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.

This study evaluates the analytical performance of a newly developed miniaturized disposable U-tube for an automated blood viscometer and compares it to conventional viscometers. Whole blood viscosity (WBV), essential for circulatory function, exhibits non-Newtonian behavior, posing challenges for measurement at low shear rates. The blood viscometer, based on a scanning capillary tube method, used disposable U-tubes to measure viscosities across a shear rate range of 1s⁻¹ to 1,000s⁻¹. Precision evaluation showed stable coefficients of variation (CV) across different viscosity levels. Repeatability assessment indicated consistent CV values, demonstrating the reliability of the device. The agreement with the LV-III Brookfield viscometer and MCR 92 Rheometer was analyzed using Bland-Altman plots, which revealed minor systematic biases and consistent differences across the measurement range. Correlation analysis using Passing-Bablok regression showed high correlation coefficients (R > 0.96) with regression slopes close to 1. The newly developed miniaturized disposable U-tube exhibits excellent precision, reliable repeatability, and high correlation with established methods, enhancing laboratory productivity and offering potential for clinical applications. Further studies with human blood samples are recommended to confirm its clinical applicability.