Theoretical Description of Hydrogel Swelling: A Review

During the past decades, hydrogels have been introduced suitable as novelmaterials for a variety of applications such as biomedical engineering, sanitaryproducts, agriculture, bioseparation, enhanced oil recovery, etc. They havebeen successfully used as superabsorbent materials and in drug delivery, cellencapsulation and tissue repair due to their high water content and consequentbiocompatibility. Considering the fact that water retention in the hydrogels provides asuitable drug diffusion pathway; many hydrogel-based networks have been designedand fabricated as intelligent carriers of drugs. The rate and degree of hydrogel swellingare the most important parameters which control the release patterns of solvents anddrugs from these polymeric networks. Therefore, the precise account of hydrogelbehaviour as well as mathematical description of equilibrium swelling, dimensionalchanges due to solvent uptake, desorption and drug release profiles were the mainobjectives in many investigations. The objective of this manuscript is to give a briefreview on existing mathematical models and theories in the field of hydrogel swellingas well as the description of the drug release mechanism from swelling-controllednetworks. The most important properties of hydrogels relevant to their swellingbehaviour as well as kinetics and thermodynamic of swelling are also presented.