Magnetic helical micro-/nanomachines: Recent progress and perspective

Inspired by bacterial flagella, helical micro-/nanomachines (H-MNMs) can achieve controllable 3D movement by converting rotational motion to translation in a corkscrew fashion. Because they can be operated efficiently in narrow and confined spaces, functionalized with active components, and propelled by a magnetic field that does not harm tissue, H-MNMs have been extensively investigated to perform various biomedical tasks. Over the past decade of H-MNM development, significant research progress has been achieved, including cell stimulation, overcoming of biological barriers, targeted drug delivery, and imaging/tracking in vivo. This progress was enabled by the employment of new materials, structural designs, and functions. In this review, we summarize the latest developments of H-MNMs with a focus on their functionalization and key breakthroughs for biomedical applications. We also discuss the main challenges and future research directions to be undertaken to further advance these tiny corkscrew-like machines toward translational medicine and minimally invasive interventions.