s12987-023-00415-6

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The equilibrium positions of red blood cells(RBCs) and their steady motions in microchannel affect the hemodynamics in vivo and microfluidic applications in cellular-scale. However, the dynamic behavior of a single RBC in three-dimensional cylindrical microchannels still needs to be classified systematically. Here, with an immersed boundary method, the phase diagrams of the profiles and positions of RBCs under equilibrium states are illustrated in a wide range of Capillary numbers. The effects of initial positions are explored as well. Numerical results present that the profiles of RBCs at equilibrium states transform from snaking, tumbling to slipper or parachute with the increase of flow rates, and whether RBCs finally approaches slipper or parachute motion under large shear rates is dependent on their initial positions. With the increase of tube diameters, the equilibrium positions of RBCs are closer to tube walls relatively. Although both the increase of membrane shear modulus and the viscosity ratio are regarded as the stiffening of RBCs, the change of membrane property does not affect the dependence of the profiles and positions of RBCs at equilibrium states on the shear rates of the flow obviously, but with the increase of viscosity ratio RBCs move furtherly away from the centerline of the tube associating with more asymmetric characteristics in their stable profiles. The present results not only contribute for better understanding the dynamic behavior and multiple profiles of single RBC in microcirculation, but also provide fundamentals in a large range of Capillary numbers for cell sorting with microfluidic devices.

DOI： 10.1063/5.0141811

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Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Mechanical Engineers  

DOI： 10.1299/mej.22-00204

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Publishing type：Research paper (scientific journal)   Publisher：AIP Publishing  

The membrane tensions of suspended nucleated cells moving in blood flows in capillary networks are quite different from those of spreading cells, a fact that is crucial to many pathological processes, such as the metastasis of cancers via circulating tumor cells (CTCs). However, a few studies have examined membrane tensions in suspended cells, especially when interacting with other cells of different stiffnesses in low-Reynolds number flows at the cellular level. Taking CTCs as an example, we use the immersed boundary method to analyze the relationship between membrane tensions and their motional behaviors under the influence of fluid–cell–vessel interactions. The effects of vessel diameter and hematocrit on the shear tension and average isotropic tension are also analyzed. The results suggest that the confinement of the vessel wall determines membrane tensions on CTCs until the ratio of the vessel diameter to cell size becomes slightly larger than unity, at which point cell–cell interactions become the crucial factor. The increase in interactions between red blood cells and CTCs with the increase in the hematocrit in larger vessels promotes membrane tensions not only through the migration of CTCs to the vessel wall but also through a reduction in the translational motion and rotation of CTCs. The present study provides support rooted in biofluid mechanics for mechanobiological research on the metastasis and apoptosis of CTCs in microvessels.

DOI： 10.1063/5.0080488

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Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Mechanical Engineers  

DOI： 10.1299/jbse.22-00014

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Wiley  

Cell nuclei behave as viscoelastic materials. Dynamic regulation of the viscoelastic properties of nuclei in living cells is crucial for diverse biological and biophysical processes, specifically for intranuclear mesoscale viscoelasticity, through modulation of the efficiency of force propagation to the nucleoplasm and gene expression patterns. However, how the intranuclear mesoscale viscoelasticity of stem cells changes with differentiation is unclear and so is its biological significance. Here, we quantified the changes in intranuclear mesoscale viscoelasticity during osteoblastic differentiation of human mesenchymal stem cells. This analysis revealed that the intranuclear region is a viscoelastic solid, probably with a higher efficiency of force transmission that results in high sensitivity to mechanical signals in the early stages of osteoblastic differentiation. The intranuclear region was noted to alter to a viscoelastic liquid with a lower efficiency, which is responsible for the robustness of gene expression toward terminal differentiation. Additionally, evaluation of changes in the mesoscale viscoelasticity due to chromatin decondensation and correlation between the mesoscale viscoelasticity and local DNA density suggested that size of gap and flexibility of chromatin meshwork structures, which are modulated depending on chromatin condensation state, determine mesoscale viscoelasticity, with various rates of contribution in different differentiation stages. Given that chromatin within the nucleus condenses into heterochromatin as stem cells adopt a specific lineage by restricting transcription, viscoelasticity is perhaps a key factor in cooperative regulation of the nuclear mechanosensitivity and gene expression pattern for stem cell differentiation.

