Sample Solution

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].
PNP characteristics are influenced by the nature and concentration of their components [162, 164]. The key variables determining the success of the method and affecting the physicochemical properties of the PNP are those associated with the conditions of adding the organic phase to the aqueous phase, such as organic phase injection rate, aqueous phase agitation rate, the method of organic phase addition and the organic phase to aqueous phase ratio.
Lince et al.,2008 [175] indicated that the process of particle formation in the nanoprecipitation method includes three stages: nucleation, growth and aggregation. The separation between the nucleation and the growth stages is the key factor for formation of uniform particles. Ideally, operating conditions should allow a high nucleation rate strongly dependent on super saturation and low growth rate.

Nanoprecipitation method has some advantages over other method used for preparation of nanoparticles, which include that: (1) Major advantage of this method is the use of the solvents (Acetone/Ethanol) which are considered to be less toxic than water- immiscible solvents like dichloromethane and chloroform, (2) in this method, nanoparticles are formed spontaneously with high shear , (3) Further purification is not required because of the surfactant and solvent and (4) it is a simple, fast and reproducible method which is commonly used for the preparation of both nanocapsules and nanospheres.
The solvent displacement technique can be used to formulate nanocapsules by