Physikalisch-Technische Bundesanstalt 1 article published in JoVE Medicine Preparation and In Vitro Characterization of Magnetized miR-modified Endothelial Cells Natalia Voronina1, Heiko Lemcke1, Frank Wiekhorst2, Jens-Peter Kühn3, Markus Frank4, Gustav Steinhoff1, Robert David1 1Reference and Translation Center for Cardiac Stem Cell Therapy (RTC), Department of Cardiac Surgery, University of Rostock, 2Physikalisch-Technische Bundesanstalt, 3Department of Radiology and Neuroradiology, Ernst-Moritz-Arndt-University Greifswald, 4Electron Microscopy Center, University of Rostock This manuscript describes the efficient, non-viral delivery of miR to endothelial cells by a PEI/MNP vector and their magnetization. Thus, in addition to genetic modification, this approach allows for magnetic cell guidance and MRI detectability. The technique can be used to improve the characteristics of therapeutic cell products.