DOI： 10.1096/fj.202100536rr

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Other Link： https://onlinelibrary.wiley.com/doi/full-xml/10.1096/fj.202100536RR

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Royal Society  

Thrombi form a micro-scale fibrin network consisting of an interlinked structure of nanoscale protofibrils, resulting in haemostasis. It is theorized that the mechanical effect of the fibrin clot is caused by the polymeric protofibrils between crosslinks, or to their dynamics on a nanoscale order. Despite a number of studies, however, it is still unknown, how the nanoscale protofibril dynamics affect the formation of the macro-scale fibrin clot and thus its mechanical properties. A mesoscopic framework would be useful to tackle this multi-scale problem, but it has not yet been established. We thus propose a minimal mesoscopic model for protofibrils based on Brownian dynamics, and performed numerical simulations of protofibril aggregation. We also performed stretch tests of polymeric protofibrils to quantify the elasticity of fibrin clots. Our model results successfully captured the conformational properties of aggregated protofibrils, e.g., strain-hardening response. Furthermore, the results suggest that the bending stiffness of individual protofibrils increases to resist extension.

DOI： 10.1098/rsif.2021.0554

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Other Link： https://royalsocietypublishing.org/doi/full-xml/10.1098/rsif.2021.0554

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Despite numerous experimental observations regarding heart failure with preserved ejection fraction (HFpEF), which is characterized mainly by left ventricular hypertrophy and a left ventricular ejection fraction over 50%, myocardial dynamics under HFpEF have not yet been fully clarified, particularly regarding the relationship between myocardial strain distribution and myocardial work. To address this issue, we numerically investigated radial distribution of myocardial strain during a cardiac cycle with fixed internal volume at the end of the systolic and diastolic phases under different mechanical conditions, such as those involving myocardial thickness and elasticity of myocardial fibers. The myocardium was a modeled as a visco-hyperelastic continuous material. This model was taken into account that active contractile stress along the myocardial fiber direction depends on membrane potential change. Our numerical results showed that both radial and circumferential strains decreased as wall thickness increased, which reflected cardiac hypertrophy, but that myocardial work became larger than that observed with thin ventricular walls. Further, the change in left ventricular diastolic internal pressure caused circumferential strain, while fiber stiffness contributed to radial strain. Since peak circumferential strain was well estimated by the maximum difference between total internal and myocardial volumes, measuring the epicardial contraction rate should be helpful in understanding patients with HFpEF.

DOI： 10.1007/s10439-020-02706-7

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

The cerebral vasculature has a complex and hierarchical network, ranging from vessels of a few millimeters to superficial cortical vessels with diameters of a few hundred micrometers, and to the microvasculature (arteriole/venule) and capillary beds in the cortex. In standard imaging techniques, it is difficult to segment all vessels in the network, especially in the case of the human brain. This study proposes a hybrid modeling approach that determines these networks by explicitly segmenting the large vessels from medical images and employing a novel vascular generation algorithm. The framework enables vasculatures to be generated at coarse and fine scales for individual arteries and veins with vascular subregions, following the personalized anatomy of the brain and macroscale vasculatures. In this study, the vascular structures of superficial cortical (pial) vessels before they penetrate the cortex are modeled as a mesoscale vasculature. The validity of the present approach is demonstrated through comparisons with partially observed data from existing measurements of the vessel distributions on the brain surface, pathway fractal features, and vascular territories of the major cerebral arteries. Additionally, this validation provides some biological insights: (i) vascular pathways may form to ensure a reasonable supply of blood to the local surface area; (ii) fractal features of vascular pathways are not sensitive to overall and local brain geometries; and (iii) whole pathways connecting the upstream and downstream entire-scale cerebral circulation are highly dependent on the local curvature of the cerebral sulci.

DOI： 10.1371/journal.pcbi.1007943

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DOI： 10.1016/j.jcp.2018.08.002

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DOI： 10.1007/s11517-018-1928-7

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Society of Mechanical Engineers (ASME)  

DOI： 10.1115/1.4039150

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

This paper presents a novel data assimilation method for patient-specific blood flow analysis based on feedback control theory called the physically consistent feedback control-based data assimilation (PFC-DA) method. In the PFC-DA method, the signal, which is the residual error term of the velocity when comparing the numerical and reference measurement data, is cast as a source term in a Poisson equation for the scalar potential field that induces flow in a closed system. The pressure values at the inlet and outlet boundaries are recursively calculated by this scalar potential field. Hence, the flow field is physically consistent because it is driven by the calculated inlet and outlet pressures, without any artificial body forces. As compared with existing variational approaches, although this PFC-DA method does not guarantee the optimal solution, only one additional Poisson equation for the scalar potential field is required, providing a remarkable improvement for such a small additional computational cost at every iteration. Through numerical examples for 2D and 3D exact flow fields, with both noise-free and noisy reference data as well as a blood flow analysis on a cerebral aneurysm using actual patient data, the robustness and accuracy of this approach is shown. Moreover, the feasibility of a patient-specific practical blood flow analysis is demonstrated.

