Acrylic microspheres in vivo IX: Blood elimination kinetics and organ distribution of microparticles with different surface characteristics.

The elimination of microparticles from blood after intravenous injection is dependent on the surface characteristics of the particles. The half-life in blood increases from 44 to 84 min after modification of surface-localized human serum albumin with polyethylene glycol. Irrespective of the surface properties, particles are localized in the reticuloendothelial system, mainly in the liver and spleen. In preimmunized mice, the distribution of particles is somewhat altered, i.e., the liver and lung uptake is significantly higher in preimmunized animals than in untreated animals. The rate of phagocytosis of particles with different surface characteristics has also been studied in vitro with isolated mouse peritoneal macrophages. This technique gives a good correlation with the in vivo results; thus particles with a short half-life in mice are rapidly phagocytosed by the macrophages in vitro.