Abstract Alginate-based magnetic micro/millirobots have demonstrated significant potential for biomedical applications due to their flexible structures and capacity to carry various types of cargo, such as cells, enabling targeted therapy to specific diseased regions within the body. Their active therapy is typically achieved through magnetic actuation and magnetic heating, while monitored by medical imaging methods like CT which pose additional risks due to radiation exposure. In the last decades, a novel imaging method for superparamagnetic materials, known as magnetic particle imaging (MPI), has been under active development, offering not only positional tracking but also the ability to measure concentration and temperature. Here, we report the world’s first MPI-traceable magnetic hydrogel robots, which employ a combination of iron oxide nanoflowers, NdFeB powder, and calcium alginate. Unlike previous magnetic alginate robots composed of a single magnetic material, the synergistic combination of NdFeB and nanoflowers enables these robots to exhibit triple magnetic functionalities: magnetic heating, locomotion at low magnetic fields, and tracking, all of which can be controlled using a single all-in-one electromagnetic coil system. The effects of various magnetization fields, as well as different concentrations of NdFeB and nanoflowers on the robots’ magnetic properties were analyzed. This led to the development of three types of triple-function robots (spiral, droplet, and hybrid), with experimental results demonstrating biocompatibility, a magnetic heating temperature increase of over 10 ºC in plasma fluid under a magnetic field of 13 kA·m ‒1 at 200 kHz, locomotion speeds of up to 25 mm·s ‒1 in fields below 2 mT, and an MPI tracking error of 2.8 mm with a selection field of 0.4 mT·mm ‒1 . Additionally, the robots’ capacity for localized thermal therapy and selectively targeted cell delivery, as well as their locomotion within a medical phantom against a maximum flow of 50 mm·s ‒1 were demonstrated.

Magnetic microrobots can be miniaturized to a nanometric scale owing to their wireless actuation, thereby rendering them ideal for numerous biomedical applications. As a result, nowadays, there exist several mechano-electromagnetic systems for their actuation. However, magnetic actuation is not sufficient for implementation in biomedical applications, and further functionalities such as imaging and heating are required. This study proposes a multimodal electromagnetic system comprised of three pairs of Helmholtz coils, a pair of Maxwell coils, and a high-frequency solenoid to realize multimodal locomotion and heating control of magnetic microrobots. The system produces different configurations of magnetic fields that can generate magnetic forces and torques for the multimodal locomotion of magnetic microrobots, as well as generate magnetic traps that can control the locomotion of magnetic swarms. Furthermore, these magnetic fields are employed to control the magnetization of magnetic nanoparticles, affecting their magnetic relaxation mechanisms and diminishing their thermal properties. Thus, the system enables the control of the temperature increase of soft-magnetic materials and selective heating of magnetic microrobots at different positions, while suppressing the heating properties of magnetic nanoparticles located at undesired areas.