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Updated: Feb 26, 2026
Micro-particle Image Velocimetry for Velocity Profile Measurements of Micro Blood Flows
Published on: April 25, 2013
Capture of microparticles by bolus flow of red blood cells in capillaries
Naoki Takeishi1, Yohsuke Imai2
1Institute for Frontier Life and Medical Sciences, Kyoto University, Department of Biosystems Science, 53 Shogoin-Kawara-cho, Sakyo, Kyoto, 606-8507, Japan.
Abstract:
Previous studies have concluded that microparticles (MPs) can more effectively approach the microvessel wall than nanoparticles because of margination. In this study, however, we show that MPs are not marginated in capillaries where the vessel diameter is comparable to that of red blood cells (RBCs). We numerically investigated the behavior of MPs with a diameter of 1 μm in various microvessel sizes, including capillaries. In capillaries, the flow mode of RBCs shifted from multi-file flow to bolus (single-file) flow, and MPs were captured by the bolus flow of the RBCs instead of being marginated. Once MPs were captured, they rarely escaped from the vortex-like flow structures between RBCs. These capture events were enhanced when the hematocrit was decreased, and reduced when the shear rate was increased. Our results suggest that microparticles may be rather inefficient drug carriers when targeting capillaries because of capture events, but nanoparticles, which are more randomly distributed in capillaries, may be more effective carriers.
Insights
Microparticles (MPs) are not marginated in capillaries as previously thought. Instead, they get captured by red blood cell (RBC) bolus flow, suggesting nanoparticles may be better drug carriers for capillaries.
Area of Science:
- Biomedical Engineering
- Fluid Dynamics
- Nanotechnology
Background:
- Previous research suggested microparticles (MPs) are superior to nanoparticles for microvessel delivery due to margination.
- Margination is the phenomenon where larger particles move towards the vessel wall.
Purpose of the Study:
- To investigate the behavior of microparticles (MPs) in capillaries, challenging the assumption of margination.
- To compare the delivery efficiency of microparticles and nanoparticles in capillary environments.
Main Methods:
- Numerical simulations were employed to study the behavior of 1 μm MPs in microvessels of varying sizes, including capillaries.
- Analysis focused on particle flow dynamics, red blood cell (RBC) flow patterns, and capture events within the microvasculature.
Main Results:
- In capillaries, MPs were captured by red blood cell (RBC) bolus flow, not marginated.
- MPs exhibited limited escape from vortex-like flow structures once captured.
- Capture events were more frequent at lower hematocrit and less frequent at higher shear rates.
Conclusions:
- Microparticles may be inefficient drug carriers for capillaries due to capture by RBCs.
- Nanoparticles, with their more random distribution, might be more effective carriers for capillary targeting.
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