Extended Data Fig. 3: Thickness-dependent difference of precipitation structures and damping performance.
a-c, Optical images of the precipitation patterns formed in hydrogels with different thicknesses, (a) 2 mm, (b) 4 mm, (c) 1 mm. The images on the right side of figure (b) show the cross-sectional morphology of the 4 mm hydrogel, where the precipitation bands do not fully penetrate through (Scale bars in surface morphologies, 5 mm; Scale bars in cross section, 2 mm). The precipitation patterns show dependence on thickness, there was well-defined periodic bands in the 2 mm hydrogel. And for the thicker hydrogel (4 mm), the bands appear only in the upper region because the downward diffusion of Cu2+ has a limited effective depth, and only the near-surface zone reaches the supersaturated concentration. In contrast, the 1 mm hydrogel generates discrete precipitation spots rather than continuous rings. This occurs because the very thin geometry amplifies local ion-concentration fluctuations, destabilizing the reaction front and causing it to fragment into isolated nucleation domains. Experiments were independently repeated at least three times with similar results. d-f, Evaluation of mechanical damping performance for metahydrogels with different matrix thickness and precipitation structures. For the 4 mm sample, the amplitude of the applied mechanical noise was modulated to assess the stability of its damping performance. g-i, Magnitude spectra calculated from the amplitude response of each sample relative to the reference signal.
