Figure 2.

4D shape-morphing behaviors of hydrogel bars in different incubation solutions or fabricated with different parameters. (a) Hydrogel bending angle kinetics in diH₂O, PBS (pH 7.4), and GM at room temperature. (b) Photomicrographs of deformed hydrogel bars in diH₂O, PBS (pH 7.4), and GM after swelling for 2 h. Effects of (c) infill density, (d) printing speed, (e) needle gauge, (f) UV irradiation time, (g) hydrogel bar width, and (h) hydrogel bar length on the bending angles of hydrogel bars cultured in PBS (pH 7.4) for 2 h at room temperature. UV absorber: 0.02% 4’-hydroxy-3’-methylacetophenone (HMAP), 0.005% methacryloxyethyl thiocarbamoyl rhodamine B (RhB) was incorporated to impart the hydrogel with red color for better clarity. Data are presented as mean ± SD, N = 3.