Figure 1.

Magnetic formation (molding) and compression of CT26 spheroids. (A) Principle of spheroid magnetic molding, depicted with a scheme on the left and photographs on the right. Agarose molds (1 mm) were made using 1 mm magnetic beads (pictures 1 and 2). About 200,000 magnetically labeled CT26 cells were deposited on top of the molds and were attracted and aggregated within them by the cylindrical magnets placed below each mold. Aggregates were then matured overnight (picture 4). Scale bar = 5 mm. (B) Representative pictures of two molded aggregates. On the left, the spheroid was placed on a top of a permanent magnet (MAG+ condition). On the right, the spheroid grew without external stimulation (MAG− condition). For both, time-lapse images are shown. Scale bar = 200 µm. (C) Transmission electron microscopy of MAG+ and MAG− spheroids. The magnetic endosomes of the MAG+ spheroids are aligned along the field gradient, whereas in the MAG− condition, the endosomes containing nanoparticles are homogeneously distributed within the cell cytoplasm. Scale bar = 1 µm. (D) Temporal evolution of the relative height (left panel) and relative volume (right panel) of MAG+ (red curve, n = 9) and MAG− spheroids (black curve, n = 2). The magnetic compression results in a quick decrease in MAG+ relative height (50% after 2 h). The relative volume was stable for the first hour, followed by a slow decrease in the relative volume (25% after a few hours). Both the relative height and volume of the MAG− spheroids increased slowly.