Influence of photo-initiator concentration on the viability of cells encapsulated in photo-crosslinked microgels fabricated by microfluidics

Photo-initiators have long been used as a simple and effective photo-polymerization tool for biomedical applications such as cell-embedded scaffolds. Nevertheless, the influence of photo-initiators on cytotoxicity has not yet been comprehensively studied. Thus, we investigated the viability of cells encapsulated in gelatin methacrylate (GelMa) microgels in the presence of different concentrations of photo-initiator. GelMa microdroplets (5wt%)containing different concentrations of photo-initiator (0.2, 0.5, 0.7, and 1.0 wt%) were generated using a flow-focusing microfluidic device. Cells grown in GelMa microgels containing 0.2 wt% photo-initiator had high viability, suggesting that the photoinitiator was not cytotoxic at this concentration. However, at photo-initiator concentrations greater than 0.5 wt%, cell viability began to decrease; moreover, at 1.0 wt%, almost no live cells were observed. The decreased cell viability associated with increased concentrations of photo-initiator is probably a result of residues and byproducts from reactions with photo-initiators. This detailed study of the relationship between cell viability and photo-initiator concentration can inform the development of future photocrosslinking strategies used in cell-laden hydrogel applications.