Influence of the ionic character of a drug on its release rate from hydrogels based on 2-hydroxyethylmethacrylate and acrylamide synthesized by photopolymerization

Abstract

The influence of the ionic character of a specific drug on its release rate from a hydrogel based on 2-hydrox- yethylmethacrylate (HEMA) and acrylamide (AAm) is analyzed. The hydrogel was synthesized by photopolymerization employing visible light, safranine O (Saf), as sensitizer, and a silsesquioxane functionalized with amine and methacrylate groups (SFMA), as co-initiator and crosslinker. Safranine O (Saf) was employed as a model of a cationic drug and the anionic form of resorufin (Rf) as a model of an anionic drug. Saf exhibited a larger affinity with functional groups of the hydrogel than that of Rf. This produced a lower loading and a faster release rate of Rf with respect to Saf. Besides, the release rate of Rf followed a Fickian behavior, while that of Saf exhibited a non-Fickian behavior. By hydrolyzing the hydrogel at pH = 13, amide groups supplied by AAm were irreversibly converted into carboxylic acid groups. Higher load- ings and slower release rates of Saf from the hydrolyzed hydrogels were observed, making them particularly suitable for the slow drug-delivery of cationic drugs.