ABSTRACT
MICROENCAPSULATION is defined as enclosing a solid, liquid, or gas insidea polymeric coating. Microparticles for pharmaceutical applications are usually either solid or liquid core materials composed of either a drug or protein with a polymer. They are considered to be of two types: microcapsules, where the encapsulated drug or protein core is centrally located as a reservoir completely surrounded by a distinct capsule wall (membrane-walled); and micromatrices, often called microspheres, where the encapsulated drug or protein is a separate or homogenous dispersion throughout the microsphere matrix (Figure 14.1) (Burgess and Hickey, 1994; Kissel and Koneberg, 1996). Microparticles may have different structures depending on the application and encapsulation process. They are generally spherical particles with a size range of approximately 1 m to 2 mm; however, smaller sizes, such as nanoparticles, can be formed ranging from 10 to 1000 nm (Donbrow, 1992; Burgess and Singh, 1993; Burgess and Hickey, 1994).
