A Fluid-Structure Interaction Analysis of Blood Clot Motion in a Branch of Pulmonary Arteries.

INTRODUCTION: Pulmonary embolism (PE) is one of the most prevalent diseases amid hospitalized patients taking many people's lives annually. This phenomenon, however, has not been investigated via numerical simulations. METHODS: In this study, an image-based model of pulmonary arteries has been constructed from a 44-year-old man's computed tomography images. The fluid-structure interaction method was used to simulate the motion of the blood clot. In this regard, Navier-Stokes equations, as the governing equations, have been solved in an arbitrary Lagrangian-Eulerian (ALE) formulation. RESULTS: According to our results, the velocity of visco-hyperelastic model of the emboli was relatively higher than the emboli with hyperelastic model, despite their similar behavioral pattern. The stresses on the clot were also investigated and showed that the blood clot continuously sustained stresses greater than 165 Pa over an about 0.01 s period, which can cause platelets to leak and make the clot grow or tear apart. CONCLUSIONS: It could be concluded that in silico analysis of the cardiovascular diseases initiated from clot motion in blood flow is a valuable tool for a better understanding of these phenomena.

Zigzag microchannel for rigid inertial separation and enrichment (Z-RISE) of cells and particles.

Separation and enrichment of target cells prior to downstream analyses is an essential pre-treatment step in many biomedical and clinical assays. Separation techniques utilizing simple, cost-effective, and user-friendly devices are highly desirable, both in the lab and at the point of need. Passive microfluidic approaches, especially inertial microfluidics, fit this brief perfectly and are highly desired. Using an optimized additive manufacturing technique, we developed a zigzag microchannel for rigid inertial separation and enrichment, hereafter referred to as Z-RISE. We empirically showed that the Z-RISE device outperforms equivalent devices based on curvilinear (sinusoidal), asymmetric curvilinear, zigzag with round corners, or square-wave formats and modelled this behavior to gain a better understanding of the physics underpinning the improved focusing and separation performance. The comparison between rigid and soft zigzag microchannels reveals that channel rigidity significantly affects and enhances the focusing performance of the microchannel. Compared to other serpentine microchannels, zigzag microfluidics demonstrates superior separation and purity efficiency due to the sudden channel cross-section expansion at the corners. Within Z-RISE, particles are aligned in either double-side or single-line focusing positions. The transition of particles from a double-focusing line to a single focusing line introduced a new phenomenon referred to as the plus focusing position. We experimentally demonstrated that Z-RISE could enrich leukocytes and their subtypes from diluted and RBC lysed blood while depleting dead cells, debris, and RBCs. Z-RISE was also shown to yield outstanding particle or cell concentration with a concentration efficiency of more than 99.99%. Our data support the great potential of Z-RISE for applications that involve particle and cell manipulations and pave the way for commercialization perspective in the near future.

Numerical and Experimental Study of Cross-Sectional Effects on the Mixing Performance of the Spiral Microfluidics.

Mixing at the microscale is of great importance for various applications ranging from biological and chemical synthesis to drug delivery. Among the numerous types of micromixers that have been developed, planar passive spiral micromixers have gained considerable interest due to their ease of fabrication and integration into complex miniaturized systems. However, less attention has been paid to non-planar spiral micromixers with various cross-sections and the effects of these cross-sections on the total performance of the micromixer. Here, mixing performance in a spiral micromixer with different channel cross-sections is evaluated experimentally and numerically in the Re range of 0.001 to 50. The accuracy of the 3D-finite element model was first verified at different flow rates by tracking the mixing index across the loops, which were directly proportional to the spiral radius and were hence also proportional to the Dean flow. It is shown that higher flow rates induce stronger vortices compared to lower flow rates; thus, fewer loops are required for efficient mixing. The numerical study revealed that a large-angle outward trapezoidal cross-section provides the highest mixing performance, reaching efficiencies of up to 95%. Moreover, the velocity/vorticity along the channel length was analyzed and discussed to evaluate channel mixing performance. A relatively low pressure drop (<130 kPa) makes these passive spiral micromixers ideal candidates for various lab-on-chip applications.

Particle movement and fluid behavior visualization using an optically transparent 3D-printed micro-hydrocyclone.

A hydrocyclone is a macroscale separation device employed in various industries, with many advantages, including high-throughput and low operational costs. Translating these advantages to microscale has been a challenge due to the microscale fabrication limitations that can be surmounted using 3D printing technology. Additionally, it is difficult to simulate the performance of real 3D-printed micro-hydrocyclones because of turbulent eddies and the deviations from the design due to printing resolution. To address these issues, we propose a new experimental method for the direct observation of particle motion in 3D printed micro-hydrocyclones. To do so, wax 3D printing and soft lithography were used in combination to construct a transparent micro-hydrocyclone in a single block of polydimethylsiloxane. A high-speed camera and fluorescent particles were employed to obtain clear in situ images and to confirm the presence of the vortex core. To showcase the use of this method, we demonstrate that a well-designed device can achieve a 95% separation efficiency for a sample containing a mixture of (desired) stem cells and (undesired) microcarriers. Overall, we hope that the proposed method for the direct visualization of particle trajectories in micro-hydrocyclones will serve as a tool, which can be leveraged to accelerate the development of micro-hydrocyclones for biomedical applications.