Fig. 1. Fabrication of picospring-based micromachines with programmable elasticity distributions.

a, Schematic illustration of the 3D nanofabrication based on TPL. The photoresist contains an elastomer (urethane acrylate oligomer, UAO), a hydrogel (poly(ethylene glycol) diacrylate, PEGDA) and embedded MNPs. MNPs comprise only 3% of the photoresist to avoid the laser scattering during lithography. The local elasticity is dependent on the spatially programmed fabrication laser power. The picosprings are responsive to piconewton-scale forces, such as those arising from microswimmers or from driving magnetic fields. Picosprings perform specific functions in customized soft micromachines with different configurations. b, 3D-reconstructed geometries of the fixed cantilever and coil picosprings based on stacked fluorescence images taken by confocal laser scanning microscopy showing the independence of fabrication geometry on MNP content. Inset: the cantilever width averaged at 440 nm. c, Mechanical simulation results showing the deformations of four types of picospring. The load forces are applied parallel to the cross-section of the springs. d, Fabricated picosprings (top) and their deformations (bottom) under magnetic loads. Scale bar, 10 μm.