Recent strides in the development of untethered miniature robots have shown the advantages of diverse actuation methods, flexible maneuverability, and precise locomotion control, which has made miniature robots attractive for biomedical applications such as drug delivery, minimally invasive surgery, and disease diagnosis. However, biocompatibility and environmental adaptability are among the challenges for further in vivo applications of miniature robots due to the sophisticated physiological environment. Herein, we propose a biodegradable magnetic hydrogel robot (BMHR) that possesses precise locomotion with four stable motion modes, namely tumbling mode, precession mode, spinning-XY mode, and spinning-Z mode. Using a homemade vision-guided magnetic driving system, the BMHR can achieve flexible conversion between the different motion modes to cope with changes in complex environments, and its superior ability to cross obstacles is demonstrated. In addition, the transformation mechanism between different motion modes is analyzed and simulated. Benefiting from the diverse motion modes, the proposed BMHR has promising applications in drug delivery, showing remarkable effectiveness in targeted cargo delivery. The BMHR's biocompatible property, multimodal locomotion, and functionality with drug-loaded particles can provide a new perspective to combine miniature robots with biomedical applications.
Keywords: biodegradable material; electromagnetic actuation; magnetic hydrogel robot; multimodal locomotion; targeted cargo delivery.