Evaluating Cross-Linking Efficiency and Cytocompatibility of Three Commonly Used Photoinitiators across Different Cell-Compatible Hydrogel Platforms

Biomedical hydrogels often use a photopolymerization strategy to cross-link the polymer network. There are only a few cyto-compatible photoinitiators (PIs) that are commonly used for cross-linking biomedical hydrogels, including Irgacure 2959, lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP), and Eosin Y. Herein, we tested these PIs to optimize the cross-linking efficiency while minimizing cell death. Testing was performed on three types of hydrogels, including a synthetic material (poly(ethylene glycol)-diacrylate, PEG-DA), a semisynthetic material, PEG-fibrinogen (PF), and a modified biological material, methacrylated fibrinogen (FibMA). The results showed that PI concentration and illumination intensity had a significant impact on cross-linking efficiency, as measured by the shear storage modulus, with each material demonstrating different responses to the photopolymerization parameters. Optimal photo-cross-linking conditions were not the same for the modified protein hydrogels as compared to synthetic and semisynthetic materials. These findings may have consequential implications when applying photopolymerization to cross-link various types of cell-compatible hydrogels for biomedical applications.