Development of Ultrasound Phantom Made of Transparent Material: Feasibility of Optical Particle Image Velocimetry.

OBJECTIVE: The need for ultrasound flow phantoms to validate ultrasound systems requires the development of materials that can clearly visualize the flow inside for measurement purposes. METHODS: A transparent ultrasound flow phantom material composed of poly(vinyl alcohol) hydrogel (PVA-H) with dimethyl sulfoxide (DMSO) and water solution manufactured using the freezing method and mixed with quartz glass powder to exhibit scattering effects is proposed. To achieve transparency of the hydrogel phantom, the refractive index (RI) was changed to match that of the glass by modifying the PVA concentration and the ratio of DMSO to water in the solvent. The feasibility of optical particle image velocimetry (PIV) was verified by comparing an acrylic rectangular cross-section channel with a rigid wall. After the feasibility tests, an ultrasound flow phantom was fabricated to conduct ultrasound B-mode visualization and Doppler-PIV comparison. DISCUSSION: The results revealed that the PIV measured through PVA-H material exhibited 0.8% error in the measured maximum velocity compared with PIV through the acrylic material. B-mode images are similar to real tissue visualization with a limitation of a higher sound velocity, when compared with human tissue, of 1792 m/s. Doppler measurement of the phantom revealed approximately 120% and 19% overestimation of maximum and mean velocities, respectively, compared with those from PIV. CONCLUSION: The proposed material possesses the advantage of the single-phantom ability to improve the ultrasound flow phantom for validation of flow.

Endothelial Cell Distribution After Flow Exposure With Two Stent Struts Placed in Different Angles.

Stent implantation has been a primary treatment for stenosis and other intravascular diseases. However, the struts expansion procedure might cause endothelium lesion and the structure of the struts could disturb the blood flow environment near the wall of the blood vessel. These changes could damage the vascular innermost endothelial cell (EC) layer and pose risks of restenosis and post-deployment thrombosis. This research aims to investigate the effect of flow alterations on EC distribution in the presence of gap between two struts within the parallel flow chamber. To study how the gap presence impacts EC migration and the endothelialization effect on the surface of the struts, two struts were placed with specific orientations and positions on the EC layer in the flow chamber. After a 24-h exposure under wall shear stress (WSS), we observed the EC distribution conditons especially in the gap area. We also conducted computational fluid dynamics (CFD) simulations to calculate the WSS distribution. High EC-concentration areas on the bottom plate corresponded to the high WSS by the presence of gap between the two struts. To find the relation between the WSS and EC distributions on the fluorescence images, WSS condition by CFD simulation could be helpful for the EC distribution. The endothelialization rate, represented by EC density, on the downstream sides of both struts was higher than that on the upstream sides. These observations were made in the flow recirculation at the gap area between two struts. On two side surfaces between the gaps, meaning the downstream at the first and the upstream at the second struts, EC density differences on the downstream surfaces of the first strut were higher than on the upstream surfaces of the second strut. Finally, EC density varied along the struts when the struts were placed at tilted angles. These results indicate that, by the presence of gap between the struts, ECs distribution could be predicted in both perpendicular and tiled positions. And tiled placement affect ECs distribution on the strut side surfaces.

Endothelial cell distributions and migration under conditions of flow shear stress around a stent wire.

BACKGROUND: Blood vessels are constantly exposed to flow-induced stresses, and endothelial cells (ECs) respond to these stresses in various ways. OBJECTIVE: In order to facilitate endothelialization after endovascular implantation, cell behaviors around a metallic wire using a flow circulation system are observed. METHODS: A parallel flow chamber was designed to reproduce constant shear stresses (SSs) on cell surfaces and to examine the effects of a straight bare metal wire on cell monolayers. Cells were then exposed to flow for 24 h under SS conditions of 1, 2, and 3 Pa. Subsequently, cell distributions were observed on the plate of the flow chamber and on the surface of the bare metal wire. Flow fields inside the flow chamber were analyzed using computational fluid dynamics under each SS condition. RESULTS: After 24 h, ECs on the bottom plate were concentrated toward the area of flow reattachment. The matching of higher cell density and CFD result suggests that flow-induced stimuli have an influence on EC distributions. CONCLUSION: Typical cell concentration occurs on dish plate along the vortexes, which produces large changes in SSs on cell layer.

Effect of a notch at the distal end of a microcatheter on vein deformation in segmental adrenal venous sampling: a preliminary study using computational fluid dynamics.

