Development of a Local Magnetic Actuation System for Precise Microrobotic Cargo Manipulation in Biomedical Applications

Magnetic field-driven systems have shown great potential in biomedical applications such as targeted drug delivery, imaging and magnetic hyperthermia. Magnetic methods enable wireless manipulation while being harmless to the human body. In particular, magnetic microrobots are gaining attention due to their potential to access hard-to-reach regions of the body while remaining remotely controllable. At the same time, external remote, i.e., global, magnetic control is highly limited, resulting in magnetic agents’ loss on the way to a target position. Alternatively, a multi-robot distributed control approach can be put in place. An untethered or tethered milli-scale carrier can leverage a larger volume for performing most of the path and can be used to release microrobots closer to a target position and to provide local control inputs to the released cargo. To cope with this challenge, this thesis presents a local magnetic control strategy for the manipulation of released magnetic microrobotic cargo. The system relies on millimetre-sized coils, arranged around a milli-scale robotic carrier, capable of generating spatio-temporally varying magnetic fields and gradients up to 15 mT and 9 T/m, respectively, in the near coil region. A real-time control interface was developed to control the current through the coils, creating different control modes, such as particle trapping and vortex-like swarm formation, both enabling active post-release control of the cargo. To predict the feasibility of microrobot manipulation, an analytical model was developed. The dynamic model aims to simulate the behaviour of the microrobots in a medium under applied fields and gradients. The computed forces exerted by the coils in a given position and orientation were combined with the gravity and the drag forces acting on the microrobots, here simulated as magnetic particles. As an output, the model could predict the percentage of controllable particles in a three-dimensional region. In addition to this, dynamic components could be computed, such as particle trajectories and attraction time to a coil. The model was then qualitatively validated, comparing it with the experimental part results given by the tests with the actuation system developed. The proposed approach provides a novel local manipulation system for magnetic microparticles and suggests a pathway toward in situ positioning of a therapeutic cargo.