DOI： 10.1002/cnm.2910

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.clinbiomech.2018.01.001

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.jbiomech.2017.09.008

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DOI： 10.1007/s11517-017-1617-y

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DOI： 10.1007/s11517-016-1541-6

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.jbiomech.2016.11.033

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DOI： 10.1678/rheology.45.243

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Language：Japanese   Publisher：Japan Soc. of Med. Electronics and Biol. Engineering  

DOI： 10.11239/jsmbe.54.28

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DOI： 10.1299/jbse.15-00555

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Mechanical Engineers  

DOI： 10.1299/jbse.14-00246

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DOI： 10.1002/fld.3968

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DOI： 10.1016/j.jcp.2014.08.011

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.jcp.2013.11.034

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DOI： 10.1016/j.apm.2012.10.050

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.4208/cicp.141210.110811s

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DOI： 10.3811/jjmf.26.60

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.jcp.2011.11.038

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Authorship：Lead author,　Corresponding author   Language：English   Publisher：The Japan Society of Mechanical Engineers  

DOI： 10.1299/jbse.7.72

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Language：English   Publisher：The Japan Society of Mechanical Engineers  

DOI： 10.1299/jbse.7.84

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DOI： 10.1115/1.4005184

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DOI： 10.11345/nctam.59.245

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DOI： 10.1016/j.jcp.2011.06.012

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DOI： 10.1016/j.jcp.2010.09.032

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/fld.2460

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

Fluid flows interacting with deformable wavy channel are simulated by a newly developed full-Eulerian simulation method. A single set of the governing equations for fluid and solid is employed, and a volume-of-fluid (VOF) function is used for describing the multi-component geometry. The stress field is defined by volume-averaging the stresses of the individual components through VOF. The temporal change in the solid deformation is described on the Eulerian frame by updating a left Cauchy-Green deformation tensor. The SMAC method is employed, and a second-order Adams-Bashforth and Crank-Nicolson methods are applied for time-updating the momentum equation. The spatial derivatives are discretized by the second-order central difference, except for the advections of the VOF and the left Cauchy-Green tensor (fifth-order WENO scheme). The full-Eulerian fluid-structure coupling method is applied to a pressure-driven elastic wavy channel of sinusoidal wall geometry to study the interaction between a fluid and elastic object. The elastic walls oscillate as it interacts with the fluid, and the transient phenomenon to steady state is simulated. With a neo-Hookean viscoelastic model as a constitutive law, the obtained numerical results of the elastic wall deformations (for different moduli of elasticity) show good agreements with the theoretical prediction employing the lubrication and steady Stokes approximations. Also, under some pulsating pressure conditions, a nonlinear behavior of the flow rate is studied by varying the amplitude of the pressure difference.

DOI： 10.1299/jfst.5.475

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DOI： 10.1016/j.jcp.2010.02.023

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DOI： 10.1007/s00466-010-0484-2

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DOI： 10.1016/j.jcp.2009.11.008

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DOI： 10.1016/j.jcp.2009.02.009

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Language：Japanese   Publisher：The Japan Society for Industrial and Applied Mathematics  

This paper presents a class of finite volume methods of high accuracy based on the CIP/Multi-Moment concept. The resulting numerical formulations work well for both structured and unstructured meshes and appear to be attractive in computational efficieny and robustness. Numerical tests will be reported as well.

