Toxicological Evaluation of Leachate-Preventing Hydrogel Photoinitiators

Current photoinitiators like (diphenylphosphoryl)(mesityl)methanone (TPO) are being regulatory phased out due to issues related to solubility, cytotoxicity, and leaching. Diazirines, a class of three-membered-ring photoinitiators, have been identified to address limitations of solubility, leaching, and toxicity effects as compared to TPO. Herein, two water-soluble diazirines are exposed to human keratinocyte (Ker-CT) cells for cytotoxicity evaluation. Exposure conditions are limited to initiator concentrations of 0.17-17 mM before (0 J) and after (10 J) UVA irradiation. Diazirine benchmarked to TPO maintained >90% cell viability at concentrations up to 17 mM, compared to a 20% reduction with TPO at 0.17 mM post-UVA. (4-(3-(trifluoromethyl)-3H-diazirin-3-yl)phenyl)methanol and 4-(3-(trifluoromethyl)-3H-diazirin-3-yl)benzoic acid (DzOH and DzCOOH) did not elevate mitochondrial superoxide above baseline levels. Elevated intracellular ROS levels correlated to diazirine dose, which could be due to controlled oxidative signaling. DzOH exhibited potential mitochondrial superoxide scavenging behavior under stimulated conditions. Diazirine-derived diazoalkanes spontaneously react with acrylamide monomers to form stable, non-toxic pyrazoline structures. Thus, the benign side product of UVA exposure mitigates the cytotoxicity associated with residual acrylamide. Incorporation of these diazirines into poly(ethylene glycol) diacrylate (PEGDA) - 575 hydrogels resulted in biocompatible materials with tunable water content (0-80 wt %) and negligible toxic leachates. Furthermore, cytotoxicity studies revealed cell type-dependent responses, with HeLa cells showing greater sensitivity than keratinocytes, suggesting potential for selective biological interactions. Overall, this study highlights water-soluble diazirine photoinitiators with low cytotoxicity, reactive oxygen species-modulating properties, and intrinsic detoxification capability.