Cell-free layer development process in the entrance region of microvessels.

We simulated red blood cell flows through a finite length channel with a two-dimensional immersed boundary lattice Boltzmann model. The local instantaneous variation in wall-cell distance has been examined in details, and a nominal cell-free layer (CFL) thickness has been proposed. The CFL development process along the channel has been then analyzed, showing that the CFL thickness profile can be basically split into two regimes: the initial rapid increase due to cell migration and the later gradual growth due to cell reorganization. Effects of various hemorheological factors, such as rigidity, aggregation, hematocrit, and channel width, have also been investigated. The development length of the CFL to 90% of its final width ranges from 150 to 300 μm, and the development length is sensitive to changes in hemorheological conditions. The correlation between the CFL features and hemorheological parameters has also been explored. The simulation results have been compared to available experimental studies, and qualitative agreement has been noticed. In spite of the model limitations, this study reveals the complexity of CFL development process, and it could be useful for better understanding relevant processes and phenomena in the microcirculation.