Efficient Blood Propulsion of Squirmer-Type Microrobots

Microrobots capable of navigating through the intricate network of blood vessels hold significant promise for various medical applications. Blood contains high volume fraction of blood cells, a microrobot must propel itself by rearranging the surrounding blood cells for navigation. However, the most effective swimming mechanism for propulsion in blood remains unknown. In this study, we numerically investigate two different microrobots: 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. When the microrobot size is comparable to a red blood cell, the puller microrobot swims faster than the pusher microrobot. When the microrobot size becomes much smaller, on the other hand, the pusher microrobot swims faster than the puller microrobot. The swimming speed is thus strongly dependent on the swimmer type and microrobot size as well as hematocrit and magnetic torque used to control the microrobot orientation. These results offer valuable insights into the design of microrobots that can efficiently navigate through blood, with implications for targeted drug delivery and minimally invasive medical procedures.