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This work presents a general strategy for integrating photoresponsive molecules into liquid crystal elastomers (LCEs) using Diels–Alder chemistry. The method introduces various photochromes, offering a scalable route for multifunctional LCEs. 

Strategies that mimic the spatial complexity of natural tissues can provide cellular scaffolds to probe fundamental questions in cell biology and offer new materials for regenerative medicine. Here, we demonstrate a light‐guided patterning platform that uses natural ECM‐proteins as a substrate to program cellular behaviors. We utilize a photocaged diene which undergoes Diels–Alder based click chemistry upon uncaging with 365 nm light. By interfacing with commercially available maleimide dienophiles, we achieve patterning of common ECM proteins (collagen, fibronectin Matrigel, laminin) with readily purchased functional small molecules and growth factors. Finally, we highlight the use of this platform to spatially control ERK activity and migration in mammalian cells, demonstrating programmable cell behavior through patterned chemical modification of natural ECM. 

Abstract Light‐controlled chemical reactions have driven major advances in photo‐patterning and 3D printing, particularly for applications requiring spatially and temporally resolved control over soft material assembly. Synthetic hydrogels, which mimic the extracellular matrix, are widely used in 3D cell culture, drug delivery, and soft device platforms. While radical‐mediated photo‐crosslinking dominates digital light processing (DLP) bioprinting, the high reactivity of free radicals can compromise cell/biomolecule stability and functional group integrity. This issue has led to a shift toward radical‐free, light‐controlled crosslinking. In this study, a novel approach is presented for the first demonstration of radical‐free aqueous photo‐resins for DLP printing, utilizing photo‐caged cyclopentadiene (Cp) moieties and maleimide click partners. Upon 365 nm light exposure, uncaged Cp reacts rapidly with maleimide groups via a Diels–Alder cycloaddition, enabling fast gelation and high‐fidelity DLP printing. The two‐component resin system offers tunable mechanical properties and yields printed features with submillimeter fidelity. Critically, the resulting materials retain unreacted functional handles, enabling spatially resolved post‐functionalization with small molecules in the complete absence of radicals. This platform not only provides a robust and orthogonal alternative to traditional photo‐resins, but also opens new avenues for biofabrication, adaptive soft materials, and 4D‐printed systems where chemical precision and compatibility are paramount. 

An important but often overlooked feature of Diels–Alder (DA) cycloadditions is the ability for DA adducts to undergo mechanically induced cycloreversion when placed under force. Herein, we demonstrate that the commonly employed DA cycloaddition between furan and maleimide to crosslink hydrogels results in slow gelation kinetics and “mechanolabile” crosslinks that relate to reduced material strength. Through rational computational design, “mechanoresistant” DA adducts were identified by constrained geometries simulate external force models and employed to enhance failure strength of crosslinked hydrogels. Additionally, utilization of a cyclopentadiene derivative, spiro[2.4]hepta-4,6-diene, provided mechanoresistant DA adducts and rapid gelation in minutes at room temperature. This study illustrates that strategic molecular-level design of DA crosslinks can provide biocompatible materials with improved processing, mechanical durability, lifetime, and utility.