Photoinitiator-free visible-light bioprinting: minimising radical-induced oxidative stress and DNA damage in gelatin hydrogels

Light-mediated crosslinking of polymers is widely employed in the preparation of hydrogels for biofabrication and tissue engineering, since photo-crosslinking enables the spatiotemporal control over the gelation processes. Nevertheless, a critical bottleneck persists: most photo-crosslinking reactions rely on the use of photo-initiator, and ultraviolet or short-visible-wavelength light activation, which suffers from potential photodamage and poor penetration. Here we present a photoinitiator-free hydrogel system based on gelatin functionalized with acrylamidylpyrene groups (Gel-Pyr) able to undergo crosslinking via visible-light-induced [2+2] cycloaddition. Gel-Pyr solution exhibits rapid gelation kinetics, tuneable mechanical properties, facile temporal control over photocrosslinking, and long-term structural stability (>30 days) in cell culture conditions. Rheological analyses reveal pronounced shear-thinning behaviour at room temperature, enabling extrusion-based 3D bioprinting of multilayered constructs with high structural fidelity. Fine strand resolution (<400 {micro}m) is achieved in bioprinted crosshatch structures, enabling sufficient nutrient diffusion for cell support. Compared with gelatin methacryloyl (GelMA), Gel-Pyr significantly reduces photocrosslinking-induced oxidative stress and apoptosis in encapsulated bone-marrow mesenchymal stem cells (BM-MSCs), supporting >80% viability over 7 days. By eliminating UV exposure and lowering free radical generation, this visible-light-responsive hydrogel platform offers a facile and cytoprotective alternative to other hydrogel systems. Table of ContentA visible light-crosslinkable, initiator-free gelatin-based hydrogel (Gel-Pyr) is developed using acrylamidylpyrene functionalization. This system enables rapid crosslinking under cytocompatible reaction conditions and offers excellent printability, tuneable mechanics, and long-term stability. Gel-Pyr supports high cell viability, reduced oxidative stress and precision bioprinting, positioning it as a promising platform for tissue engineering and in vitro biofabrication. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=178 SRC="FIGDIR/small/691472v3_ufig1.gif" ALT="Figure 1"> View larger version (54K): org.highwire.dtl.DTLVardef@1f55f88org.highwire.dtl.DTLVardef@5308e2org.highwire.dtl.DTLVardef@16c538dorg.highwire.dtl.DTLVardef@e156ea_HPS_FORMAT_FIGEXP M_FIG C_FIG