DOI： 10.11540/bjsiam.18.2_95

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Publishing type：Research paper (scientific journal)  

DOI： 10.1002/fld.1616

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DOI： 10.1016/j.jcp.2006.08.015

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DOI： 10.1016/j.jcp.2005.08.002

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DOI： 10.1016/j.cpc.2005.07.003

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Total pages：vii, 226p   Language：Japanese  

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Language：English   Publisher：Pleiades Publishing  

DOI： 10.1007/978-981-10-7542-1_31

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DOI： 10.1016/j.piutam.2017.03.022

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DOI： 10.7133/jca.16-90005

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DOI： 10.1109/BIBE.2016.22

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DOI： 10.1109/BIBE.2016.32

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Language：English   Publisher：Kluwer Academic Publishers  

DOI： 10.1007/978-94-007-7769-9_3

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DOI： 10.1007/978-3-319-02913-9_87

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DOI： 10.1016/j.piutam.2014.01.018

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DOI： 10.1007/978-3-319-02913-9_183

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DOI： 10.11345/japannctam.62.0.67.0

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DOI： 10.11345/japannctam.61.0.82.0

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DOI： 10.11345/japannctam.61.0.84.0

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DOI： 10.1115/AJK2011-04001

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Abstract An interaction problem between a fluid and elastic walls is solved by a full Eulerian fluid-structure coupling method. The method employs a uniform grid system for both fluid and solid and it does not require any mesh generation or reconstruction, aming at facilitating the practical bio-mechanical fluid-structure analysis. The availability and applicability of the developed method to systems involving complex geometries driven by a pressure gradient are shown through a comparison between the obtained numerical results and theoretical prediction, and a grid convergence test. Further, pulsating flow simulation are performed to demonstrate the effect of the pulsating amplitude on the flow rate.

DOI： 10.1299/jsmemecjo.2010.6.0_101

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

The main idea of the Eulerian fluid-structure interaction (FSI) model is derived from the idea of the multi-phase analysis on fixed Cartesian mesh. The volume fraction data is used to distinguish the fluid and structure regions, and the mixed stress on an Eulerian element is calculated with each volume fraction. In order to describe the structure deformation, which relates to the elastic stress, the left Cauchy-Green deformation tensor is introduced in a hyper-elastic material. In this paper, further development for the numerical approach is proposed such as the advection scheme of the volume data and implicit treatment for the elastic stress. The simple validation problems will be shown, and a pressure-driving capillary flow involving several biconcave materials will be also investigated.

DOI： 10.1299/jsmemecjo.2010.6.0_99

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

A full Eulerian simulation method for solving fluid-structure coupling problems has been developed. It facilitates solution of dynamic interaction problems between Newtonian fluid and hyperelastic material for given initial configuration of a multi-component geometry described by voxel-based data on a fixed Cartesian mesh. The monolithic velocity field defined over the fluid and solid domains is discretized on a fixed mesh in a finite difference manner. A solid volume fraction and a left Cauchy-Green deformation tensor are temporally updated on the Eulerian frame to distinguish between two phases and to quantify the deformation level of solid, respectively. The simulation method is applied to two-dimensional motions of biconcave neo-Hookean particles in a Poiseuille flow.

DOI： 10.1299/jsmemecjo.2010.6.0_97

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DOI： 10.11345/japannctam.59.0.188.0

J-GLOBAL

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DOI： 10.1063/1.3366385

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DOI： 10.1007/978-4-431-49022-7_6

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DOI： 10.1007/978-4-431-49022-7_24

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Meshfree particle methods are known as a powerful tool for complex numerical continuum analyses, including migration or large deformation of boundaries. However, the methods commonly tend to need higher computational costs for stable stencil calculation than mesh-based methods because the computational points, called particles, are heterogeneously distributed in a domain. To overcome this issue, we developed the mesh-constrained discrete point (MCD) approach. The MCD method can perform the stencil calculation efficiently because of constraining the arrangement of discrete points (DPs) using simple background mesh systems such as the Cartesian grids. In this study, we further develop the MCD method to address moving boundary problems. In the developed formulation, the arrangements of DP positions and related calculation masks are updated every time that follows the moving boundary. The validity of the proposed method is investigated in a simple numerical example for a moving body in two-circular channels. The calculation masks for the DPs are adequately updated even when the moving boundary crosses the background mesh.

