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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), ando-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. 

Polyacrylamide tanglemers with photodegradable crosslinkers afford spatiotemporal control over the stability of entanglement-trapping crosslinks, influencing regional swelling and increased extensibilityviachain lengthening. 

Abstract Hydrogels are often synthesized through photoinitiated step‐, chain‐, and mixed‐mode polymerizations, generating diverse network topologies and resultant material properties that depend on the underlying network connectivity. While many photocrosslinking reactions are available, few afford controllable connectivity of the hydrogel network. Herein, a versatile photochemical strategy is introduced for tuning the structure of poly(ethylene glycol) (PEG) hydrogels using macromolecular monomers functionalized with maleimide and styrene moieties. Hydrogels are prepared along a gradient of topologies by varying the ratio of step‐growth (maleimide dimerization) to chain‐growth (maleimide‐styrene alternating copolymerization) network‐forming reactions. The initial PEG content and final network physical properties (e.g., modulus, swelling, diffusivity) are tailored in an independent manner, highlighting configurable gel mechanics and reactivity. These photochemical reactions allow high‐fidelity photopatterning and 3D printing and are compatible with 2D and 3D cell culture. Ultimately, this photopolymer chemistry allows facile control over network connectivity to achieve adjustable material properties for broad applications. 

Abstract Granular biomaterials have found widespread applications in tissue engineering, in part because of their inherent porosity, tunable properties, injectability, and 3D printability. However, the assembly of granular hydrogels typically relies on spherical microparticles and more complex particle geometries have been limited in scope, often requiring templating of individual microgels by microfluidics or in‐mold polymerization. Here, we use dithiolane‐functionalized synthetic macromolecules to fabricate photopolymerized microgels via batch emulsion, and then harness the dynamic disulfide crosslinks to rearrange the network. Through unconfined compression between parallel plates in the presence of photoinitiated radicals, we transform the isotropic microgels are transformed into disks. Characterizing this process, we find that the areas of the microgel surface in contact with the compressive plates are flattened while the curvature of the uncompressed microgel boundaries increases. When cultured with C2C12 myoblasts, cells localize to regions of higher curvature on the disk‐shaped microgel surfaces. This altered localization affects cell‐driven construction of large supraparticle scaffold assemblies, with spherical particles assembling without specific junction structure while disk microgels assemble preferentially on their curved surfaces. These results represent a unique spatiotemporal process for rapid reprocessing of microgels into anisotropic shapes, providing new opportunities to study shape‐driven mechanobiological cues during and after granular hydrogel assembly.