Magnetic forces induce cell condensation necessary for stem cell differentiation into cartilage and elicit the formation of a tissue-like structure: Magnetically driven fusion of aggregates assembled by micromagnets results in the formation of a continuous tissue layer containing abundant cartilage matrix.

We demonstrate a facile approach to design three-dimensional cellular assembly of tunable size and controlled geometry with applications for tissue engineering. Three-dimensional cell patterning was performed using external magnetic forces, without the need for substrate chemical or physical modifications. Human endothelial progenitor cells and mouse macrophages were magnetically labeled using anionic citrate-coated iron oxide nanoparticles. Two magnetic tips were designed, and their magnetic field cartographies were calibrated. The focalized magnetic force generated ensured an efficient entrapment of the cells at the tips vicinity. By tuning the magnetic field gradient geometry and intensity, the magnetic cellular load, and the number of cells, we fully described the formation of the three-dimensional multicellular assemblies, and estimated the corresponding packing factor for a large range of experimental conditions.