REVIEW ON: RECENT ADVANCES IN THE STATE OF THE ART OF IN SITU FORMING INJECTABLE HYDROGEL SYSTEMS FOR THERAPEUTIC APPLICATIONS

In situ injectable gelling systems have been extensively investigated with the aim of being applied for minimally invasive drug delivery or injectable tissue engineering. This article explores the injectable in-situ gelling system for prolonged release parenteral drug delivery system and their strategies of preparation. Here, we describe in situ-forming injectable hydrogel systems, prepared usinga variety of chemical cross linkers or physical interactions, for application in drug delivery. There are many newer approaches for in situ injectable hydrogels that can be delivered in minimally invasive techniques such as injection, ocular or nasal administration while protecting drugs or cells from the hostile environment. Recently, the Michael addition reaction between thiol and vinyl groups, the click reaction between bis (yne) molecules and multi arm azides, and the Schiff base reaction have been investigated for generation of injectable hydrogels, due to the high selectivity and biocompatibility of these reactions. Non-covalent physical interactions have also been proposed as cross linking mechanisms for in situ forming injectable hydrogels. Hydrophobic interactions, ionic interactions, stereo-complex formation, complementary pair formation, and host-guest interactions drive the formation of 3D polymeric networks. In particular, supramolecular hydrogels have been developed using the host-guest chemistry of cyclodextrin (CD), which allows highly selective, simple, and biocompatible cross linking. Finally, we review the current state of the art of injectable hydrogel systems for application in drug delivery, cell therapy and tissue regeneration.