Biomembrane-inspired design of medical micro/nanorobots: From cytomembrane stealth cloaks to cellularized Trojan horses

Micro/nanorobots are promising for a wide range of biomedical applications (such as targeted tumor, thrombus, and infection therapies in hard-to-reach body sites) because of their tiny size and high maneuverability through the actuation of external fields (e.g., magnetic field, light, ultrasound, electric field, and/or heat). However, fully synthetic micro/nanorobots as foreign objects are susceptible to phagocytosis and clearance by diverse phagocytes. To address this issue, researchers have attempted to develop various cytomembrane-camouflaged micro/nanorobots by two means: (1) direct coating of micro/nanorobots with cytomembranes derived from living cells and (2) the swallowing of micro/nanorobots by living immunocytes via phagocytosis. The camouflaging with cytomembranes or living immunocytes not only protects micro/nanorobots from phagocytosis, but also endows them with new characteristics or functionalities, such as prolonging propulsion in biofluids, targeting diseased areas, or neutralizing bacterial toxins. In this review, we comprehensively summarize the recent advances and developments of cytomembrane-camouflaged medical micro/nanorobots. We first discuss how cytomembrane coating nanotechnology has been employed to engineer synthetic nanomaterials, and then we review in detail how cytomembrane camouflage tactic can be exploited to functionalize micro/nanorobots. We aim to bridge the gap between cytomembrane-cloaked micro/nanorobots and nanomaterials and to provide design guidance for developing cytomembrane-camouflaged micro/nanorobots.