Microswimmers Navigating the Blood: Unraveling Locomotion Characteristics

Microrobots capable of navigating through the intricate network of blood vessels hold significant promise for various medical applications. Due to the high volume fraction of blood cells in blood, microrobots must propel themselves by rearranging the surrounding blood cells to move effectively. However, the most effective swimming mechanism for propulsion in blood remains unknown. In this study, we numerically investigate two different microrobots propelled through blood: non-surface active and surface active microswimmers. We systematically vary parameters such as the capillary number, hematocrit, magnetic torque exerted on the microrobot, and microrobot to red blood cell (RBC) radius ratio to evaluate their impact on microrobot behavior in complex in vivo environments.

Our findings reveal that a surface active microrobot is by far more efficient in moving through blood than a non-surface active microrobot. This is because the surface velocity of the microrobot pushes the blood cells laterally, allowing them to propel themselves into the hole they are digging. When the microrobot size is comparable to a red blood cell, the puller microrobot swims faster than the pusher microrobot. However, when the microrobot size becomes much smaller, the pusher microrobot swims faster than the puller microrobot. These results offer valuable insights into the design of microrobots efficiently navigating through blood for targeted drug delivery and minimally invasive medical procedures.