Alt text
Figure 2: Schematic illustrations and mechanical analyses of the programmed 3D deformations. (a) The scheme shows the differences of the Ca2+ ions diffusion and cross-linking density at different areas of the hydrogel sheet. (b) The cross-sectional field-emission-scanning electron microscopy (FE-SEM) images of the frozen dried hydrogel and the magnified images of the top surface and the bottom surface. (c) Increasing the pre-cross-linking time increases Young’s moduli at the three representative areas of the hydrogel sheet. (d) Young’s modulus decreases across the thickness from the top surface of the hydrogel sheet, which is 57.55±0.91 MPa for the top surface, 14.94±0.73 MPa for the valley, and 1.42±0.038 MPa for the ridge, respectively. (e) Young’s modulus mechanical maps for the top surface, valley (f), and ridge (g), respectively.