The potential of 3D printing technologies, particularly in the biomedical field, is being significantly enhanced by innovations in hydrogel chemistry combined with digital light processing (DLP) strategies. DLP offers unique advantages, especially for producing complex structures like cell-laden tissues. However, traditional DLP techniques predominantly utilize radical photopolymerization of acrylate monomers, which can pose challenges for biological applications where the generation of radicals can adversely affect cell viability and alter proteins through unintended side reactions. To address these limitations, we have explored Diels–Alder (DA) cycloadditions due to their high selectivity and compatibility with biological systems. Diels–Alder (DA) cycloadditions are preeminent click reactions, unlike other common click chemistries that rely on toxic additives. Inspired by the high reactivity of cyclopentadiene (Cp)for DA click reactions,we have recently reported the development of photo-gated Cp derivatives that enable efficient bioconjugationand control of polymer click reactions without the need for radicals. Herein, we utilized this photo-gated Cp strategy for the development of novel photo-resins for DLP printing of hydrogel materials that are formed by rapid gelation via the DA click reaction between Cp and maleimide. As a result, the photo-resin rapidly formed hydrogel networks on irradiation with light, through an additive and radical-free step-growth gelation process. Photo-rheology studies on the gelation of the resin revealed that the resin has an efficient photo-curability. Additionally, we have shown that the resin is suitable for post-functionalization of the 3D-printed hydrogels, showcasing the potential of photo-gated click chemistry for accessing next-generation 3D-printed materials. This development paves the way for next-generation 3D-printed biomaterials that are not only effective for various applications but also safe for biological systems, ultimately enhancing the functionality and integration of printed tissues and devices in the biomedical landscape.

Angela Pitenis

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