Intracorporeal anchoring and guiding system with permanent magnet force modulation

Magnetic manipulation of objects within the body is a growing field of research since the second half of the last century. Therapeutic and diagnostic capabilities offered by such technology are extended with the clinical need to make procedures less invasive and traumatic for the patients. Ophthalmologists were among the first to explore magnetic manipulation for removing iron fragments from the interior of the eye. Subsequently, the intubation devices were developed for extracting foreign objects from the body. The first case of magnetic guidance is an intravascular catheter magnetically guided by large external magnets in the 1950s. Half a century later, magnetic actuation of medical devices has led to many developments growing in complexity, such as wireless endoscopic capsule for exploring the gastrointestinal tract; intraocular microrobots of sub-millimitric size per- forming delicate tasks; internal magnetic laparoscopic instruments magnetically coupled through the abdominal wall without the need of additional incisions; or enormous systems for remote magnetic steering of catheters in cardiovascular or neurological procedures. Technically, magnetic guidance requires variable, reshapable or steerable magnetic fields and therefore is generally associated with large magnetic arrangements of coils or perma- nent magnets surrounding the patient; while magnetic anchoring is achievable by external permanent magnets of adequate size placed or dragged manually on the surface of the body. In this thesis work, we propose a novel type of magnetic guidance. Instead of having the guiding part external to the body, we propose to perform the guidance locally, on- site, by having the guiding part within the body in close vicinity of the element to be guided. Although the separation distance between the guiding and guided member is decreased, the required magnetic field to be generated is still significant with regards to the size of the system. Moreover, the magnetic attractions force should be adjusted in order to provide a robust guidance over variable and dynamic anatomical conditions. Electromagnets are an ideal solution by their ability to control the strength, polarity and shape of the generated magnetic field. However, obtaining a substantial magnetic field strength becomes challenging in the millimetric scale. Rare-earth magnets produce strong magnetic fields and become interesting when size is limited. But, they produce a constant field and the resulting attractive forces are strongly depending on the distance, which can be a safety issue. To overcome these hurdles, we present a proof-of-concept of intracorporeal force mod- ulation with steerable permanent magnets. We demonstrate through several examples that the magnetic forces applied to the guided element can be modulated by combining permanent magnets together or with other ferromagnetic materials. A first prototype of force modulator is produced, characterized and tested in vitro. We analyze the behavior of this “magnetotractive” system of guidance through two operating modes, namely passive and active guidance modes. While the passive guidance mode uses static magnetic fields, the active guidance mode allows the variation of the magnetic field during the guidance. Operating at static magnetic field implies that the coupling force within the system depends on the tissue thickness and irregularities. As the coupling force decreases approximately as the square of the distance, levels of coupling force could rapidly change during the guidance. Therefore, having the capability of adjusting the coupling force provides flexibility of the method. We demonstrate that active control can be achieved by a combination of several movable permanent magnets. This provides smoother guidance and superior robustness in comparison with the passive mode. On the guided element, we empirically identify the parameters representing the most significant effect on friction during the guidance. These findings could be very helpful in the design of magnetic guidance systems. Finally, we show that magnetic attractive forces applied on the guided element could be adjusted with permanent magnet arrangements. This solution not only offers larger amplitude of force with regards to its size, but the range of modulation is significant in comparison with electromagnets. In addition, we demonstrate in vitro that intracorporeal magnetic guidance with steerable permanent magnets is feasible over variable and irregular tissue thickness. Therefore, this novel type of guidance has the potential to facilitate for example the treatment of cardiac arrhythmias.