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. Author manuscript; available in PMC: 2022 Apr 1.
Published in final edited form as: Prog Polym Sci. 2021 Feb 16;115:101375. doi: 10.1016/j.progpolymsci.2021.101375

Fig. 4.

Fig. 4.

Three representative photo-crosslinking mechanisms for 3D printing with proteins. A. Acrylate free-radical photo-crosslinking. Photo-initiators, such as LAP and Irgacure 2959, produce free-radicals under UV or visible light. Protein molecules are modified with acrylate groups at primary amine and hydroxyl groups. Free radicals lead to chain polymerization between methacryloyl groups from one (intra-) or different (inter-) molecules. Chain propagation is not shown for clarity. B. 1,4-dithiothreitol (DTT) is activated by UV or photoinitiators and reacts with C-C bonds, i.e., “ene” groups, for crosslinking. R in red color represents the immobilized group in the previous step. C. ([Ru(II)(bpy)3]2+) /persulfate-based photo-oxidation. The unstable intermediate is fortified by removing a hydrogen atom.