ABSTRACT
The range of techniques for the preparation of microspheres offers a variety of opportunities to control aspects of drug administration. Simple coacervation is induced by a change in conditions, which results in dehydration of the macromolecules. The emulsion consists of polar droplets dispersed in a non-polar medium. The wettability of solids by different liquids is usually assessed by contact-angle measurement. When wetting of the core material is poor, it is difficult or impossible to form microcapsules. The problems associated with directing microspheres to specific areas in the body following parenteral administration are discussed in the article Colloids and Colloid Drug Delivery in this encyclopedia. Drug release from polymeric systems with a variety of geometries has been described. Zero-order release kinetics may be more easily achieved with slab or rod geometries than spheres. Diffusion-mediated release has been studied extensively and described mathematically.
