Enhancement of visible light-induced gelation of photocurable gelatin by addition of polymeric amine

We evaluated the effect of an electron donor on photogelation of photocurable gelatin, which is gelatin partially derivatized with eosin (eosin–gelatin). As an electron donor, ascorbic acid, 2-(N,N-dimethylamino)ethyl methacrylate (DMAEMA), and three kinds of radical polymerized amines such as poly(N,N-dimethylacrylamide-co-2-(N,N-dimethylamino)ethyl methacrylate) (poly(DMAAm-co-DMAEMA)), poly(N,N-dimethylacrylamide-co-3-(N,N-dimethylamino)propyl acrylamide) (poly(DMAAm-co-DMAPAAm)), and poly(3-(N,N-dimethylamino)propyl acrylamide) (polyDMAPAAm) were examined. Upon photo irradiation at the wavelength ranging from 400 to 520 nm with low illumination intensity (7.7 × 103 lx), no gel was obtained from 20 wt.% of a viscous aqueous solution of the eosin–gelatin even by adding with ascorbic acid. Whereas in the presence of monomeric amine (DMAEMA, 3.0 wt.%), gel formation occurred by radical recombination between eosin groups incorporated into the gelatin. When the polymeric amines were added to the eosin–gelatin solution, gelation was markedly enhanced due to cross-linking of gelatins through polymeric amines in addition to direct bonding between gelatins. An increase in amine unit content in the polymeric amines resulted in increased gel yield and reduced swelling degree of water. In the presence of polyDMAPAAm, almost all gelatins were converted relatively rigid hydrogel. Application for a topical hemostatic glue was preliminary performed in rat injured model. A rat liver injured in laparotomy was coated with the aqueous eosin–gelatin solution containing polyDMAPAAm. Upon irradiation, the solution was immediately converted to a swollen gel, which was tightly adhered to the liver tissue and concomitantly hemostasis was completed with little tissue damage.