Interaction of microspheres with blood constituents. III. Macrophage phagocytosis of various types of polymeric drug carriers

Biodegradable polymers in the form of microparticulate drug carriers in the 1 to 5 μm size range have been found to interact with cultured monocytes-macrophages. Peritoneal exudate cells harvested from female mice were analyzed for their capacity to internalize particles of the synthetic polymers, poly(glycolic acid), a copolymer of polyglycolic and polylactic acids, a derivative of the natural polymer, hydroxyethyl starch, and 2 inert polystyrene microspheres. Uptake of all the microparticles appeared to occur rapidly once contact was made between the particle and the cell surface. The interaction with the macrophages was quantitatively assessed by determining the ratio of the area of phagocytized particles to the cytoplasmic area in the cell. Maximum loading in all cases occurred in 6-8 hours and biodegradation or digestion was evident within 24 hours with the hydroxyethyl starch microspheres and within 48 hours with the others. The results suggest that systemic or local targeting of drugs and proteins to macrophages with biodegradable polymers is a viable option worthy of additional development.