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An efficient and scalable numerical method for massively parallel computing of fluid-structure interaction systems has been developed for biomedical applications. To facilitate the treatment of complex geometry, a full Eulerian method is employed to couple the incompressible motions of fluid and hyperelastic materials. Instead of implicitly solving the pressure Poisson equation, a novel artificial compressibility method with adaptive parameters, which are determined to guarantee the computed field to be nearly incompressible, is proposed. In both weak and strong scaling tests, the developed solver attains excellent scalability on the K computer. A sustained performance of 4.54 Pflops (42.7% of peak) has been achieved for a microchannel flow involving more than 5 million deformable bodies using 6.96x10(11) grid points with 663,552 compute cores. We study arteriole blood flows in a brain to gain insight into dynamic interactions among motions of plasma and blood cells, which are relevant to initial thrombus formations. (C) 2017 Published by Elsevier B.V.

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Computational fluid dynamics (CFD) study of the blood flow in the coiled cerebral aneurysm is one of powerful tools to explore the treatment mechanism of the endovascular coiling. Although several computational techniques were proposed to represent the realistic coil configuration in the aneurysm for the CFD studies, the CFD methodology for the blood flow analysis in the densely coiled aneurysm is still not fully discussed. The present study develops a CFD approach for the blood flow analysis in the densely coiled cerebral aneurysm without unstructured volume mesh creation. Patient-specific aneurysm geometry with realistic coil configuration was implicitly represented in a Cartesian-grid by using the volume of fraction (VOF) function. A Cartesian-grid CFD simulation was conducted in a finite difference manner with using the VOF function by the method of Weymouth and Yue (J.Compt. Phys., 2011). We conducted that two cases of numerical example of the blood flow analysis in the aneurysm prior to the coiling and after coiling with the packing density of 27%. These examples clearly exhibited that the developed CFD framework successfully resolved the fine flow characteristics around coils in the aneurysm despite the absence of explicit coil surface.

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This study investigates a feasibility for patient-specific blood flow simulation, using a set of measurement data obtained from DSA and PC-MRI with respect to a geometry and velocity. The present approach naturally satisfies the physical consistency through boundary condition. The pressure boundary values are evaluated by relaxing a misfit of velocity field between measurement and simulation based on a proportional feedback control. The investigation involves a patient-specific aneurysm model reconstructed from DSA image, where the aneurysm is developed at the bifurcation with three branches. The result shows that a difference of velocity field between the measurement of the PC-MRI and simulation is reduced to 19.8% in systole condition, and then a reasonable wall shear stress distribution can be reproduced by the use of the measurement velocity data without explicitly giving the boundary conditions. The present approach exhibits a feasibility of the simulation-based blood flow analysis for understanding patient-specific hemodynamics.

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Event date： 2016

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<p>The left ventricle (LV) plays an important role in pumping blood throughout the body. The LV motion is attributed to an electrophysiological mechanism, i.e. cardiac conduction system and excitation propagation, and mechanical mechanisms, i.e. contraction of the cardiac muscle fibers. In a sinus rhythm, the excitation propagates through the LV due to the electrophysiological stimulus of the heart muscle cells with a constant rhythm. However, in an arrhythmia, the stimulus rhythm becomes inconstant, and some arrhythmia with a severe abnormality results in a reduction of cardiac function. So far, although some computational studies considering the electrophysiological change during arrhythmia have been done, little is known about the effect of coupling mechanism between electrophysiological dynamics and the entire LV kinematic behavior. In this study, an electrophysiological-mechanical integrated LV model is developed, and the effects of the excitation propagations in both the normal and arrhythmia conditions on the LV kinematics are investigated.</p>

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For the estimation of elastic parameters for a beam model of embolization coil, this paper performs the computational simulations of tensile/compress and bending tests of the coil. The coil configuration is constructed based on the observation results by the electron microscope. The load-displacement relationship for respective mechanical tests are investigated by means of the finite element method with consideration for the contacts between coil wires itself. The tensile stiffness of the coil is in excellent agreement with the theoretical solution, whereas the compressive and bending stiffness of the coil is relatively hard due to the contacts between the coil wires.

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Hemodynamics is considered to be one of the indices to evaluate the effects of the treatment by coil embolization for cerebral aneurysms. For the sake of detailed analysis of hemodynamics in coil-embolized aneurysms, we develop a virtual coil model based on the mechanical theory that the coil deforms toward minimizing the elastic energy, and represent a realistic configuration of the embolized coils in the aneurysm by the insertion simulation. Then, the blood flow analysis is done by solving the N.S. and continuity equations numerically with the finite volume method using polyhedral mesh. The coil insertion simulation demonstrated that almost uniform distribution of the coil in the aneurysm was achieved at over 10% packing density of the coil. The blood flow analysis using the virtual coil model showed that the flow momentum inside the aneurysm was reduced to less than 10% by coil embolization with a packing density over 20%. In comparison to the simulation results using a porous media model for the embolized coil, there was no significant difference in the reduction ratio of the flow momentum in the aneurysm by coil embolization. However, local flow dynamics evaluated by the flow voracity was different in the virtual coil model and the porous media model, in particular at the neck region of the aneurysm.

