Solvent Deposition or Nanoprecipitation

Solvent deposition or nanoprecipitation describes the formation of nanocapsules or nanoparticles by dissolution of poly(lactic acid) or a poly(lactic acid)-copolymer in a water miscible organic solvent, such as acetone [145-147] or benzyl alcohol [148]. Again the drug is dissolved in or admixed to the organic solution. This mixture is then poured into a surfactant-containing water phase under moderate stirring. Surfactants that can be used include polox-amers 118, 407, poloxamine 904, 908, and 1504, or stabilizing hydrocolloids such as poly(vinyl alcohol) or gelatin. The aqueous phase turns opalescent due to the formation of nanocapsules [145]. The acetone or a similar water miscible organic solvent is then removed similarly to solvent evaporation. Besides polylactic acid and copolymers, other polymers such as poly(e-caprolactone) [148-150], EudragitĀ® [148] or another methyl methacrylic acid copolymer [151], poly(6-malic acid-cobenzyl maleate) [152], or cellulose acetate phthalate [153] can be used, and by using acetonitrile as the organic solvent even no surfactants are required [151].

The process of precipitation-solvent evaporation can be modified by addition of the organic phase into a electrolyte rich aqueous solution. The electrolyte leads to the salting out of the organic materials and to the formation of nanoparticles after addition of water which results in the extraction of the water miscible organic solvent [153-157].

The solvent deposition method also may be called nano-precipitation, solvent displacement, or the precipitation-solvent evaporation method.

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