Particles, rapid expansion supercritical fluid process

Meziani, M. J. and Sun, Y. P. (2003). Protein-conjugated nanoparticles from rapid expansion of supercritical fluid solution into aqueous solution. J. Am. Chem. Soc. 125, 8015-8018. Meziani, M. J., Pathak, P., Hurezeanu, R., Thies, M. C., Enick, R. M., and Sun, Y. P. (2004). Supercritical fluid processing technique for nanoscale polymer particles. Angew. Chem. Int. Ed. Engl. 43, 704—707. 

In our laboratory, we have modified the supercritical fluid processing method known as RESS (Rapid Expansion of Supercritical Solution) (7 J-7S) by expanding the supercritical solution into a liquid solvent, or RESOLV (Rapid Expansion of a Supercritical Solution into a Liquid SOLVent), to produce nanoscale semiconductor and metal particles (7, 9, 19-22). For the solubility of metal salts, supercritical ammonia, THF, and acetone were used in the rapid expansion at relatively higher temperatures. The nanoparticles thus obtained were small (less than 10 nm), with relatively narrow size distributions. In an effort to replace the organic solvents with C02-based systems for RESOLV at ambient temperatures, we used a water-in-C02... 

The routes to particle synthesis via supercritical fluids basically follow two paths. Rapid Expansion of Supercritical Solution (RESS) and Supercritical Anti-Solvent (SAS). The basic processing steps are outlined in Figure 21.18 and Figure 21.19, respectively. RESS involves homogenization of the particles raw material in the supercritical fluid followed by rapid expansion of the solution through an expansion device such as a nozzle. Depending on the nozzle design, time-temperature and time-pressure profiles, and whether one uses... 

Crystallization Solutes may be crystallized from supercritical fluids by temperature and/or pressure changes, and by the PCA process described above. In the rapid expansion from supercritical solution (BESS) process, a SCR containing a dissolved solute is expanded through a nozzle or orifice in less than 1 ms to form small particles or fibers. A variety of inorganic crystals have been formed naturally and synthetically in SCR water. 

By utilizing the rapid expansion of supercritical solutions, small-size particles can be produced from materials which are soluble in supercritical solvents. In this process, a solid is dissolved in a pressurized supercritical fluid and the solution is rapidly expanded to some lower pressure level which causes the solid to precipitate. This concept has been demonstrated for a wide variety of materials including polymers, dyes, pharmaceuticals and inorganic substances. 

A novel fluidized-bed coating process using the rapid expansion of supercritical solutions (RESS) is described for the encapsulation of fine particles [2,3]. This process exploits the capability of supercritical fluids to act as a selective solvent. Supercritical fluids are noteworthy in that their... 

Several new processes for formation of solid particles with defined particle size and particle size distribution using supercritical fluids were developed in the past years. Examples are crystallisation from supercritical fluids, rapid expansion of supercritical solutions (RESS), gas antisolvent recrystallisation (GASR), and PGSS (Particles from Gas Saturated Solutions)-process [1,2]. 

Franck SG, Ye C. Small particle formation and dissolution rate enhancement of relatively insoluble drug using rapid expansion of supercritical solution (RESS) process. Proceedings of the 5th International S5miposium on Supercritical Fluids, 8-12, April, Atlanta, 2000. 

As described in Chapter 3, several SCF techniques are available for the preparation of drug delivery systems. These include rapid expansion of supercritical solutions (RESS), gas antisolvent recrystallization (GAS), supercritical antisolvent recrystallization (SAS), supercritical antisolvent with enhanced mass transfer (SAS-EM), solution-enhanced dispersion by supercritical fluids (SEDS), supercritical fluid nucleation (SFN), precipitation with compressed antisolvent (PCA), and aerosolized supercritical extraction of solvents (ASES). While RESS and SFN involve the expansion of a supercritical fluid solution of a drug to form drug particles, GAS, SAS, SAS-EM, SEDS, PCA, and ASES use a supercritical fluid as an antisolvent to precipitate particles of a drug dissolved in an organic solvent (5). General RESS and GAS processes are further elaborated in Sections 1.1.1 and 1.1.2. 

The optical and scanning electron micrographs presented in this chapter show that the particle size of solid materials, such as polymers, monomers, and intermediate chemicals, can be altered by precipitation from a supercritical fluid solution. The only requirement for carrying out the SCF particle reduction process is that the compound must exhibit some solubility in a supercritical fluid. Because the pressure reduction rates are so rapid during the expansion of the solution, supersaturation ratios can be achieved that are much, much greater than can be achieved by thermal, chemical, or antisolvent precipitation processes. Furthermore, it is conjectured that such rapid nucleation rates can result in the particle formation of some materials with a size distribution or morphology that cannot now be achieved by any other process. 

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