Fig. 3: 3D printing hierarchical structures with tunable segregation.

a Schematic of the working principle of DLP printing hierarchical structures with segregation. b Cross-sectional optical microscopy image and (c) SEM image of a sample photocured with 1% w/v TPO under the irradiance of 4.0 mW cm⁻². Scale bar, 20 μm in (b) and 5 μm in (c). d Vertical distribution of silica nanoparticles in a single printing layer with 0.5% w/v TPO and curing intensity ranging from 2.0, to 4.0, 11.6, 18.6, and 28.0 mW cm⁻². e A contour plot of segregation thickness as a function of irradiance and photoinitiator concentration. f A plot of segregation thickness versus \({c}_{{{\rm{PI}}}}^{-0.30}{I}^{-0.28}{\phi }^{0.96}\). The scattered points are experimental data and the line is based on a linear fitting with coefficient of determination of \({R}^{2}=\) 0.962. g Segregation thickness in different acrylic resins with 1% w/v TPO under the irradiance of 2.0 mW cm⁻². h Segregation thickness for samples with different nanoparticles. All the samples are made from photonic ink containing 15% v/v 128 nm silica nanoparticles. All data are presented as mean values ± standard errors of the mean (n = 3).