Fig. 2. Concept of the fabrication strategy based on magnetically driven transformation.

(A) Schematic illustration showing (i) deposition of materials into a flat hydrogel precursor, (ii) submerged transformation into a 3D morphology upon magnet application. F_m represents the magnetic force applied on the hydrogel, F_b represents the buoyancy force, G represents the gravitational force of the scaffold material, and G_a represents the gravitational force of the additionally implemented gravity ink. (B) 4D printing of 3D branching vascular geometries using the magnetically driven transformation strategy. The geometry designs were generated in AutoCAD (i), printed into flat hydrogel precursors (ii), and then transformed into 3D branching geometries using a magnet (iii). Scale bars, 1 cm.