Design, Synthesis, and Application of a Water‐soluble Photocage for Aqueous Cyclopentadiene‐based Diels–Alder Photoclick Chemistry in Hydrogels

Spatiotemporally functionalized hydrogels have exciting applications in tissue engineering, but routes to pattern these materials typically rely upon 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 photocage for radical-free cyclopentadiene-based Diels–Alder click chemistry. We show that this scalable CPD–NBD derivative can be readily incorporated into hydrogel formulations and commercial 3D printing resins, providing hydrogels that can be patterned with dienophile-bearing species upon 365 nm uncaging of cyclopentadiene. The utility of this aqueous photoclick is demonstrated by the localized conjugation of maleimide dienophiles in both 2D hydrogel films and structurally complex 3D printed parts. Additionally, we demonstrate that the patterning of a maleimide functionalized adhesive peptide directs cellular adhesion to pre-programmed locations within hydrogels, highlighting the promise of this water-soluble photocaged cyclopentadiene as an inexpensive, versatile, and radical-free photoclick strategy to pattern molecules of interest into biocompatible hydrogel systems.