Emulsification-solvent evaporation technique

The most common technique used for the preparation of PLGA nanoparticles is the emulsification-solvent evaporation technique. This technique allows the encapsulation of hydrophobic drugs and consists of dissolving the polymer and the compound in an organic solvent. The emulsion oil (O) in water (W) is prepared by adding water to a polymer solution. The nanosized droplets are induced by sonication or homogenization. The solvent is then evaporated or extracted and the nanoparticles collected after centrifugation [69,70]. 

Watts, P. J., Davies, M. C., and Melia, C. D. Microencapsulation using emulsification/ solvent evaporation An overview of techniques and applications. Crit. Rev. Ther. Drug Carrier Syst. 7(3) 235-259, 1990. 

Emulsion Solvent Evaporation The basic concept of the emulsion solvent evaporation technique producing nanoparticles is very straightforward. The particles are formed as an emulsion of a polymer-surfactant mixture and dispersed in an organic solvent. The solvent is then evaporated to leave behind the individual emulsion droplets which form stable free nanoparticles [203], This method is far easier and more preferable over methods such as spray drying and homogenization and operates under ambient conditions and mild emulsification conditions. The size and composition of the final particles are affected by variables such as phase ratio of the emulsion system, organic solvent composition, emulsion concentration, apparatus used, and properties of the polymer [204],... 

CS-based thiolated microgels with an average size of 18 pm have been prepared either by water-in-oil (w/o) emulsification solvent evaporation" or by precipitation-miaonization technique." For thiolation, 2-iminothiolane (Trout s rea nt) was covalently linked to CS via an amidine bond leading to the formation of CS-4-thiobutylamidine. Such polymers show higher mucoadhesive and permeation-enhandng properties than unmodified CS," " which makes them ideal precursors for nasal or oral dmg delivery systems. 

Liu, R., Ma, G.H., Meng, F.-T., and Su, Z.-G., Preparation of uniform-sized PLA microcapsules by combining Shirasu Porous Glass membrane emulsification technique and multiple emulsion-solvent evaporation method, J. Contrail. Ret, 103, 31, 2005. 

A technique based on the formation of a multiple emulsion with an external aqueous phase was developed for the encapsulation of water-soluble drugs in order to replace the external oil phase. Possible unwanted interactions between the oil and the emulsified wax such as swelling or dissolution of the wax, clean-up requirements of the final product, and recovery of the oil phase could be eliminated. In analogy to the encapsulation of water-soluble drugs within polymeric microparticles by a w/o/w-solvent evaporation method, a molten wax phase was used instead of an organic polmer solution. A heated aqueous solution of pseudoephedrine HCl was emulsified into the molten carnauba wax, followed by the emulsification of this w/o-emulsion into a heated external aqueous phase. The temperature of the internal and external aqueous phases had to be kept above the melting temperature of the wax in order to avoid premature... 

Preparation of microsphere with electrospraying technique produces smaller size microsphere more easily when compared to the emulsification and solvent evaporation methods. 

Nanoparticle fabrication includes methods such as solvent evaporation, spontaneous emulsification, solvent diffusion, salting out/emulsification diffusion, and polymerization techniques [24]. The synthesis method can greatly impact the particle s physical, chemical, and biological properties and the dispersion and stability of the particles, which are important considerations in biomedical applications. The nanoparticle size and shape is of great importance because the internalization, circulation, distribution, and targeting aspects of the system can be affected by these characteristics [5]. 

Liu R, Ma GH, Wan YH, Su ZG. 2005a. Influence of process parameters on the size distribution of PLA microcapsules prepared by combining membrane emulsification technique and double emulsion-solvent evaporation method. Colloids Surf B 45 144-153. 

One of the major drawbacks of liposomes is related to their preparation methods [3,4]. Liposomes for topical delivery are prepared by the same classic methods widely described in the literature for preparation of these vesicles. The majority of the liposome preparation methods are complicated multistep processes. These methods include hydration of a dry lipid film, emulsification, reverse phase evaporation, freeze thaw processes, and solvent injection. Liposome preparation is followed by homogenization and separation of unentrapped drug by centrifugation, gel filtration, or dialysis. These techniques suffer from one or more drawbacks such as the use of solvents (sometimes pharmaceutically unacceptable), an additional sizing process to control the size distribution of final products (sonication, extrusion), multiple-step entrapment procedure for preparing drug-containing liposomes, and the need for special equipment. 

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