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Event date： 2014

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We have developed novel numerical methods for fluid-structure and fluid-membrane interaction problems. The basic equation set is formulated in a full Eulerian framework. The method is based on the finite difference volume-of-fluid scheme with fractional step algorithm. It is validated through a numerical solution to a deformable vesicle problem, and applied to blood flows including red blood cells (RBCs) and platelets. Further, to gain insight into the mechanism of thrombus formation, a stochastic Monte Carlo model to describe the platelet-vessel wall interaction is incorporated into the Eulerian method. The effect of the RBCs on the platelet motion is discussed. (C) 2013 Published by Elsevier Ltd.

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We have been working on the development of a full Eulerian formulation method for solving fluid-structure interaction problems.The original method [1] has been extended for fluid-membrane interaction problems [2].This method is applied to the blood flows containing red blood cells and platelets.Then,it is further extended to multiscale thrombosis simulation,which couples Monte-Carlo simulations for the molecular scale protein-protein interactions with continuum scale simulations.These simulators are developed for the massively parallel computation.The results reveal that the flow fluctuation given by the presence of red blood cells plays an important role to make the platelets adhering on the vessel wall.

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A full Eulerian finite difference method has been developed for solving a dynamic interaction problem between Newtonian fluid and hyperelastic material. It facilitates to simulate certain classes of problems, such that an initial and neutral configuration of a multi-component geometry converted from voxel-based data is provided on a fixed Cartesian mesh. A solid volume fraction, which has been widely used for multiphase flow simulations, is applied to describing the multi-component geometry. The temporal change in the solid deformation is described in the Eulerian frame by updating a left Cauchy-Green deformation tensor, which is used to express constitutive equations for incompressible hyperelastic materials. The present Eulerian approach is confirmed to well reproduce the material deformation in the lid-driven flow and the particle-particle interaction in the Couette flow computed by means of the finite element method. It is applied to a Poiseuille flow containing biconcave neo-Hookean particles. The deformation, the relative position and orientation of a pair of particles are strongly dependent upon the initial configuration. The increase in the apparent viscosity is dependent upon the developed arrangement of the particles. Copyright © 2011 by ASME.

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Event date： 2010.9

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A full Eulerian simulation method for solving fluid-structure coupling problems has been developed. It facilitates solution of dynamic interaction problems between Newtonian fluid and hyperelastic material for given initial configuration of a multi-component geometry described by voxel-based data on a fixed Cartesian mesh. The monolithic velocity field defined over the fluid and solid domains is discretized on a fixed mesh in a finite difference manner. A solid volume fraction and a left Cauchy-Green deformation tensor are temporally updated on the Eulerian frame to distinguish between two phases and to quantify the deformation level of solid, respectively. The simulation method is applied to two-dimensional motions of biconcave neo-Hookean particles in a Poiseuille flow.

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Event date： 2010.9

Language：Japanese  

Abstract An interaction problem between a fluid and elastic walls is solved by a full Eulerian fluid-structure coupling method. The method employs a uniform grid system for both fluid and solid and it does not require any mesh generation or reconstruction, aming at facilitating the practical bio-mechanical fluid-structure analysis. The availability and applicability of the developed method to systems involving complex geometries driven by a pressure gradient are shown through a comparison between the obtained numerical results and theoretical prediction, and a grid convergence test. Further, pulsating flow simulation are performed to demonstrate the effect of the pulsating amplitude on the flow rate.

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Event date： 2010.9

Language：Japanese  

The main idea of the Eulerian fluid-structure interaction (FSI) model is derived from the idea of the multi-phase analysis on fixed Cartesian mesh. The volume fraction data is used to distinguish the fluid and structure regions, and the mixed stress on an Eulerian element is calculated with each volume fraction. In order to describe the structure deformation, which relates to the elastic stress, the left Cauchy-Green deformation tensor is introduced in a hyper-elastic material. In this paper, further development for the numerical approach is proposed such as the advection scheme of the volume data and implicit treatment for the elastic stress. The simple validation problems will be shown, and a pressure-driving capillary flow involving several biconcave materials will be also investigated.

