Among the many biomaterial platforms explored for pharmaceutical use, hydrogels occupy a singularly compelling position — they mimic the water-rich architecture of living tissue while offering a programmable scaffold for drug containment and release. This article examines the growing relevance of hydrogel technology in the design of controlled drug delivery systems (CDDS), tracing its intellectual lineage from early polymer chemistry to present-day stimuli-responsive applications. We systematically address how hydrogels are categorised by their composition, network topology, ionic identity, and cross-link chemistry, and how each of these variables shapes the eventual pharmacokinetic behaviour of the formulation. Special attention is given to injectable and in situ-gelling architectures — including shear-flow-responsive gels and thermoset peptide assemblies — as well as to the continuum from macroscopic implants to colloidal nanogel suspensions. The mathematical underpinnings of drug transport through these matrices are presented alongside illustrative clinical correlates. Delivery applications spanning parenteral, enteral, rectal, and cutaneous routes are surveyed, and a curated summary of authorised hydrogel products on the global market is provided. The review concludes with a forward-looking discussion of intelligent hydrogels, three-dimensional bioprinting, and translational bottlenecks that must be addressed before the next generation of hydrogel therapies reaches patients.
Chakraborty* et al. (Mon,) studied this question.