Figure 1: Fabrication of magnetoceptive materials and guided self-assembly of microcomponents.

(a) Microfabrication of cell encapsulating hydrogels via UV photocrosslinking. 50 μl of gel precursor solution was pipetted onto a glass slide, and then, exposed to UV light (500 mW; at a height of 50 mm above the gels) for 20 s. Several types of photomasks with different patterns were employed. (b) Submersion of cell encapsulating hydrogels into stable radical solution for paramagnetization. Inset: Micrographs of fabricated circular, triangular, zig-zag shaped and L-shaped hydrogel units. Scale bar is 1 mm. (c) Guided paramagnetic self-assembly of hydrogels using a permanent NdFeB magnet on a liquid reservoir composed of OptiPrep (20–30 (v/v) %) and Tween-80 (0.001 (v/v) %) in Dulbecco's Phosphate-Buffered Saline (DPBS). Following assembly, a minute amount of precursor solution is ejected onto the assembly. Secondary UV crosslinking was performed to stabilize the overall shape. Vitamin E treatment was applied to switch off the magnetism of assembled hydrogels, which in turn to increase the viability of cells that are encapsulated into hydrogels. (d) Levitational self-assembly of hydrogels in radical solution using two permanent NdFeB magnets in anti-Helmholtz configuration (same poles facing each other). Positive difference between magnetic susceptibilities of radical solution (χ_medium) and gels (χ_object) leads to levitational assembly of gels.