Hydrogels in Controlled Drug Delivery Systems

Hydrogels are a unique class of macromolecular networks that can hold a large fraction of an aqueous solvent within their structures. They are particularly suitable for biomedical applications, including controlled drug delivery, because of their ability to simulate biological tissues. Many hydrogel-based networks have been designed and fabricated to meet the needs of pharmaceutical and medical fields. The objective of this paper is to give a brief review on the fundamentals and recent advances in the design of hydrogel-based drug delivery systems (DDS) as well as the description of the release mechanism of bioactive molecules from these hydrogels. The structure and classification of hydrogels, swelling behaviour of hydrogels, different mechanisms of solvent diffusion into and drug release from hydrogels and mathematical description of these phenomena are elucidated. The most important properties of hydrogels relevant to their biomedical applications are also identified, especially for use of hydrogels as drug delivery systems. Kinetics of drug release from hydrogels and the relevant mathematical modelling are also reviewed in this manuscript.