Digital Theses Archive


Tesi etd-11292022-182859

Type of thesis
Novel Magnetic Technologies For Endovascular Applications
Scientific disciplinary sector
Istituto di Biorobotica - BIOROBOTICS
relatore Prof.ssa MENCIASSI, ARIANNA
Membro Prof.ssa DANKELMAN, JENNY
  • magnetic
  • actuation
  • composites
  • 3D printing
  • EM coils
  • anisotropy
  • catheter
  • cannulation
  • endovascular
  • robotic
Exam session start date
Traditional surgical procedures to treat coronary diseases are highly invasive and carry with them a high risk of morbidity. In contrast, minimally invasive procedures are as efficient as traditional surgical methods while being safer. Therefore, the use of catheters is becoming increasingly common in surgical procedures. However, working with traditional catheters and guidewires requires extensive skill and experience on the surgeon’s part as they lack active tip steering. With greater operator experience and skills, the success rate of endoluminal catheterization procedures goes higher. To offset this need for skill and experience, robotic approaches and steerable catheters are proposed.<br><br>Robotic approaches help in improving catheter navigation to bypass anomalies and prevent tissue damage. While robotic approaches achieve good navigation precision and accuracy, they suffer from high cost. There is also a setup time for the system before each procedure and additional staff training is necessary. On the other hand, the use of steerable catheters involves significantly lower cost and setup time while helping the surgeon with navigation and control. In light of their ability to easily deform and adapt to the environment, soft materials are particularly attractive when targeting medical applications. To actuate soft materials, remote magnetic actuation is uniquely suited for this task due to its safety, controllability, and miniaturization capabilities. Among the magnetically actuated catheters reported in literature, it was found that instead of embedding discrete permanent magnets in the catheter, it is more beneficial to have uniformly distributed magnetic microparticles throughout their entire body. Controlling the direction of magnetization of the magnetic microparticles in the magnetic catheter or other soft magnetic structures gives the liberty to program the way they get actuated in a magnetic field. A novel fabrication paradigm that can combine and exploit the benefits of 3D printing and control of the structure’s magnetization is reported in this thesis. However, incorporating such magnetic anisotropy into their body is not straightforward. Here, we demonstrated a 3D printing method allowing to incorporate magnetic anisotropy directly into the printed soft structure. This offers at the same time a simple and time-efficient magnetic soft robot prototyping strategy. The proposed process involved orienting the magnetized particles in the magnetic ink used in the 3D printer, by a custom electromagnetic coil system acting onto the particles while printing. The resulting structures were extensively characterized to confirm the validity of the process. The extent of orientation was determined to be between 92% and 99%. A few examples of remotely actuated small-scale soft robots that were printed through our method are also demonstrated. Just like 3D printing gives the freedom to print a large number of variations in shapes, the proposed method also gives the freedom to incorporate an extensive range of magnetic anisotropy.<br><br>As far as the author is aware of, this work shows the first hollow soft magnetic catheter tip for targeting the coronary arteries fabricated using the developed 3D printing method. A hollow catheter gives the ability to introduce guidewires and other functionalities through it which may be needed during the surgery. An External Permanent Magnet (EPM) that can be mounted on a robotic arm was used to actuate the fabricated magnetic catheter. The catheter was characterized in detail in terms of its bending hysteresis, bending forces, and dynamic response. The catheter showed &lt;10% hysteresis on average and bending forces up to 0.8N. The magnetic catheter was then successfully guided (5 out of 6 times) using the EPM mounted on a robotic arm inside a realistic aortic phantom while being inserted using a robotic catheter driver. Each such successful trial took 100s.<br><br>Further, this concept was extended to be used in a robot-assisted catheterization platform. In conjunction with a larger base catheter that can anchor itself in the aorta and guide the magnetic catheters from it, 100% (10 trials) successful catheterization was achieved from certain anchor points in the aorta. Regions from which it was not feasible to perform successful catheterizations were also identified. The developed procedure in this thesis could be extended to other endovascular applications as well.<br><br>While catheters consisting discrete permanent magnets are not well suited for navigating through narrow lumen of the body, they are very well suited for filtering and retrieving therapeutic magnetic nanoparticles from the bloodstream. A nanoparticle retrieval catheter concept containing a magnetic module is presented. A high capture efficiency (50% up to 92%) for a varied particle size (10nm to 500nm) was numerically calculated. The proposed method could be a solution to the oft undiscussed aspect of using magnetic micro- and nanoparticles for therapy inside the body.<br><br>It is hoped that the field of novel magnetic technologies for endovascular applications will be advanced one step forward through this thesis.