"Development of a 3D Printable Resin Cured via Diels-Alder Photoclick Chemistry"

Takashi Kaneko,^1,3 Sophia J. Bailey,^1,3 Ronnie V. Garcia,^1,3 Sijia Huang,⁴ Maxim Shusteff,⁴ Craig J. Hawker,^1,2,3 Javier Read de Alaniz^1,3

1: Department of Chemistry & Biochemistry, University of California, Santa Barbara
2: Materials Department, University of California, Santa Barbara
3: BioPACIFIC Materials Innovation Platform, University of California, Santa Barbara
4: Lawrence Livermore National Laboratory

3D Printing has enabled widespread applications in bioprinting and tissue engineering to mimic the complex structures of natural cells and tissues. However, conventional 3D printing strategies are based on radical photopolymerization reactions which can be damaging to biological systems. Radicals produced during initiation and propagation can decrease cell viability or modify proteins through unwanted side reactions. It is therefore highly desirable to develop alternative 3D printing strategies that are not based on radical chemistry, are highly selective and compatible with biological systems. Inspired by the high reactivity of cyclopentadiene (Cp) and its advantages in macromolecular click reactions, we have recently reported the development of photo-gated Cp derivatives that enable efficient bioconjugation and 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 3D printing that can undergo rapid gelation due to the Diels-Alder click reaction. Preliminary studies have demonstrated that on irradiation with light, these systems rapidly form hydrogel networks in an additive and radical-free step-growth gelation. The rheological properties of the resulting hydrogel networks were characterized under UV irradiation, demonstrating its photo-curability for 3D printing applications. Notably, the resin was air-tolerant owing to the absence of a radical-based polymerization mechanism. To showcase its printability, the resin was employed with the state-of-the-art DLP 3D printer to fabricate a 3D-structured hydrogel with high fidelity, demonstrating the potential of photo-gated click chemistry for biocompatible 3D printing.