Figure 44 Synthesis of GelMA macromolecular monomers (A), cell
encapsulation (B), process of photopolymerization (C) and cell-laden
hydrogel materials (D).[157]
In view of these advantages including high efficiency, safety,
environmentally friendly and energy saving for visible light source,
Shao et al.[158] investigated the
photopolymerization kinetics of the PIS which is composed of
camphorquinone (CQ) and diphenyl iodonium hexafluorophosphate (DPI) that
have been widely used as a blue light PIS. Then a hydrogel was
synthesized by N, N-dimethylacrylamide (DMAA) and sodium acrylate (SA)
according to the kinetic results. The CQ/DPI system resulted in fast
polymerization and high double bond conversion (approximately 90 %)
when maximum polymerization rate was approximately 6.53 ×
10–5 s–1 with light intensity of
32.3 mW/cm2, 0.5 wt % CQ, and mass ratio of monomers
was 4 (DMAA):6 (SA). The hydrogel synthesized by poly (DMAA/SA) under
irradiation blue light displayed excellent water absorbability (about
750 g/g), robust mechanical properties (about 2500% strain and 0.6 MPa
stress) and fine dimensional stability. The kinetic mechanisms proposed
in this research can provide some reference for the synthesis of
hydrogels in biomedical field.
Naphthalimide derivatives have been widely employed as PI in the field
of visible light photopolymerization due to their excellent light
absorption properties in visible light region. Lalevée et
al.[39, 159] synthesized a series of naphthalimide
derivatives PIs that can be matched with LED sources with emission
wavelengths of 385 nm, 405 nm, 455 nm and 470 nm, chemical structures of
them are shown in Figure 45. The naphthalimide derivatives/additives
systems can effectively initiate cationic radical polymerization, among
them, NDP2 and 2,6-di-O-Me-β-cyclodextrin (DM-β-CD) can form
supramolecular complex NPD2-CD together, which exhibited excellent
solubility in water and good capacity of initiating polymerization of
hydroxyethyl acrylate (HEA) to obtain hydrogel at exposure to 405 nm LED
source, as shown in Figure 46.
Figure 45 Chemical structures of naphthalimide derivatives.