Polyelectrolyte Complexes: Introduction and Application-Part I

Polymeric materials carrying positive and/or negative charges at neutral pH are referred as "polyelectrolytes". Many kinds of materials are considered as polyelectrolytes because they bear ionic groups of positive or negative charges on their surfaces. The interaction between two or more opposite charged polyelectrolytes in solution forms a polyelectrolyte complex (PEC). Polymers used for PEC formation are classified on the basis of origin as natural and synthetic. The worldwide agreement among investigators is that the PEC formation is an entropy-driven phenomenon. The contributing force for the formation of PECs in aqueous solutions is the release of low molecular weight counter ions (which were previously associated with the charged groups on polymer chains) that result in an increase in entropy of the system. PECs have many advantages such as high biodegradability, excellent biocompatibility, non-toxicity, low cost, low energy requirement for their production. There are numerous parameters affecting PEC formation including charge density, molecular weight, and salt concentration, pH of the reaction medium, ionic strength and mixing ratio. This article presents the properties of PEC, mechanism of PEC formation, factors affecting the formation of PEC, different methods for PEC synthesis and application of PECs. PEC is an emerging system for drug delivery to target sites, sustained and thereby prolonging the therapeutic action. They are also used in gene, protein and vaccine delivery, tissue engineering and fabrication of membranes.