solvent and the salting-out agents are then eliminated by cross-flow filtration [61].
Selection of the salting-out agent plays an important role in the encapsulation
efficiency of the drug. To overcome the harmful environmental effects, a modified
version of the emulsion process was evolved by linking it to a salting-out process
[62] to avoid surfactants and chlorinated solvents. An electrolyte-saturated or
nonelectrolyte-saturated aqueous solution containing PVA (stabilizer) was added
to an acetone solution of the polymer under continuous stirring. The saturated
aqueous solution prevented the acetone from mixing with water through the
salting-out process [63]. After formation of an oil-in-water emulsion, water was
added in an adequate amount to allow the complete diffusion of acetone into the
aqueous phase, resulting in formation of nanospheres. PLA nanoparticles were
developed by adding an aqueous gel containing magnesium acetate tetrahydrate
and PVA to an acetone solution of the polymer to form a water-in-oil emulsion [41].
During the mixing of water with acetone, a liquid–liquid two-phase system was
formed due to the presence of the salting-out agent. An oil-in-water emulsion was
obtained on further addition of the aqueous solution followed by the addition of
sufficient water to allow diffusion of acetone into the aqueous phase, resulting in the
formation of nanoparticles with an average size of 295 nm [41]. Recently, poly
(trimethylene carbonate) nanoparticles of size 183 and 251 nm were prepared by
single emulsion and salting-out methods, respectively [64].
5.3 Nanoprecipitation
Nanoprecipitation is also called solvent displacement and is used for the preparation of polymeric nanoparticles [65]. It is a simple, fast and reproducible method
that is broadly employed for the development of both nanospheres and
nanocapsules. The method is based on the interfacial deposition of a polymer
after displacement of a semipolar solvent from a lipophilic solution [66]. Organic
solvents such as ethanol, acetone, hexane, methylene chloride, dioxane, or binary
solvent blend, which are miscible in water and easy to remove by evaporation, are
selected as solvent [67]. The polymers commonly used are biodegradable
polyesters, especially PCL [68, 69], PLA [70], and PLGA [71, 72]. Polymeric
nanoparticles are prepared by slow addition of the organic phase to the aqueous
phase under stirring. In reverse, the addition of the aqueous phase to the organic
phase also leads to the formation of nanoparticles. The physicochemical properties
of polymeric nanoparticles are associated with conditions such as organic phase
injection rate, aqueous phase agitation rate, and the organic phase to aqueous phase
ratio. Surfactant plays an important role in the formation of polymeric nanoparticles
by protecting from agglomeration for nanoprecipitation [68].
Biodegradable Polymers for Potential Delivery Systems for Therapeutics
183
Selection of the salting-out agent plays an important role in the encapsulation
efficiency of the drug. To overcome the harmful environmental effects, a modified
version of the emulsion process was evolved by linking it to a salting-out process
[62] to avoid surfactants and chlorinated solvents. An electrolyte-saturated or
nonelectrolyte-saturated aqueous solution containing PVA (stabilizer) was added
to an acetone solution of the polymer under continuous stirring. The saturated
aqueous solution prevented the acetone from mixing with water through the
salting-out process [63]. After formation of an oil-in-water emulsion, water was
added in an adequate amount to allow the complete diffusion of acetone into the
aqueous phase, resulting in formation of nanospheres. PLA nanoparticles were
developed by adding an aqueous gel containing magnesium acetate tetrahydrate
and PVA to an acetone solution of the polymer to form a water-in-oil emulsion [41].
During the mixing of water with acetone, a liquid–liquid two-phase system was
formed due to the presence of the salting-out agent. An oil-in-water emulsion was
obtained on further addition of the aqueous solution followed by the addition of
sufficient water to allow diffusion of acetone into the aqueous phase, resulting in the
formation of nanoparticles with an average size of 295 nm [41]. Recently, poly
(trimethylene carbonate) nanoparticles of size 183 and 251 nm were prepared by
single emulsion and salting-out methods, respectively [64].
5.3 Nanoprecipitation
Nanoprecipitation is also called solvent displacement and is used for the preparation of polymeric nanoparticles [65]. It is a simple, fast and reproducible method
that is broadly employed for the development of both nanospheres and
nanocapsules. The method is based on the interfacial deposition of a polymer
after displacement of a semipolar solvent from a lipophilic solution [66]. Organic
solvents such as ethanol, acetone, hexane, methylene chloride, dioxane, or binary
solvent blend, which are miscible in water and easy to remove by evaporation, are
selected as solvent [67]. The polymers commonly used are biodegradable
polyesters, especially PCL [68, 69], PLA [70], and PLGA [71, 72]. Polymeric
nanoparticles are prepared by slow addition of the organic phase to the aqueous
phase under stirring. In reverse, the addition of the aqueous phase to the organic
phase also leads to the formation of nanoparticles. The physicochemical properties
of polymeric nanoparticles are associated with conditions such as organic phase
injection rate, aqueous phase agitation rate, and the organic phase to aqueous phase
ratio. Surfactant plays an important role in the formation of polymeric nanoparticles
by protecting from agglomeration for nanoprecipitation [68].
Biodegradable Polymers for Potential Delivery Systems for Therapeutics
183