Closed‐Loop Control Characterization of Untethered Small‐Scale Helical Device in Physiological Fluid with Dynamic Flow Rates

Untethered small-scale helical devices (USHDs) have the potential to navigate blood vessels and treat vascular occlusive diseases. However, there are still many challenges in translating this method into clinical practice, both in terms of localization and wireless motion control. Herein, closed-loop control characterization of the USHD against and along physiological fluid inside a blood vessel phantom at different penetration depths is shown. First the dynamic flow and ultrasound images noise affecting the measurement are modeled, and control system of the USHD based on bifurcation analysis of a 1D hydrodynamic model is designed. Then a region of attraction of a USHD driven by a permanent magnet robotic (PMR) system inside a blood vessel phantom around an equilibrium point is constructed. Further, the point-to-point closed-loop control strategy is implemented based on the magnetic point-dipole approximation and kinematic control of the PMR system and ultrasound feedback inside physiological fluid, blood vessel, and soft tissue. The frequency response of the USHD is characterized against and along the flowing streams of fetal bovine serum within different flow rates in the 6-20 mm s(-1) range. The experimental results demonstrate the ability to navigate the USHD inside blood vessel phantoms with maximum position error of 1.99 +/- 0.55 mm.