Building medical microrobots from the body's own cells may circumvent the biocompatibility concern and hence present more potential in clinical applications to improve the possibility of escaping from the host defense mechanism. More importantly, live cells can enable therapeutically relevant functions significantly more efficiently than synthetic systems. In this direction, living immune cell-derived microrobots from macrophages, immunobots, which can be remotely steered with externally applied magnetic fields and directed toward anti-tumorigenic (M1) phenotypes, were presented [1]. Macrophages engulfed the engineered magnetic nanoparticles, composed of 500 nm diameter silica Janus particles with one side coated with FePt magnetic nanofilm for magnetic steering and medical imaging and bacterial lipopolysaccharides for stimulating macrophages in a tumor-killing state. The torque-based surface rolling locomotion of the immunobots was demonstrated inside blood plasma, over a layer of endothelial cells, and under physiologically relevant flow rates. The immunobots secreted signature M1 cytokines and M1 cell markers via stimulation with bacterial lipopolysaccharides. The immunobots exhibited anticancer activity against urinary bladder cancer cells. Such immunobots were further developed from freshly isolated primary bone marrow-derived macrophages since patient-derivable macrophages have strong clinical potential for future cell therapies in cancer while eliminating side effects and unwanted immune reactions [1].

Next, the immunobots were further investigated using medical imaging modalities, such as magnetic resonance imaging and optoacoustic imaging in soft-tissue-mimicking phantoms and ex vivo conditions. Magnetic actuation and real-time imaging of immunobots were demonstrated under static and physiologically relevant flow conditions using optoacoustic imaging [2]. The proposed approach demonstrated the proof-of-concept feasibility of integrating macrophage-based microrobots into clinic imaging modalities for cancer targeting and intervention, and can also be implemented for various other medical applications.