Microscale hydrogel-based computer-triggered polymorphic microrobots for operations in the vascular network

A new type of microrobots for medical interventions in the vascular network is presented. In its simplest form, each microscale robots consists of magnetic nanoparticles (MNP) embedded in a thermo-sensitive hydrogel, also known as PNIPA. The nanoparticles are not only used for propulsion/steering, and MRI-based tracking inside the body due to local magnetic field inhomogeneity, but also for triggering a change of volume of the microrobots. The latter is possible since the MNP can introduce heat in the hydrogel-based microrobots when placed in an AC magnetic field. In this paper, spherical PNIPA-MNP were synthesized and propelled by the magnetic gradient field inside a clinical MRI scanner before being submitted when at a targeted location to a special apparatus capable of generating an AC magnetic field of 4 kA.m^-1 at 160 kHz. Temperature elevations and change in the overall volume of the microrobots were recorded.