nanoparticles. The level of interest in nanoprecipitation waned for some decades, and the method regained recognition in the 50’s as a means of preparing colloids for stabilizing pigments [142], as well as industrially important components in paints, lacquers, and other coatings [142], While it had already been reported at least as early as the 1940’s as a way for isolation of purified analytical samples of synthetic polymers , nanoprecipitation regained a heightened level of patent interest in the 1950’s and 60’s this time as a cost effective method for purifying synthetic polyolefins [142].
In the late 80’s and early 90’s, Fessi et al.,1989 [143] patented the nanoprecipitation method as a procedure for the preparation of eligible colloidal systems of a polymeric substance in the form of nanoparticles [143].
Nanoprecipitation is also called solvent displacement method or interfacial precipitation method [143-148] .It depends on the precipitation of a preformed polymer from an organic solution and the diffusion of the organic solvent in the aqueous phase either in the presence or absence of a surfactant [143, 149-151].
The main principle of this technique is based on the interfacial deposition of a polymer after displacement of a semi polar solvent, miscible with water, from a lipophilic solution. Rapid diffusion of the solvent into non-solvent phase results in the decrease of interfacial tension between the two phases, which increases the surface area and causes the formation of small droplets of organic solvent [143, 152].
Nanoprecipitation system composed of three basic components: the polymer (synthetic, semi synthetic or natural), the polymer solvent and the non-solvent of the polymer. Organic solvent (i.e., Ethanol, acetone, hexane, methylene chloride or dioxane) which is miscible in water and can be easily removed by evaporation is chosen as polymer solvent. Because of this reason, acetone is considered to be the most commonly used polymer solvent in this method [143,153, 154].
Sometimes, it consists of binary solvent blends, acetone with small volume of water [155], blends of acetone with ethanol [156-158] and methanol [159].
The polymers commonly used are biodegradable polyesters, especially poly (Ɛ-caprolactone) (PCL) [160-164], polylactide (PLA) [165, 166] and poly (lactide-co-glycolide) (PLGA) [167, 168]. Eudragit [156] can also be used as many other polymers such as polyalkylcyanoacrylate (PACA) [169-171].
Natural polymers such as allylic starch [172], dextran ester [173], were also used ,though synthetic polymers have higher purity and better reproducibility than natural polymers [174]. On the other hand, some polymers are PEG copolymerized in order to decrease nanoparticle recognition by the reticular endothelial system [159].
