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.