Biodegradable microspheres. XII: Properties of the crosslinking chains in polyacryl starch microparticles

Polyacryl starch microparticles are under current investigation for use as lysosomotropic drug carriers. This paper describes some in vivo and in vitro properties of the crosslinking polymer chains in these particles. A radioactive label was introduced into the microparticle crosslinks by copolymerization of [14C]acrylamide. It was shown by gel permeation chromatography that the amount of tetramethylethylenediamine (TEMED) used in the microparticle polymerization influenced the molecular weight composition of the hydrocarbon chains. Increasing the TEMED concentration resulted in a higher proportion of shorter polymeric chains. After iv administration to mice, the microparticles were taken up mainly by the liver. Although presumably nonmetabolizable, a slow elimination (terminal half-life of 4-5 months) of the hydrocarbon chains from the liver was observed. This suggests that after exocytosis from the Kupffer cells or after their turnover, dissolved material is taken up by liver parenchymal cells and excreted into the bile.