Drag force on a microrobot propelled through blood

Controlling microrobot locomotion in vessels and capillaries is crucial for precise drug delivery and minimally invasive surgeries. However, this is challenging due to the complex interactions with red blood cells (RBCs) and the difficulty navigating within the dense environment. Here, we construct a numerical framework to evaluate the relative resistance coefficient ( $${C}_{{{{{{{{\rm{r}}}}}}}}}^{* }$$ ) of a microrobot propelled through RBC suspensions. Our experiments validate the numerical results. We find that $${C}_{{{{{{{{\rm{r}}}}}}}}}^{* }$$ increases for smaller microrobots and higher hematocrit levels, while magnetic force strength weakly impacts $${C}_{{{{{{{{\rm{r}}}}}}}}}^{* }$$ . $${C}_{{{{{{{{\rm{r}}}}}}}}}^{* }$$ is smaller than the resistance coefficient of a macroscale robot estimated from the apparent viscosity of the RBC suspension. The aspect ratio of a prolate ellipsoidal microrobot influences $${C}_{{{{{{{{\rm{r}}}}}}}}}^{* }$$ along its long-axis direction. Additionally, machine learning accurately predicts $${C}_{{{{{{{{\rm{r}}}}}}}}}^{* }$$ . These insights could enhance the design and control of microrobots for medical applications. Controlling microrobot movement in blood vessels is vital for medical treatments but is challenging due to red blood cells. This study combines simulations, experiments, and machine learning to demonstrate how hematocrit levels and robot geometry affect its locomotion characteristics in blood