Ultrasound Doppler Imaging and Navigation of Collective Magnetic Cell Microrobots in Blood

We propose ultrasound Doppler imaging and magnetic navigation of collective cell microrobots in whole blood. Cell microrobots are cultured using stem cells and iron microparticles, they have spheroidal structures and can be actuated under external magnetic fields. A collective of cell microrobots can be reversibly gathered and spread due to the tunable magnetic interaction, and are able to exhibit collective motion in whole blood under rotating magnetic fields. Simulation results indicate that the induced blood flow around the collective pattern affects the motion of red blood cells (RBCs), and experimental results show that Doppler signals are observed when emitting ultrasound waves to the microrobots. The induced Doppler signals are affected by the input field frequency and the ultrasound parameters (pulse repetition frequency). Due to the induced three-dimensional blood flow, Doppler signals can be observed when the imaging plane is above the collective microrobots, which enables indirect localization when performing navigation on an uneven surface. Our study investigates a strategy for pattern formation and navigation of collective microrobots under ultrasound Doppler imaging, demonstrating that the integration of collective control approach and medical imaging holds great potential for real-time active delivery tasks.