# A Variable Cross-Section Microfluidic Channel for Simultaneous Reproduction of Low Oscillatory and Pulsatile Wall Shear Stress at the Carotid Bifurcation: A Computational Fluid Dynamics-Based Study

## TL;DR

This study designs a microfluidic channel to replicate complex blood flow patterns at the carotid bifurcation, helping to understand how different wall shear stresses affect vascular health.

## Contribution

A novel microfluidic channel is designed to simultaneously reproduce both pulsatile and oscillatory wall shear stress patterns found in the carotid bifurcation.

## Key findings

- The optimized microfluidic channel successfully reproduces low oscillatory wall shear stress at a stepped section resembling the carotid sinus.
- Vortex formation in the stepped section is key to generating low oscillatory wall shear stress, influenced by step height and flow rate.
- The design enables simultaneous simulation of pulsatile wall shear stress in a downstream uniform section.

## Abstract

Pulsatile blood flow generates complex wall shear stress (WSS) patterns at the carotid bifurcation, which critically regulate endothelial function and structure. While physiological pulsatile WSS (PWSS) is essential for maintaining vascular health, low oscillatory WSS (OWSS) near the carotid sinus is closely associated with endothelial dysfunction, atherosclerotic plaque formation, and stenosis. Reproducing these hemodynamic conditions in vitro is therefore crucial for investigating endothelial mechanobiology and elucidating the pathogenesis of atherosclerosis. Although microfluidic technologies have emerged as promising platforms for simulating either pulsatile or oscillatory WSS, a system capable of simultaneously replicating both characteristic waveforms—as found in vivo at the carotid bifurcation—remains undeveloped. In this study, we designed a variable cross-section microfluidic channel using Computational Fluid Dynamics (CFD) simulations. Numerical results demonstrate that the optimized channel accurately reproduces low OWSS at a stepped section emulating the carotid sinus, alongside high PWSS in a downstream uniform section. Vortex formation induced by the step structure is identified as key to generating low OWSS, influenced by step height, channel width ratio, and input flow rate. This work provides a novel and robust methodology for designing microfluidic systems that mimic complex hemodynamic microenvironments, facilitating future studies on the interplay between distinct WSS patterns and endothelial dysfunction.