Abstract

Polymer coacervation is a long established and widely used method for the microencapsulation of solid or liquid drug compounds including biological macromolecules like DNA and proteins. The process has also been used to encapsulate live cells for immunoisolation and drug delivery (1). Coacervation may be defined as the phenomenon in which a colloidal dispersion is separated into two liquid phases, a colloid rich phase (the coacervate) and a colloid poor phase (2). The term is to be distinguished from precipitation, which is the result of destabilization in a colloidal system, and is observed in the form of coagulation or flocculation. The term coacervate is derived from the Latin word acervus meaning a heap or pile (3). It was introduced by Bungenberg de Jong and Kruyt in 1929 to describe a process, in which aqueous colloidal solutions separate into two liquid phases on alteration of the thermodynamic conditions of state (4). Coacervation may be subdivided into simple or complex coacervation based on the mechanism of phase separation. In simple coacer vation, the phase separation into two liquid phases may be induced by electrolytes, by addition of a miscible non-solvent, or by a change in temperature. The kinetics of simple phase separation has been discussed through statistical thermodynamic considerations by Gupta and Bohidar (5). Conversely, complex coacervation is driven by the attractive forces between oppositely charged polymers. The thermodynamics underlying complex coacervation has recently been reviewed by Veis (2).