Phagocytosis of Polymeric Microspheres

One of the important objectives in the current drug therapies is the selective delivery of drugs and diagnostic agents to a specific site or organ in the body, which would result in a reduction of unwanted side effects and adverse reactions. Drug delivery may be achieved with the use of a wide variety of drug carriers including macromolecules and colloidal systems, such as polymeric microspheres, liposomes, and emulsions. However, few investigations have been carried out on the interaction between polymeric microspheres and macrophages (Mø), which are the main cells of mononuclear phagocyte systems directly responsible for the clearance and disposition of the microspheres injected into the body. This article views the phagocytosis of polymeric microspheres by Mø, focusing the physicochemical characteristics of the microspheres such as their size, surface charge, and surface hydrophobicity. It is demonstrated that the variation of these characteristics leads to a remarkable alteration in the Mø phagocytosis of the microspheres, regardless of the properties constituting the microspheres. The findings will provide information useful for the fate and distribution of the microspheres injected into the body, and a guidance for the development of polymeric microspheres as carriers applicable for drug delivery systems.