Collective methods of propulsion and steering for untethered microscale nanorobots navigating in the human vascular network

In the field of medical nanorobotics, nanometre-scale components and phenomena are exploited within the context of robotics to provide new medical diagnostic and interventional procedures, or at least to enhance the existing ones. The best route for such miniature robots to access various regions inside the human body is certainly the vascular network. Such a network is made of nearly 100 000km of blood vessels varying in diameters from a few millimetres in the arteries down to similar to 4 mu m the capillaries with respective important variations in blood flow velocities. When injected in the blood circulatory network using existing modern techniques such as catheterization, such robots must travel from larger-diameter vessels before reaching much tinier capillaries. As such, the use of a single type of microscale robots capable of travelling in various environments and conditions related to such different blood vessels while being trackable by an external system seems, at the present time, inconceivable. Therefore, as explained in this article, an approach based on the use of several types of microscale robots with complementary methods of propulsion and steering capable of operating in a collective manner is more likely to achieve better results. This is especially true for interventions such as direct tumour targeting where the tiniest blood vessels such as the ones found in the angiogenesis network must be travelled.