PhD defense – Chuang Li

The defense of the doctoral thesis titled “Advancements in Navigation of Untethered Small-Scale Helical Devices” by Chuang Li was held on Wedensday, 20th of March 2024 at 11:00 am in the Aula of the Academy building of the University of Groningen. The doctoral thesis is available here.

Thesis summary:

Vascular diseases have a profound impact on human health, presenting considerable challenges for patients and healthcare providers alike. These diseases can lead to complications such as arterial blockages, aneurysms, and vascular malformations, which can pose life-threatening risks if not effectively treated. Conventional treatment approaches often involve invasive procedures, which not only carry inherent risks but also entail lengthy recovery periods. With the continuous advancements in science and technology, magnetic helical devices (MHDs) hold great potential as a minimally invasive surgical tool for treating vascular diseases. By combining minimally invasive interventions, precision navigation, real-time imaging, and expanded treatment options, MHDs have the potential to change the field of vascular medicine, improving patient outcomes and reducing the burden associated with vascular diseases. However, numerous challenges persist in the medical applications of MHDs. For instance, the variations in blood flow velocities resulting from different segments of blood vessels or varying diameters of blood vessels can have uncertain effects on the movement and navigation of the MHD inside the circulatory system. As a result, understanding the implications of varying blood flow velocities on motion control of MHDs is paramount for future advancements in medical applications. In addition, blood vessels exhibit heterogeneity in their geometry, diameter, and branching patterns. Navigating through such complex and diverse vascular structures poses challenges in accurately localizing and driving the MHD inside the vascular networks. Hence, it is worthwhile to explore an effective and stable control method that ensures the safety of the human body during motion control of MHDs inside the blood vessel.

The main objective of this doctoral research is the motion control of untethered small-scale helical devices (USHDs) inside blood vessel phantoms with dynamic flow rates. Chapter 1 begins by introducing the development of MHDs, and the medical applications of MHDs, and discusses the challenges in the medical applications. Then the research objectives and the list of publications resulting from this research are then described. Furthermore, we first investigate the helical propulsion of the USHD inside the blood vessel phantom with different flow rates. Chapter 2 presents the region of attraction of a USHD driven by two synchronized rotating permanent magnets inside a fluid-filled lumen around an equilibrium point. The hydrodynamic model of a magnetically-driven USHD is presented, which describes its behavior against the flow of blood serum. Subsequently, the model is validated through 1-D frequency response characterization, demonstrating its ability to capture the measured linear relationship between the actuation frequency and propulsive thrust across different flow fields.

Following the research on the helical propulsion of the USHD, we focus on the investigation of ultrasound-guided closed-loop motion control of the USHD inside a vascular model with a dynamic flow rate. Chapter 3 involves modeling, designing a permanent-magnet robotic (PMR) system, establishing a region of attraction, and implementing a closed-loop control strategy based on ultrasound feedback for the USHD in dynamic flow. Additionally, it demonstrates closed-loop control characterization of the USHD against and along physiological fluid inside a 1-D blood vessel phantom at different penetration depths and a blood vessel phantom with a bifurcation. Different from Chapter 3, Chapter 4 involves the control of the USHD inside a 3-D vascular model that accurately represents anatomical structures. Chapter 4 is also based on ultrasound guidance, the closed-loop motion control of the USHD driven by the PMR system in the 3-D vascular model with dynamic blood flow is performed. First, a 3-D vascular model is constructed by utilizing the 2-D ultrasound images, and waypoints of the 3-D vascular model path are provided as reference paths of the USHD. Next, a control method with robustness is constructed using the PMR system under ultrasound guidance, and the proposed approach is able to drive the USHD through complex and winding paths of the 3-D vascular model to reach the target position. Lastly, this work evaluates the locomotion performance of the USHD inside the 3-D vascular model under various blood flow velocities. This assessment offers insights into the behavior of the USHD under various flow conditions. This contribution also enhances our understanding of the capabilities and limitations of the proposed control method.

To conclude this doctoral thesis, we discuss the results of the three studies conducted in this research, which are covered in Chapters 2-4. Chapter 5 begins by laying out the conclusions and focusing on three key themes: 1) actuation system optimization, 2) biodegradability and safety, 3) ex vivo and in vivo experiments. Finally, directions on future research and an outlook are provided. While the scope of this doctoral research is limited to laboratory experiments, it paves the way for future ex vivo and in vivo experiments. Furthermore, it lays the foundation for future medical applications.



  • Prof. Dr. S. Misra (University of Twente/University of Groningen and University Medical Center Groningen, The Netherlands)


  • Dr. I. S. M. Khalil (University of Twente, The Netherlands)

Assessment Committee

  • Prof. Dr. R. Schirhagl (University of Groningen and University Medical Center Groningen)
  • Prof. Dr. S. Yin (Norwegian University of Science and Technology)
  • Prof. Dr. X. Yang (Harbin Institute of Technology)

Opposition Committee

  • Dr. L. Alic (University of Twente, The Netherlands)
  • Dr. M. A. Shahbazi (University of Groningen and University Medical Center Groningen)
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