Development and Degradation Study of PLA-Based Medical Implant Markers for Magnetic Particle Imaging

Magnetic particle imaging (MPI) is a promising imaging modality nearing clinical introduction. MPI's tracer-based principle allows for highly sensitive background-free imaging. Potential clinical applications include cardiovascular imaging and endovascular interventions. In principle, medical instruments are invisible in MPI due to the missing signal generation. Therefore, permanent marking technologies have been introduced. Additionally, temporary markers are of interest for follow-up examinations after stent implantation to prevent artifacts during postinterventional stent lumen quantification. Consequently, medical instrument markers for MPI, based on biodegradable polylactic acid (PLA) and superparamagnetic iron-oxide nanoparticles (SPIONs), are developed in this study. To investigate the markers, signal characteristics and degradation over time are studied for 28 d in a water bath at 37 °C. The samples are analyzed using a scale, micro-CT, microscopy, magnetic particle spectroscopy (MPS), MPI, and vibrating sample magnetometry (VSM). A continuous mass decrease is detected (≈90% after 28 d), while MPS and MPI data show no loss of signal. VSM confirms that the markers' mass reduction can be accounted for the degradation of PLA, while the SPIONs hardly detach from the coating. The introduced marking technology, with its degradation characteristics and signal behavior, is the basis for a variety of anticipated medical application scenarios.