Biomedical applications

Wang, T., Ugurlu, H., Yan, Y., Li, M., Li, M., Wild, A.M., Yildiz, E., Schneider, M., Sheehan, D., Hu, W. and Sitti, M., 2022. Adaptive wireless millirobotic locomotion into distal vasculature. Nature Communications, 13(1), pp.1-17.

Microcatheters have enabled diverse minimally invasive endovascular operations and notable health benefits compared with open surgeries. However, with tortuous routes far from the arterial puncture site, the distal vascular regions remain challenging for safe catheter access. Therefore, we propose a wireless stent-shaped magnetic soft robot to be deployed, actively navigated, used for medical functions, and retrieved in the example M4 segment of the middle cerebral artery. We investigate shape-adaptively controlled locomotion in phantoms emulating the physiological conditions here, where the lumen diameter shrinks from 1.5 mm to 1 mm, the radius of curvature of the tortuous lumen gets as small as 3 mm, the lumen bifurcation angle goes up to 120°, and the pulsatile flow speed reaches up to 26 cm/s. The robot can also withstand the flow when the magnetic actuation is turned off. These locomotion capabilities are confirmed in porcine arteries ex vivo. Furthermore, variants of the robot could release the tissue plasminogen activator on-demand locally for thrombolysis and function as flow diverters, initiating promising therapies towards acute ischemic stroke, aneurysm, arteriovenous malformation, dural arteriovenous fistulas, and brain tumors. These functions should facilitate the robot’s usage in new distal endovascular operations.

Yan, Y.*, Wang, T.*, Zhang, R., Liu, Y., Hu, W. and Sitti, M., 2023. Magnetically assisted soft milli-tools for occluded lumen morphology detection. Science Advances, 9(33), p.eadi3979.

Methodologies based on intravascular imaging have revolutionized the diagnosis and treatment of endovascular diseases. However, current methods are limited in detecting, i.e., visualizing and crossing, complicated occluded vessels. Therefore, we propose a miniature soft tool comprising a magnet-assisted active deformation segment (ADS) and a fluid drag-driven segment (FDS) to visualize and cross the occlusions with various morphologies. First, via soft-bodied deformation and interaction, the ADS could visualize the structure details of partial occlusions with features as small as 0.5 millimeters. Then, by leveraging the fluidic drag from the pulsatile flow, the FDS could automatically detect an entry point selectively from severe occlusions with complicated microchannels whose diameters are down to 0.2 millimeters. The functions have been validated in both biologically relevant phantoms and organs ex vivo. This soft tool could help enhance the efficacy of minimally invasive medicine for the diagnosis and treatment of occlusions in various circulatory systems.

Wang, T., Hu, W., Ren, Z. and Sitti, M., 2020. Ultrasound-guided wireless tubular robotic anchoring system. IEEE Robotics and Automation Letters, 5(3), pp.4859-4866.

Untethered miniature robots have shown great potential in biomedical diagnoses and surgeries. For applications such as drug delivery and physical contraception inside tubular structures, it is desirable to have a miniature anchoring robot with a self-locking mechanism at the target in vivo region. Moreover, the behavior of this robot should be tracked and controlled by a medical imaging-based system. While such a system is unavailable, we report a reversible untethered anchoring robot design based on magnetic actuation. The current robot's dimension is 7.5 mm × 17.8 mm and is made of soft polyurethane elastomer, photopolymer, and permanent magnets. Its relaxation and anchoring states can be maintained in a stable manner without supplying control input. To control the robot's locomotion, we implement an ultrasound imaging-based tracking and control system, to automatically sweep locally and update the robot position measurement. With such a system, we demonstrate that the robot can be controlled to follow a pre-defined path with the maximal position error of 0.53 ± 0.05 mm inside a tubular phantom, where the reversible anchoring could be achieved under the monitoring of ultrasound imaging.