Untethered microrobots (UMRs) propelled by multiple external power sources have emerged as promising tools for biomedical applications, such as targeted cargo delivery (TCD), microsurgery, thrombolysis, medical imaging, etc. In particular, owing to their minimal invasiveness and capability of accessing hard‐to‐reach regions of the human body in a controllable manner, the application of UMRs for TCD is of great interest in recent years. Here, the state‐of‐the‐art UMRs in this regard are presented, focused on targeted drug and cell delivery systems. Meanwhile, this review systematically details recent research studies on the use of UMRs in TCD, containing their constituent materials (functional, scaffold, and smart materials), fabrication methods, and three types of external propulsion energy sources concerning their mechanisms and corresponding typical designs. Subsequently, various strategies for controlled drug release are summarized, as well as the latest targeted cell delivery systems and relevant cell manipulation in vitro or in ex vivo. Finally, the current challenges to clinical translation faced by the UMRs and future perspectives on this field are highlighted.

Untethered biocompatible microswimmers driven by micromotors in fluids can enable innovative technologies in fields such as biology and chemical and biomedical engineering. However, efficiently driving and controlling the movement of microswimmers by light remains a challenge. Herein, a method for fabricating a light‐driven microswimmer with built‐in micromotors and 3D‐printed multiscale features that exhibits high photocatalytic performance is proposed. TiO2‐CaCO3 composite microparticles (TC) are fabricated as highly efficient micromotors that provide high photocatalytic efficiency in bubble generation, while 3D‐printed hydrogels are fabricated as TiO2‐CaCO3/PEGDA (TC/P) microswimmers that provide biocompatibility, large specific surface area, and controllable movement. The results show that TC micromotors produced by physical mixing at a specific concentration exhibit a large specific surface area, reduced agglomeration, increased photocatalytic active sites, and improved photocatalytic stability. TC micromotors are effectively loaded into the porous hydrogel by 3D printing for multiscale fabrication to improve the photocatalytic performance across scales and realize effective and directional driving under violet light excitation. The TC/P microswimmers exhibit stable catalysis and motion in 7 days, at which point the catalysis by TiO2 is already ineffective. With stability, biocompatibility, and biomedical functions, this multiscale fabricated microswimmer exhibits great potential in micromanipulation and targeted therapy.

Microrobots have been extensively studied for biomedical applications, and significant innovations and advances have been made in diverse aspects of the field. However, most studies have been based on individual...

Untethered synthetic microrobots have significant potential to revolutionize biomedical interventions therapy in the future. However, the relatively slow speed of microrobots and viscosity biofluid environments are some of barriers standing in the way of microrobots’ biomedical applications. Herein, inspired by high‐speed biological escape propulsion, NIR‐driven microrobots with a high‐speed, unidirectional propulsion in the high‐viscosity liquid are proposed. The bubble's growth and ejection cause the proposed 3D‐printed microrobot to propel forward. The 3D‐printed claw‐like microrobot achieves motion average speed of 1.4 mm s−1 (three‐body length (bl) s−1) when driven by NIR light in a pure glycerol viscous (945 mPa s, 25 °C) environment, which has a viscosity that is more than 200 times the viscosity of blood and of 54 mm s−1 (120 bl s−1) when driven by NIR light in deionized (DI) water. This work provides more ideas for the design and propulsion of light‐driven microrobots in a high‐viscosity vivo environment, which may broaden the applications of microrobots in the biomedical field, such as propulsion and navigation in confined and hard‐to‐reach body location areas.

A microsystem composed of multiple rotating micromotors can achieve reversible transformation between cooperative and interactive modes, and dynamic behaviours of self-organization are realized based on the microsystem.