Hyperthermie und Bildgebung von hybriden Polymerfasern und Stents mit inkorporierten magnetischen Nanopartikeln für den medizinischen Einsatz

• Hyperthermia and imaging of hybrid polymer fibers and stents with incorporated magnetic nanoparticles for medical applications

Mues, Benedikt; Fitter, Jörg (Thesis advisor); Slabu, Ioana (Thesis advisor)

1. Auflage. - Göttingen : Cuvillier Verlag (2022)
Book, Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2022

Abstract

Magnetic nanoparticles (MNP) are used as additives in polymers for the development of hybrid stents in order to enable local hyperthermia treatment e. g. for hollow organ tumors. By application of an alternating magnetic field (AMF) a controlled temperature rise in the range of (42-46) °C can be reached, destroying the tumor tissue in close vicinity to the stent. Additionally, the MNP can also be used as contrast agents in magnetic resonance imaging (MRI) or as tracers in magnetic particle imaging, which makes the postoperative visualization of the implanted stent and a monitoring of its function possible. In the manufacturing process of the hybrid stents, the MNP are incorporated in the polymer-matrix. Due to MNP immobilization and occurring MNP agglomerations, a significant impact on the properties of the MNP especially on their magnetic relaxation properties is expected. Since Néel and Brown relaxation influence the performance of the MNP in hyperthermia and imaging, it is necessary to quantify these incorporation induced property changes of the MNP. In this thesis, the influence of the MNP-polymer-matrix interaction on the properties of the incorporated MNP is investigated and the suitability of the hybrid stents in hyperthermia and medical imaging is assessed by means of experimental studies. For that, hybrid stents are made of hybrid melt-spun polypropylene fibers incorporated with different MNP types (core diameters of 10 nm, 100 nm and 400 nm) and different MNP concentrations up to 12 %(m/m). The physicochemical properties, such as distribution and agglomeration state of MNP as well as the static and dynamic magnetic behavior are detected by transmission electron microscopy (TEM), superconducting quantum interference device (SQUID) magnetometry and magnetic particle spectroscopy (MPS). Calorimetric heating measurements as well as MRI and MPI measurements provide insight into the heating power and the imaging performance of the hybrid stents. Compared to the freely dispersed MNP, all MNP incorporated in the polymer-matrix are agglomerated and show higher anisotropy energies and smaller magnetization values caused by interparticle magnetic dipole-dipole interactions. Furthermore, the incorporation of MNP into the polymer leads to a decrease of heating power of up to 80% for Brown-dominated MNP (400 nm) and up to 40% for Néel-dominated MNP (10 nm) at the same AMF parameters (270 kHz, 20 kA/m). The results demonstrate the dependence of the heating power and saturation temperature on AMF parameters (frequency, amplitude), MNP concentration and MNP type. The MPI measurements show high-resolution images for all hybrid fibers, even for those with high MNP concentrations, but the MPI imaging of complex fiber structures such as stents is not possible. MRI measurements produce accurate images of the hybrid stents, especially at the low MNP concentrations. Towards future clinical applications of the hybrid stents, the heating power needs to be tested in already available hyperthermia applicators and the efficacy of hyperthermia needs to be validated in in vitro and in vivo experiments.