This study aimed to evaluate the effect of a notch at the distal end of a microcatheter on vein deformation in segmental adrenal venous sampling. A three-dimensional fluid-structure interaction simulation was performed using commercial finite element software. A computational model of a vein with a catheter inserted into it was constructed. The outer and inner diameters of the vein were 0.9 mm and 0.6 mm, respectively, whereas those of the catheter were 0.6 mm and 0.5 mm, respectively. The velocity of the blood flow at the outlet was 85 mm/s. The pressure at the inlet was 0 Pa. The mesh consisted of approximately 660,000 elements. The effect of the number (0-4) and shape (no notch, 1/4 circular, 1/3 circular, semicircular, 2/3 circlecircular, and 3/4 circular) of the notches at the distal end of the microcatheter on the vein deformation when a suction pressure was applied was evaluated. The venous wall displacement was the smallest with the one-notch catheter, followed by the four-notch catheter, and was the smallest with the catheter having 1/4-circular notches, followed by the one with 1/3-circular notches. In conclusion, microcatheters having one notch and 1/4-circular notches reduce vein deformation and lead to successful segmental adrenal venous sampling. Graphical abstract Comparing catheters having different notch shapes.

Multiobjective design optimization of stent geometry with wall deformation for triangular and rectangular struts.

The stent geometrical design (e.g., inter-strut gap, length, and strut cross-section) is responsible for stent-vessel contact problems and changes in the blood flow. These changes are crucial for causing some intravascular abnormalities such as vessel wall injury and restenosis. Therefore, structural optimization of stent design is necessary to find the optimal stent geometry design. In this study, we performed a multiobjective stent optimization for minimization of average stress and low wall shear stress ratio while considering the wall deformation in 3D flow simulations of triangular and rectangular struts. Surrogate-based optimization with Kriging method and expected hypervolume improvement (EHVI) are performed to construct the surrogate model map and find the best configuration of inter-strut gap (G) and side length (SL). In light of the results, G-SL configurations of 2.81-0.39 and 3.00-0.43 mm are suggested as the best configuration for rectangular and triangular struts, respectively. Moreover, considering the surrogate model and flow pattern conditions, we concluded that triangular struts work better to improve the intravascular hemodynamics. ᅟ Graphical abstract.

Computational Fluid Dynamics Analysis to Predict Endothelial Cells Migration During Flow Exposure Experiment With Placement of Two Stent Wires.

Stent deployment is currently used for many cardiovascular treatments. During its application, the presence of the stent inside the blood vessel will indeed cause some change in both flow environment and also vessel wall's cellular conditions. This research intends to learn about the flow phenomenon of how vessel wall endothelial cells (ECs) react to the presence of stent wires within a microfluidic flow chamber environment. Computational fluid dynamics (CFD) simulation analysis of the microfluidic flow chamber system has been performed for observing the hemodynamics phenomena in the chamber. Moreover, CFD method also can be beneficial as a planning step for a successful experimental study. We found that under the two wires configurations, high wall shear stress (WSS) area is developed on the downstream side of the wires. Based on the analysis of WSS and WSS gradients (WSSG) conditions, ECs morphological change and migration are likely to occur some specific area.

Reproduction method for dried biomodels composed of poly (vinyl alcohol) hydrogels.

Models mimicking the realistic geometries and mechanical properties of human tissue are requiring ever-better materials. Biomodels made of poly (vinyl alcohol) are particularly in demand, as they can be used to realistically reproduce the characteristics of blood vessels. The reproducibility of biomodels can be altered due to dehydration that is observed after long periods of usage. In order to improve their usability, one should consider the method used to reproduce them; however, few studies have reported a method reproduce biomodels. This study proposes a novel reproduction method for biomodels that allows them to quickly and easily reproduce their geometric and mechanical properties. Specimens of the dried biomodels were reformed through immersion in temperature-controlled water. Our results show that water at 35 °C can be effective to reproduce both the geometric and mechanical properties of the specimens. X-ray diffraction (XRD) measurements revealed that water immersion can reform the crystal structure of the pre-dried specimens, and images obtained using micro-computed tomography acquisition show that the geometry of the specimens can be reformed by water immersion without introducing any defects. These results indicate that the proposed method can lead to high reproducibility of both the original geometric and mechanical properties of the dried biomodels.

In search for a better stent: Surrogate based multi-objective optimization of stent design under influence of vessel wall deformation.

Stenting is known as one of the main treatment procedure for some intravascular abnormalities such as stenosis and aneurysm. In recent years, stent optimization has been conducted by several research groups in order to increase its treatment efficacy. If we can observe post-deployment behavior on the blood vessel with respect to different stent designs, this observation will be useful in the design process. Kriging surrogate model based on fluid flow simulation on a deformed vessel wall was developed in order to observe this behavior. Multi-objectives optimization was performed with configurations of gap and size as design variables. In this research, percentage of low wall shear stress (WSS) area and average mechanical stress along the deployment area were set as the objective functions. We can recommend that strut with medium size around 100 - 250 micron with a relatively big inter-strut gap is suitable for achieving the optimize criteria. This is because on this range, acceptable optimized value of both objectives functions are successfully obtained.