Scaffold‐free formation of a millimeter‐scale multicellular spheroid with an internal cavity from magnetically levitated 3T3 cells that ingested iron oxide‐containing microspheres

This report describes fabrication of a millimeter‐scale three‐dimensional (3D) multicellular structure with a central cavity based on magnetic levitation of 3T3 cells that had ingested Fe 3 O 4 ‐containing microcapsules. Magnetically levitated cells initially formed a disc‐shaped cell cluster at the air‐medium interface and transformed into a spheroid (up to 2.8 mm in diameter) after 10‐day incubation under a magnet. Hematoxylin‐and‐eosin‐stained section revealed that an eosinophilic shell of cells enclosed a pale‐staining core of the spheroid. Mitotic or elongated and aligned cells were found at the outer periphery of the shell, while Fe 3 O 4 deposits were distributed in the inner part of the shell. Surgical dissection indicated that the spheroid had a hollow interior filled with a fluid‐state cell suspension. Accordingly, it was demonstrated that magnetically levitated 3T3 cells organized themselves into a tissue‐like spheroid, resulting in core cell death. The spheroid can be used as a 3D tissue model and as building blocks that fused to form a more complicated structure. Biotechnol. Biotechnol. Bioeng. 2014;111: 1038–1047. © 2013 Wiley Periodicals, Inc.