Micrometer resolution 3D printing through highly scattering media using upconversion nanoparticles

Light-based 3D printing shows great potential in biomedical applications by providing high-resolution features. However, its high-resolution capability is severely hindered in 3D printing through biological tissues because of the optically turbid nature of the tissue. Here, we demonstrate a high-resolution additive manufacturing technique through scattering media using upconversion nanoparticles (UCNPs) and the wavefront shaping method. It uses near-infrared (NIR) light to photopolymerize through the scattering media via UCNPs, which act as a secondary source for UV light as well as a beacon for wavefront shaping. By exploiting the optical nonlinearity of the upconverted fluorescence and the memory effect correlations, high-resolution printing is experimentally demonstrated through strongly scattering layers and biological tissues even when the signal is not localized. This technique provides a proof of concept of 3D printing through turbid media with potential applications for in vivo 3D bioprinting.