Bacteria-based living microrobots may enable targeted delivery of cancer therapeutic agents deep into tumours by exploiting the inherent onboard sensing and self-propulsion of bacteria. In addition, intrinsic or genetically engineered therapeutic functions can be implemented in bacteria — for example, to stimulate an immune response or express therapeutic molecules. However, the innate propulsion of bacteria alone may not be sufficient to ensure targeted delivery, and thus, strategies are needed to bring bacteria efficiently to their intended destinations. Now, writing in Science Robotics, Simone Schuerle and colleagues developed a biohybrid system made of magnetically responsive bacteria and liposomes that act together as controllable living microrobots for targeted drug delivery. Importantly, the researchers have established a magnetic torque-driven control scheme that increases the transport of the microrobots across the endothelial barrier.
Schuerle and colleagues established a hybrid control strategy using rotating magnetic fields (RMFs), which can be generated at clinically relevant scales, to drive magnetotactic bacteria with torques, followed by innate propulsion and autonomous taxis-based navigation. The team developed a model system of vascular endothelium and a three-dimensional spheroid tumour model to study and optimize the parameters of the RMFs in vitro for effective actuation. Notably, the magnetic torque-driven control approach makes the bacteria tumble along blood vessel walls, increasing their probability of passing through the gaps between endothelial cells and entering the tumour tissue. Once in the tumour, the bacteria migrate on their own into hypoxic regions of the tumour.
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