This research explores the mechanical behavior of whole blood as a shear-thinning fluid and examines yield stress as a crucial parameter for evaluating flow properties in the microvasculature. While previous studies have primarily focused on whole blood viscosity (WBV), this study presents an engineering-based approach to quantitatively evaluate the yield stress of non-Newtonian whole blood using a U-shaped capillary tube. A custom-designed scanning capillary tube, incorporating a biocompatible U-shaped capillary channel, was employed to determine whole blood viscosity (WBV) across shear rates from 1 to 1,000 s⁻1. Yield stress was estimated by extrapolating the shear stress-shear rate relationship using a non-Newtonian shear-thinning flow model. The analysis revealed a strong cubic correlation between hematocrit and yield stress, suggesting an increased risk of flow impairment in the microvasculature with elevated hematocrit levels. This work emphasizes the critical influence of yield stress in regulating microvascular blood flow, particularly under low-shear conditions.

Abstract
1. Introduction
2. Materials and Methods
    2.1 A biocompatible U-shaped tube with capillarychannel
    2.2 Determination of WBV and yield stress
    2.3 Sample preparation and analytical procedure
3. Results and Discussion
    3.1 Viscosity comparison
    3.2 Relationship between hematocrit and yieldstress
4. Conclusion
Declaration of Interests
Acknowledgement
References

• 정진무(Department of Mechanical Design Engineering, College of Engineering, Jeonbuk National University, Hemorheology Research Institute, Jeonbuk National University) | Jinmu Jung
• 권덕철(Industry-Academic Cooperation Office, Jeonbuk National University) | Deok-Cheol Kwon Corresponding author