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Event date： 2010.6

Language：Japanese  

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Event date： 2010

Language：Japanese  

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Event date： 2010

Language：Japanese  

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Event date： 2010

Language：English  

A new simulation method for solving fluid-structure coupling problems suitable for voxel-based geometry has been developed. All the basic equations are numerically solved on a fixed Cartesian grid in a finite difference scheme. An incompressible fluid flow solver is extended to the incompressible fluid-structure system. A volume-of-fluid approach is applied to describing the multi-component geometry. The temporal change in the solid deformation is described on the Eulerian frame by updating a left Cauchy-Green deformation tensor, which expresses constitutive equations of the hyperelastic Cauchy stress for e.g. neo-Hookean material. Two validations are made: one is a comparison with the available simulation of the solid motion in the lid-driven flow (Zhao et al. (2008) J. Comput. Phys. 227, 3114), in which the deformed solid motion is solved in the finite element approach, the other is an examination of the reversibility in shape of the hyperelastic material under no stress situation. The present method is confirmed to well capture the material deformation and the reversal.

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Event date： 2010

Language：Japanese  

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Event date： 2009.10

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Event date： 2009.10

Language：Japanese  

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Event date： 2009.9

Language：Japanese  

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Event date： 2009.9

Language：Japanese  

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Event date： 2009.5

Language：Japanese  

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Event date： 2009.5

Language：Japanese  

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Event date： 2009

Language：Japanese  

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Event date： 2009

Language：Japanese  

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Event date： 2009

Language：Japanese  

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Event date： 2009

Language：Japanese  

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Event date： 2009

Language：Japanese  

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Event date： 2009

Language：Japanese  

A new simulation method for solving fluid-structure coupling problems suitable for voxel-based geometry has been developed. All the basic equations are numerically solved on a fixed Cartesian grid in a finite difference scheme. An incompressible fluid flow solver is extended to the incompressible fluid-structure system. A volume-of-fluid approach is applied to describing the multi-component geometry. The temporal change in the solid deformation is described on the Eulerian frame by updating a left Cauchy-Green deformation tensor, which expresses constitutive equations of the hyperelastic Cauchy stress for e.g. Mooney-Rivlin material. The present method is confirmed to well capture the solid deformation.

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Event date： 2008.10

Language：Japanese  

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Event date： 2008.5

Language：Japanese  

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Event date： 2008.5

Language：Japanese  

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Event date： 2008

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Event date： 2008

Language：Japanese  

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Event date： 2008

Language：Japanese  

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Event date： 2007.5

Language：Japanese  

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Event date： 2007.5

Language：Japanese  

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Event date： 2007.5

Language：Japanese  

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Event date： 2007

Language：English  

Most of the existing numerical models for the simulation of Tsunami are based on the 2D shallow water equations. However, for many situations, it is necessary to use the 3D model in addition to the shallow water models to evaluate the damage in the coast region with a reliable accuracy. So, we propose the multi-scale warning system for Tsunami by coupling the 2D shallow water model and the 3D Navier-Stokes model that solves explicitly the free water surface to cover the physical phenomena that have diverse scales in both time and space. As a part of such a system, we, in this paper, present the essential numerics of the models based on the CIP/MM FVM (CIP/Multi-Moment Finite Volume Method) and some simulation results with the real geographical data for the 2D large-scale cases.

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Event date： 2007

Language：English  

We simulated fluid-structure interaction problems using the immersed interface method on a Cartesian grid. The immersed interface method allows explicit specification of the jump conditions across the fluid-structure interface, yielding high order accuracy. We in this study evaluated the jump condition with one-side stencil over the interface. The resulting formulation is able to deal with structures even smaller than mesh side. We use local-based and high-order numerical scheme which involves the derivative jump conditions to get high-order accuracy.
The present numerical method were verified by some numerical examples.

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Event date： 2007

Language：Japanese  

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Event date： 2006.9

Language：Japanese  

Most of the existing numerical models for the simulation of Tsunami are based on the 2D shallow water equations. However, for many situations, it is necessary to use the 3D model in addition to the shallow water models to evaluate the damage in the coast region with a reliable accuracy. So, we propose the multi-scale warning system for Tsunami by connecting these models to cover the physical phenomena that have diverse scales in both time and space. In this paper, we present the formulation of the 2D shallow water wave model based on the CIP/MM-FVM with the MOC. In addition, we construct the formulation for the source term preserved the fundamental balance between the source term and the flux gradient. Finally, we apply the present model to some "real-case" numerical experiments.

