Fig. 2. Mechanical characterization of the picospring material based on a cantilever method.
a, Schematic illustration of the characterization on a picospring array by an optical trap. The characterization structure has a cantilever picospring and two short bars at the free end, forming a holder for an action microbead pulled by the optical trap to stably deform the picospring. The load is applied parallel to the cross-section of the cantilever by the trapped microbead. When the microbead is moved at a negligible velocity to deform the cantilever picospring, the elastic force of the cantilever picospring approximately equals the trapping force provided by the optical trap. Rigid parts are coloured grey and flexible picosprings are coloured blue in the right panel. We use 25 mW to fabricate all nominally rigid parts. b, Cantilever picospring deformations under a certain load of 25.4 pN showing a negative correlation between the cantilever deflection and the fabrication laser power. Samples with or without MNPs represent the microstructures based on elastomeric materials with or without MNPs. c, Increasing Young’s modulus of the elastomeric material with respect to the fabrication laser power. n = 3 independent samples, mean ± s.d. Under small deformations, Young’s modulus E of the cantilever picospring is calculated by an approximate formula E = FL2/3Iθ (θ < 20°), where F, L and I represent the load force, the cantilever length and the moment of inertia of the cantilever, respectively. θ is defined as the deflection angle of the load position to the fixed end of the cantilever. d, Sequential deflection images of the cantilever picospring fabricated at 5.5 mW under increasing loads. Inset: finite element analysis results. Scale bar, 10 μm.