Digital light processing of photoresponsive and programmable hydrogels

Light-mediated manipulation of hydrogel physicochemical properties is attractive for numerous applications, yet the processing of such hydrogels via vat photopolymerization [e.g., digital light processing (DLP)] is challenging as photoresponsive chemistries may be consumed during printing. Here, we report a facile strategy to DLP print hydrogels that combines short light exposures to set the shape of a printed object and complementary dark polymerization to continue the reaction of macromers without disturbing photoresponsive groups. Postprinting, hydrogels are then programmed using single- or multiphoton light and photoinitiator-free reactions: tetrazole-alkene click reaction (for photofunctionalization), dithiolane ring-opening polymerization (for photostiffening), and o-nitrobenzyl cleavage (for photosoftening). We demonstrate the versatility of this approach through applications that include the patterning of ligands to direct cell-material interactions, four-dimensional shape morphing, and bottom-up construction of multiscale models, including microscale perfusable channels. This approach provides access to highly tunable 3D-printed photoresponsive hydrogels for a range of soft matter applications.