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Event date： 2006.9

Language：Japanese  

We propose a high-order finite volume method based on multi-moment, namely constrained interpolation profile/multi-moment finite volume method (CIP/MM FVM), on the icosahedral spherical grid. In this method, two kinds of moments are defined as model variables on physical field, for example the point value (PV) and the volume-integrated average (VIA), and updated independently in time. Therefore, a CIP/MM FVM appears to be more attractive regarding the stability and flexibility in comparison with other conventional single-moment finite volume methods that use only the VIA as the model variable. The icosahedral spherical grid has a significant advantage of grid uniformity. We have developed a CIP/MM FVM formulations for the advection equation and the shallow-water equations on the sphere, and carried out some numerical experiments to varify the numerical schemes.

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Event date： 2006

Language：Japanese  

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Event date： 2005.11

Language：Japanese  

We propose a conservative scheme that suppresses numerical oscillation on triangular unstructured grids. We use "multi-moment" that is one of the features of the CIP method. Three types of so-called "moments", defined as the volume-integrated average (VIA), the point value (PV) and surface-integrated average (SIA) of physical field are used as the prognostic variables to be carried forward in time separately. VIA is updated by a flux formulation, and PV and SIA are updated by a semi-Lagrangian scheme. A 2D quadratic polynomial can be construction over a single triangular element. Numerical oscillation is suppressed by limiting the gradient of a polynomial. Shallow water equation is solved by using Method of Characteristics that is suitable for semi-Lagrangian method. The time-integrated average of flux for updating VIA is approximated by the trajectory-integrated average of Riemann invariant. The proposed method has little numerical oscillation and appears to be robust to different numerical grids by some numerical tests.

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Event date： 2005.9

Language：Japanese  

In this paper, we introduce the multi-block method to the CIP/Multi-Moment Finite Volume Method (CIP/MM-FVM) to make the numerical model more flexible and more efficient in the presence of complex geometry. Because the stencil required for the reconstruction in the CIP/MM-FVM is compact, the halo region for the block boundary is of only one grid spacing. The accuracy and the conservatively of the original CIP/MM-FVM is maintained by imposing proper conditions at the common boundary of two different blocks. Numerical experiments have been carried out to verify the proposed method.

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Event date： 2005.9

Language：Japanese  

We propose a 4th-order conservative scheme for transport equation on triangular unstructured grids based on the underlying concept of the CIP method. Two types of so-called "moments", defined as the volume integrated average (VIA) and the point value (PV) of physical field are used as the prognostic variables to be carried forward in time separately. VIA is updated by a flux formulation, and PVs are updated by a semi-Lagrangian scheme. A 2D cubic polynomial can be construction over a single triangular element. The 4^<th>-order accuracy of the numerical scheme is verified by numerical tests. The proposed method appears to be very robust to different unstructured grids.

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Event date： 2005.9

Language：Japanese  

This paper presents rational function based fully multi-dimensional advection schemes for structured and unstructured grids of a quadrilateral geometry. For the structured grid, a fully 2D rational interpolation function is constructed by combining two 1D sweeps based on the 1D rational function with 3 degrees of freedoms, and is convexity preserving. For the unstructured, the interpolation function is constructed according to the same procedure as in the structured grid after each control volume is mapped to a rectangle. Numerical tests of advection transport show that the constructed rational interpolation functions effectively eliminate the numerical oscillations and give well-regulated solutions.

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Event date： 2005.9

Language：Japanese  

Most of the existing numerical models for the simulation of Tsunami are based on the 2D shallow water equations. However, for many situations, it is necessary to use the 3D model in addition to the shallow water models to evaluate the damage in the coast region with a reliable accuracy. So, we propose the multi-scale warning system for Tsunami by connecting these models to cover the physical phenomena that have diverse scales in both time and space. In this paper, we present the formulation of the 2D shallow water wave model based on the CIP/Multi-Moment concept and the theory of characteristics. As the first step of this system, we apply CIP-CSL scheme to the rectangular structured grid and the triangle unstructured grid.

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Event date： 2005

Language：Japanese  

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Event date： 2004

Language：Japanese  

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