Forming three-dimensional micro-objects using two-dimensional gradient printing

•A 2D-to-3D shape-transformation approach was developed through building internal stress in a commercial polymer resin, requiring no external stimuli or special materials.•Multi-mode 2D-to-3D shape transformations including bending, rolling, coiling, waving, spiraling, and out-of-plane distortions were realized either individually or simultaneously.•Various 3D geometries including micro-coils, waves, caps, flowers, helices, and micro-origamis were formed with their transformation states being precisely controlled.•The intrinsic limitations of stepping and stitching in direct 3D printing were circumvented, achieving 3D objects with much smoother surfaces and improved integrity.