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Abstract 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, the authors demonstrate a light‐guided patterning platform that uses natural engineered extracellular matrix (ECM) proteins as a substrate to program cellular behaviors. A photocaged diene which undergoes Diels–Alder‐based click chemistry upon uncaging with 365 nm light is utilized. By interfacing with commercially available maleimide dienophiles, patterning of common ECM proteins (collagen, fibronectin Matrigel, laminin) with readily purchased functional small molecules and growth factors is achieved. Finally, the use of this platform to spatially control ERK activity and migration in mammalian cells is highlighted, demonstrating programmable cell behavior through patterned chemical modification of natural ECM. 

Abstract Spatiotemporally functionalized hydrogels have exciting applications in tissue engineering, but their preparation often relies on radical‐based strategies that can be deleterious in biological settings. Herein, the computationally guided design, synthesis, and application of a water‐soluble cyclopentadienone‐norbornadiene (CPD‐NBD) adduct is disclosed as a diene photocage for radical‐free Diels‐Alder photopatterning. We show that this scalable CPD‐NBD derivative is readily incorporated into hydrogel formulations, providing gels that can be patterned with dienophiles upon 365 nm uncaging of cyclopentadiene. Patterning is first visualized through conjugation of cyanine dyes, then biological utility is highlighted by patterning peptides to direct cellular adhesion. Finally, the ease of use and versatility of this CPD‐NBD derivative is demonstrated by direct incorporation into a commercial 3D printing resin to enable the photopatterning of structurally complex, printed hydrogels. 

Catalyst-free and reversible step-growth Diels–Alder (DA) polymerization has found a wide range of applications in polymer synthesis and is a promising method to fabricate recyclable thermoplastics. The effectiveness of polymerization and de-polymerization relies on the chemical building blocks, often utilizing furan as the diene and maleimide as the dienophile. Compared to the traditional diene–dienophile or two-component approaches that requires perfect stoichiometry, cyclopentadi-ene (Cp) can serve a dual role via self-dimerization. This internally balanced platform offers a route to access high-molecular-weight polymers and a dynamic handle for polymer recycling, which remains unexplored. Herein, through the reactivity in-vestigation of different telechelic Cp derivatives, the uncontrolled cross-linking of Cp was addressed, revealing the first suc-cessful DA homopolymerization. To demonstrate the generality of our methodology, we synthesized and characterized six Cp homopolymers with backbones derived from common thermoplastics, such as polydimethylsiloxane, hydrogenated poly-butadiene, and ethylene phthalate. Among these materials, the hydrogenated polybutadiene-Cp analog can be thermally de-polymerized (Mn = 68 to 23 kDa) and re-polymerized to the parent polymer (Mn = 68 kDa) under solvent- and catalyst-free conditions. This process was repeated over three cycles without intermediate purification, confirming the efficient thermo-selective recyclability. The varied degradable properties of other four Cp-incorporated thermoplastics were also examined. Overall, this work provides a general methodology to access a new class of reversible homopolymers, potentially expanding the designs and construction of sustainable thermoplastics.