Synthesis and characterization of a hydrophobic association hydrogel for drug delivery

•A hydrophobic association hydrogel in an aqueous surfactant solution was prepared.•Water absorption of hydrogel increased with addition of a hydrophobic molecule.•Hydrophobic molecule gives a pH-dependent and retardant effect for caffeine release.•Caffeine release is controlled by swelling, macromolecular relaxation, and erosion.•Hydrogel is biocompatible with uses in delivery of poorly water-soluble drug. This work reports the synthesis, characterization, and evaluation of a hydrophobic association hydrogel containing vinyl alginate (SA), acrylamide, and the hydrophobic molecule N,N'-(disulfanediylbis(4,1-phenylene))diacrylamide (SPDAAm) for release of drug very slightly water-soluble in water. The SPDAAm molecule was synthetized with acrylic acid and 4-Aminophenyl disulfide and further characterized by H1 NMR spectroscopy. The hydrogel was prepared with a crosslinking chemistry using vinyl SA and acrylamide in an aqueous surfactant solution at a concentration less than the (critical micellar concentration) CMC. The introduction of SPDAAm in the hydrogel increases the swelling degree owing to hydrophobic association. Furthermore, SPDAAm gives a pH-dependent and retardant effect for caffeine (CFN) release. At a pH of 7.4, the CFN release mechanism is controlled by swelling, macromolecular relaxation of the polymer, and erosion of the hydrogel. The hydrogel with SPDAAm shows acceptable biocompatibility and has potential applications as a biomaterial in controlled release of poorly water-soluble molecules, like CFN.