Enhanced Near-Infrared Light-Mediated Hydrogel Curing Using Photoinitiator Integrated Upconversion Particles as Nano Initiator for 3D Bioprinting.

In vivo three-dimensional (3D) bioprinting is a promising strategy that can enable personalized organ repair with minimal injury. The current in vivo 3D bioprinting based on upconversion nanoparticles (UCNPs) mediating near-infrared (NIR) light curing is still limited by the low hydrogel cross-linking efficiency. Herein, we introduced a bioink system that allows enhanced NIR light curing by utilizing thiol-ene cross-linkable polymers and photoinitiator-modified UCNPs@LAP nano initiator. The norbornene functionalized hyaluronic acid (NorHA) and thiolated gelatin (GelSH) were first synthesized to prepare the thiol-ene polymer solution. Compared to radical cross-linkable gelatin methacryloyl (GelMA), the NorHA/GelSH exhibited much higher reactivity under weak photoinitiating conditions. With the addition of surface-modified UCNPs@LAP nano initiator, the bioinks showed improved NIR curing performances, which is beneficial to reduce potential thermal damage. Furthermore, in vitro evaluation showed that the NIR light-cured 3D scaffolds preserved excellent bioactivity, suggesting that the hybrid bioink holds great promise to serve as a candidate for in vivo 3D bioprinting.