Table 2.

Summary of the main water-soluble initiators used in biomedical applications, their basic properties, and photo induced cleavage of photoinitiators.

Type of Initiator	Name of Initiator	Structure, Together with a Simplified Scheme of Photoinduced Cleavage of Photoinitiator	Maximum Absorbance / Source of Irradiation	Key Strengths	Key Drawbacks	Ref.
Type I	Irgacure 2959		276 nm/ 365 nm	High initiation rate, low cytotoxicity, and immune- genicity	Low initiation efficiency, need for UV light sources, low water solubility (<5 w.%)	[104]
Type I	TPO		267, 298, and 380 nm	Cleaves into highly reactive radicals, good thermal stability	Poor water solubility	[146]
Type I	LAP		375 nm/ (320-390 nm) 405 nm	Good water solubility, possibility of using UV and visible light sources	Low initiation efficiency, especially when exposed to light from the visible range	[138], [142]
Type I	BAPO-OLi		375 nm/ (320-420 nm)	Good water solubility ~54 g/l	Very low extinction coefficient in the range above 400 nm	[142,143,144]
Type I	VA-086		365 nm/ (365-385 nm)	Low toxicity, providing 90% cell survival, high initiation rate, good water solubility	Released nitrogen causes bubble formation	[97], [150,151,152]
Type II	Eosin-Y		528 nm/ (400-800 nm)	Good water solubility, low cytotoxicity, wide range of absorbance, possibility to use different light sources in visible range, possibility to use low light powers	A second ingredient is needed for high initiation efficiency – the co-initiator	[158], [159,243]
Type II	Camphor- quinone		444 nm/ (400 -500 nm)	Wide absorption range based on the visible range	Modification needed to increase solubility in water, strongly yellow after reaction	[105], [186]
Type II	Riboflavin		223, 267, 373 and 444 nm / (300-500 nm)	Excellent water solubility, wide absorption range, also in the visible area, non-toxic, beneficial to cells	Possibility of creating reactive oxygen species	[167], [177]
2PP	WSPI		source of irradiation: laser – 800 nm	very good water solubility, excellent optical sensitivity, and resolution, no toxicity	significant limitations of speed fabrication	[207] [221] [244]
2PP	BDEA					[224]
2PP	P2CK					[225]