Fig. 4: High-precision 3D printing colorful koi fish structures.

a Scheme of the preparation process of 3D koi fish structure with multi-structural colors. b Optical image of the multi-structural color koi fish continuously printed with four different PS latex particle diameters. The dashed curves represent the interface of two segments printed with different PS latex particle diameters. I–IV are the segments printed from the PS latex particle diameters of 192 nm, 214 nm, 230 nm, and 265 nm, respectively. The inset on the bottom left is the 3D model of koi fish. c–f Cross-sectional optical images of I (c), II (d), III (e), and IV (f) in (b), respectively. g–j SEM images of the head (g), gill (h), scale (i), and fin (j) of the 3D printed koi fish structure. k Surface SEM image of the interface between the segments I and II in (b), the two sides of the interface are printed from the PS latex particle diameters of 192 nm and 214 nm, respectively. l, m Cross-sectional Micro-CT images of the internal (l) and tail (m) of the 3D printed koi fish structure, indicating that the printed structure has excellent fidelity and high precision. n Reflectance spectra of the I–IV segments in (b). o Optical image of the 3D printed koi fishes with single or multi-structural colors. Waterweed structures are plastic decorations.