Table 2.

Common photoinitiators for gelatin and its derivatives in light-based (bio)printing.

Photoinitiator	Chemical Structure	Activation Wavelength	Biocompatibility	Notes
Irgacure 2959	2-hydroxy-1-(4-(2-hydroxyethoxy)phenyl)-2-methylpropan-1-one	350-380 nm	Biocompatible (<0.3 wt%), toxic (>0.9 wt%)	Efficient in UV region; low efficiency in visible light spectrum
LAP	Lithium phenyl(2,4,6-trimethylbenzoyl)phosphinate	360-410 nm	Biocompatible (<0.5 wt%), toxic (>0.7 wt%)	High efficiency in visible light spectrum
Eosin Y	2’,4’,5’,7’-tetrabromo-3’,6’-dihydroxy-3H-spiro[isobenzofuran-1,9’-xanthen]-3-one	520-560 nm	Biocompatible (<0.05 wt%), toxic (>0.1 wt%)	Effective under visible light
Ru/SPS	Tris-bipyridyl-ruthenium (II) hexahydrate/Sodium persulfate	400-450 nm	Biocompatible (<1 wt%)	Effective under visible light; able to crosslink gelatin directly
VA-086	2,2’-(diazene-1,2-diyl)bis(N-(2-hydroxyethyl)-2-methylpropanamide)	345-380 nm	Biocompatible (<1.5 wt%)
Rose Bengal	Sodium 4,5,6,7-tetrachloro-2’,4’,5’,7’-tetraiodo-3-oxo-3H-spiro[isobenzofuran-1,9’-xanthene]-3’,6’-bis(olate)	520-560 nm	Biocompatible (<0.1 wt%)	Effective under visible light
Camphorquinone	1,7,7-trimethylbicyclo [2.2.1]heptane-2,6-dione	360-510 nm	Biocompatible (<1 wt%)	Low efficiency when used alone; high efficiency with tertiary amine as co-initiator
Riboflavin	7,8-dimethyl-10-((2S,3S,4R)-2,3,4,5-tetrahydroxypentyl)benzo[g]pteridine-2,4(3H,10H)-dione	300-670 nm	Biocompatible (<3 wt%)	Low efficiency