Emulsification solvent extraction evaporation method

Figure 11.1 Schematic of water-inoil-in-water (W1/OAV2) emulsification solvent extraction/ evaporation method.

State compared to in the dissolved state [58]. Properties of the drug such as its hydro-phihcity or hydrophobicity and whether it is easily denatured are usually key determinants of which emulsification solvent extraction/evaporation method to use for a particular drug. 

The porosity (ie, pore size and amount of pores) of microparticles is also an important characteristic to take into consideration when fabricating microparticles because it plays an essential role in controlling the release of payloads. The porosity and morphology of particles are usually determined by scanning electron microscopy (SEM). For the emulsification solvent extraction/evaporation method of fabrication, the rate of solvent extraction, which depends on the flow in the stirred vessel the droplet size the temperature and the dispersed phase hold-up in the 0/W emulsion have an effect on porosity [87]. The porosity usually increases with a decrease in solvent extraction rate. The porosity of microparticles results in initial burst release due to pore diffusion [78,88]. Mao et al. studied the influence of different W/O/W emulsification solvent extraction/evaporation process parameters on internal and external porosity of PLGA microparticles [78]. The surface morphology of the microparticles can be influenced by the type of polymer, internal aqueous phase voliune (Wi), volume of continuous phase (W2), polymer concentration, homogenization speed, and equipment used for the primary emulsion [78,79]. 

The ioxilan carbonate particles were prepared as a contrast medium by solvent extract/ evaporation method. The preparation involved emulsification of a methylene chloride solution of the carbonate, removal of solvent, and washing and sizing the particles. The iodine content of the particles was 45%. The average diameter of the ioxilan carbonate particles was 1.1 pm, 95%of them ranging from 0.6 and 2.0 jam. Electron microscopy showed the particle surface to be smooth, and the particles showed practically no aggregation when mixed with rat plasma. The LDgo value for the ioxilan carbonate particles was 1.4 g I/kg for... 

The number average diameter of microspheres obtained from polymers synthesized, by emulsification of polymer solutions followed by solvent extraction and/or solvent evaporation methods, can be controlled by choosing the appropriate conditions at which particles are produced. However, by this method particles with 15 p,m and with D D > 1.9 are produced. Spray drying did not provide poly(L-Lc) particles with regular spherical shape. Direct synthesis of poly(L-Lc) microspheres by ring-opening polymerization with stepwise monomer addition can be used as a method of choice for the production of microspheres with diameters controlled to ca. 6 p.m and with diameter polydispersity parameter < 1.20. 

The pharmaceutical field is among those most widely exploiting ultrasonic emulsification (mainly for the preparation of emulsion-based drugs). Thus, US emulsification has been recently used to prepare biodegradable nanoparticles that can in turn be used to obtain drug-loaded biodegradable microspheres. The method involves ultrasonic emulsification in a continuous flow system to obtain suspended nanoparticles, followed by collection of the particles, solvent extraction and evaporation [49]. 

Microcapsules of PCL and its copolymers may be prepared by aircoating (fluidized bed), mechanical, and, most commonly, solution methods. Typically, the solution method has involved emulsification of the polymer and drug in a two-phase solvent-nonsolvent mixture (e.g., CH2Cl2/water) in the presence of a surfactant such as polyvinyl alcohol. Residual solvent is removed from the tnicrocapsules by evaporation or by extraction (70). Alternatively, the solvent combination can be miscible provided one of the solvents is high-boiling (e.g., mineral spirits) phase separation is then achieved by evaporation of the volatile solvent (71). The products of solution methods should more accurately be called microspheres, for they... 

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