Localization of cells using magnetized patterned thin films

In this study, the nasopharyngeal carcinoma cell line was cultured in a superparamagnetic iron oxide nanoparticle aqueous solution with a concentration of 1 μg/mL by using magnetic labeling technology. The cells took up superparamagnetic nanoparticles through the endocytosis process, which caused the cells to become magnetic and manipulable by a magnetic field gradient. Each cell contained 5.266 × 10⁶ superparamagnetic nanoparticles, as determined using the magnetophoresis method. A specific domain configuration and its related distribution of magnetic poles in a patterned thin film were obtained after applying a magnetic field in a specific direction. Here, patterned magnetic thin films were designed to form square grid and square ring structures. When the magnetic field of 3000 G was applied along the diagonal of the square (45° direction) and then released, magnetic cells were trapped at the intersection of the square grid and the 45° diagonal corner of the square ring structure. From micromagnetic simulation results, it was determined that head-to-head and tail-to-tail domain walls with a high magnetic pole density formed at the corners of the square ring structure in the 45° diagonal direction, and the attractive force between a head-to-head/tail-to-tail domain wall and a cell at a height of 1 μm above the corner was approximately 2.055 × 10^-10 N. In the square grid case, the attractive force between the domain wall at the intersection and a cell at a height of 1 μm above the intersection was approximately 2.245 × 10^-10 N. The results of this study demonstrated that cells can simultaneously be arranged at designated locations physically by using patterned magnetic thin films in a noninvasive manner without chemical modification of the substrate.