Micro- and nanorobots for intelligent bone tissue engineering

The repair of bone defects presents a significant challenge in balancing material properties with biocompatibility. While traditional materials such as alloys are widely used, they still exhibit limitations in mechanical adaptability, osseointegration capacity, and imaging interference. In recent years, the integration of biodegradable materials and 3D printing technology has provided novel approaches for personalized bone repair, however, the implantation of these scaffolds often requires open surgery, which causes pain for patients, increases the risk of infection, and prolongs healing time. In this context, the micro- and nanorobots (MNRs) can offer groundbreaking opportunities for precision bone tissue engineering in a minimally invasive or even non-invasive manner owing to their unique advantages such as tiny size, precise delivery, and dynamic modulation capabilities. This article focuses on the application potential of MNRs in bone repair, systematically examining their design prerequisites: achieving targeted movement within the tubular structures (such as blood vessels and lymph vessels), cavity structures (such as marrow cavity and articular cavity), and defect space (such as fractures and osteoporosis) in the bone tissue, and analyzing their material selection, propulsion mechanisms, and real-time monitoring strategies. Furthermore, we review recent advances in MNRs-assisted bone defect regeneration, bone infection control, and bone tumor therapy, highlighting their advantages in modulating the local bone microenvironment through the delivery of growth factors, stem cells, or therapeutic agents. Finally, we summarize current technological bottlenecks and propose interdisciplinary solutions to address these challenges. The prospects of MNRs in dynamic repair and regenerative medicine are also discussed. Our goal is to provide a comprehensive reference and offer guidance for rationally designing versatile MNRs for advanced bone tissue engineering, thereby bridging the gap between tiny active MNRs and traditional bone tissue engineering by making full use of the anatomical structures of healthy bones and the abnormal structures of diseased or injured bones.