Intravenously Administered Particles

The organ distribution of intravenously administered particles is determined by particle size, shape, and surface properties such as charge and hydrophobicity. Firstly, to

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Encyclopedia of Nanoscience and Nanotechnology Edited by H. S. Nalwa Volume 10: Pages (83-94)

circulate through the smallest capillaries, the particle size should be less than 5 ^m, and, to avoid spleen filtering effects, the diameter should be less than 200 nm [4]. However, a small size is not sufficient to confer a long blood half-life. For example, tiny polystyrene nanospheres (60 nm in diameter) disappear from blood within minutes [5]. Similar short blood half-lives have been observed with other types of nanoparticles: albumin [6], poly(lactic acid) (PLA) [7], poly(lactic-co-glycolic acid) (PLGA) [8, 9], and poly(cyanoacrylate) [10], which all were rapidly cleared from blood and accumulated at tissue sites, especially liver and spleen. Indeed, the actively endocytic cells of the MPS play a key role in recognizing as foreign and efficiently clearing injected particles from blood. In particular, given its abundant blood flow, tortuous circulation in the sinusoids and efficacy and abundance of the avidly phagocytic Kupffer's cells, liver is an extremely efficient organ for the removal of injected particles. Under these conditions, it only is possible to deliver drugs to MPS organs and it is not possible to fulfill the aims presented in the introduction.

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