Engineering Automated Microrobotic Systems with Machine Learning-Based Control for Biomedical Applications

For many diseases and injuries, the pathological effects are local to particular areas of the body. In such cases, systemic drug delivery is nonideal treatment because drugs used to treat the pathological condition may have a deleterious effect on the remaining healthy tissue and cause damaging side effects. A similar kind of harm is done in many surgical scenarios when healthy tissue must be cut in order to give the surgeon physical access to the damaged tissue underneath. There exists an unmet clinical need to be able to deliver minimally invasive therapeutic interventions precisely within the body, while minimizing harm to healthy tissue. Towards this end, we are developing swimming microrobotic systems to traverse the fluidic pathways within the body, in order to deliver locally targeted therapeutic payloads noninvasively, and with precision, to areas which are difficult to access noninvasively using current methods. In this dissertation, I present a control approach which uses machine learning in order to develop robust control policies for magnetically actuated microrobots navigating within small scale fluidic environments. We have developed a controller for a helical magnetic hydrogel microrobot that uses the soft actor critic reinforcement learning algorithm to autonomously derive control policies which allow the microrobot to swim through an uncharacterized biomimetic fluidic environment, actuated by time varying magnetic fields generated from a three-axis array of electromagnets. Our results show that this model-free control approach can learn and adapt to the dynamic features of the microrobot, the fluidic environment, and the electromagnetic actuator in order to successfully accomplish navigation tasks. Additionally, we demonstrate that the control policies learned by the reinforcement learning algorithm repeatedly converge to recapitulate the behavior of rationally designed controllers based on physical models of helical swimming microrobots. We also present an approach for developing biohybrid magnetic microrobots with chemical sensing capabilities based on genetically encoded surface chemistry, and explore hydrogel based magnetic microrobots as vehicles for antibiotic delivery. Together, these contributions form a suite of microrobotic technologies for autonomous navigation, sensing, and localized drug delivery within small scale fluidic environments, and are an important step towards clinical applications of microrobotic technology