Recent advances in engineering nano/ microrobots for tumor treatment

Until now, although nanomedicines have gained much success in tumor treatment by reducing severe toxic side effects of drugs and improving the therapeutic efficiency of drugs, they are still faced with thorny challenges in targeted drug delivery including insufficient targeting accuracy, poor penetration into tumor core, and systemic toxicity issues. Recently, engineering nano/microrobots with multiple remarkable properties such as real-time sensing, interacting and manipulating capabilities, and programmability, have received increasing attention in biomedical applications ranging from disease diagnosis, targeted drug delivery, medical imaging, and surgery. More importantly, in different driven modes, nano/microrobots are capable of performing a wide variety of powerful functions, such as enhancing tissue penetration and payload retention in deep-seated tumors with active navigation, being programmable to release drugs or performing specific tasks directly at the tumor site with high precision and accuracy, automating repeated tumor treatment without the need for frequent interventions, and minimizing out-of-target tissue damage, leading to a huge exploration potential in tumor treatment. In this review, we delve into the recent progress and the development direction of nano/microrobots for tumor treatment and emphasize the working mechanisms and the unique functionalities of different driven modes in detail. Meanwhile, we elaborate on the application of nano/microrobots fabricated from various types of materials in tumor therapy. Finally, the key factors to be considered in the clinical translation of the above nano/microrobots are proposed.