Fig. 3.

Photosynthesis-assisted strengthening with patterned light. (A) Schematic of an experimental setup for the localized strengthening through a patterned light with an S shape. (B) Samples at the as-printed state and after 4-h illumination with an S-shaped light and 4-h darkness. (C) Young’s modulus distribution of the patterned sample measured with indentation tests. (D) Average stiffness of the unstrengthened and strengthened regions. (E) Crack detouring in a plate sample with a strengthened circle. (F) Straight crack in a plate sample without a strengthened circle. (G) Load-displacement curves of samples with and without the strengthened circle. (Inset) The loading setup. (H) Crack paths of samples with and without wavy strengthened regions. (I) Schematic to illustrate a 3D-printed lattice structure processed by a graded light (Left to Right: 69.3–0 ${\text{W/m}}^2$). (J) Samples of functionally graded, fully soft, and fully stiffened lattices. (K) Effective Young’s modulus distribution of three samples measured with indentation tests. (L) Compressive force-displacement curves of three samples with a loading rate of 10 mm/s. The loading is along the longitudinal gradient direction (x direction). (M) The absorbed energy of the three samples. The error bars in D and M represent SDs of 3–5 samples. Note that the inhomogeneous green color in E, F, and H is possibly due to some clusters of broken chloroplasts produced during the extraction experiments, which do not influence the result quality.