Grafted thermo-responsive gelatin microspheres as delivery systems in triggered drug release

In this paper, a novel class of microspheric hydrogels was synthesized by grafting of N-isopropyacrylamide (NIPAAm) with gelatin. The possibility of inserting commercial gelatin in a crosslinked structurebearing thermo-sensitive moieties, by radical process, represents an interesting innovation that signifi-cantly improves the device performance, opening new applications in biomedical and pharmaceuticalfields. This synthetic approach allows a modification of the polymeric network composition, producinghydrogels with suitable physico-chemical properties and a transition temperature higher than NIPAAmhomopolymers. The incorporation of monomers into the network was confirmed by infrared spectroscopy, and the composition of the polymerization feed was found to strictly influence the network densityand the shape of hydrogels. Thermal analyses showed negative thermo-responsive behaviour withshrinking/swelling transition values in the temperature range 34.6–34.8 C, according to the amount ofthe hydrophilic portions in the network. In order to test the preformed materials as drug carriers, diclofenac sodium salt was loaded into the spherical microparticles. After the determination of the drug entrapment percent, drug release profiles in media at different temperature were analysed. By using semiempirical equations, the release mechanism was extensively studied and the diffusional contributionwas evaluated.