Synthesis of hydrogels by visible-light photopolymerization: Photochemical characterization of the initiator system and model drug-release studies at neutral pH

GÓMEZ, M.L; R. J. J. WILLIAMS; H. A. MONTEJANO; C. M. PREVITALI

Heredia

Simposio; XII Simposio Latinoamericano de Polímeros SLAP; 2010

SLAP

A drug delivery system based on acrylamide and 2-hydroxyethylmethacrylate hydrogels synthesized by photopolymerization is reported. The photoinitiator system was characterized. It is composed by safranine, as sensitizer for visible light with a silsesquioxane functionalized as co-initiator and crosslinker. Under these conditions a monomer conversion near 80% was reached (1). The photoinitiation was based on the deactivation of both singlet and triplet excited states of safranine by the silsesquioxane through an electron transfer reaction. The quenching of the singlet state of Saf by SFMA in aqueous solution was determined by time-resolved fluorescence. The singlet quenching rate constant, obtained by Stern-Volmer analysis, was 1.60e9 M-1 s-1. The triplet state quenching of the dye by SFMA was investigated by Laser Flash Photolysis by monitoring the decay at 805 nm. The resulting bimolecular quenching rate constant was 2.50e7 M-1 s-1; values lying in the range of quenching rate constants previously reported for the quenching of Saf by aliphatic amines (2). The guest-host interactions were studied employing safranine-O (Saf), acridine orange (AO) and resorufine (Rf) as cationic, neutral and anionic dyes, respectively, as model drugs for the release studies at neutral pH. The cumulative release (CR) was then calculated and plotted as a function of time (3). As can be shown from Fig. 2, hydrogels showed higher release for anionic or neutral dyes. Converting the amide groups supplied by acrylamide, into carboxylic acid groups, by the hydrolysis of the hydrogels at pH = 13, higher loadings and slower release rates of the cationic drug from the hydrolyzed hydrogels were observed. Finally, preliminary results for the release of aspirin, incorporated during the photopolymerization of hydrogels are shown in Figure 3. A release near 30% was achieved in 8 hours.We can conclude that the studied hydrogels based on HEMA and AAm are suitable as drug delivery systems for control release. Preliminary results show that is possible performed the synthesis of hydrogels in the presence of a drug like aspirin employing visible light polymerization.