RESS rapid expansion of supercritical fluid

Micro-encapsulation of drug-polymer systems using flic RESS (Rapid Expansion of Supercritical Fluid Solutions) techniques have been initiated with limited success due to poor understanding of the complex phenomena involved in co-nucleation of components. Not only do the particles have to be nucleated with the desired particle size and shape but also encapsulate the material simultaneously in an uniform fashion. 

RESS [Rapid Expansion of Supercritical Solutions] A process for depositing a film of solid material on a surface. The substance is dissolved in supercritical carbon dioxide. When the pressure is suddenly reduced, the fluid reverts to the gaseous state and the solute is deposited on the walls of the vessel. Used for size-reduction, coating, and microencapsulation. First described in 1879. Developed in 1983 by R. D. Smith at the Battelle Pacific Northwest Laboratory. 

The magnetic metals were also prepared by a method [25] based on the rapid expansion of supercritical fluid solutions (RESS) coupled with chemical reduction to produce nickel, cobalt, iron, and iron oxide nanopartides of reasonably narrow size distribution. Under the protection of a polymer stabilization agent, the largely amorphous metal nanopartides form stable suspensions in room-temperature solvents. 

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... 

Homogeneous precipitation of particles from supercritical solvents (rapid expansion of supercritical fluids (RESS)). Applications are microparticles for pharmaceutics [45]. 

Depolymerization, e.g., polyethylene terephthalate and cellulose hydrolysis Hydrothermal oxidation of organic wastes in water Crystallization, particle formation, and coatings Antisolvent crystallization, rapid expansion from supercritical fluid solution (RESS)... 

A number of techniques are based on supercritical fluid technology. Three are of particular pharmaceutical interest, namely the supercritical antisolvent (SAS) system, the rapid expansion of supercritical solution (RESS) method, and the gas antisolvent (GAS) technique [126]. 

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]. 

The rapid expansion of supercritical solutions (RESS) was explored by several authors as a novel route to the formation of microparticles. Ohgaki [1] produces fine stigmasterin particles by the rapid expansion of a supercritical C02 solution. Amorphus fine particle and whisker-like crystals (0,05 - 3 pm) were obtained with different preexpansion pressures. Johnston [2] obtained submicron particles from different polymers. Loth [3] described the mirconisation of phenacetin with supercritical fluids. 

The supercritical fluid mefhod is a relafively new method, which can minimize the use of organic solvents and harsh manufacturing conditions taking advantage of two distinctive properties of supercritical fluids (i.e., high compressibility and liquid-like density). This method can be broadly divided into two parts rapid expansion of supercritical solutions (RESS), which utilizes the supercritical fluid (e.g., carbon dioxide) as a solvent for the polymer, " and supercritical antisolvent crystallization (SAS), using the fluid as an antisolvent that causes polymer precipitation. Recent reviews of the supercritical technology for particle production are available in the literature. ... 

Turk, M. Hils, P. Helfgen, B. Schaber, K. Martin, H.-J. Wahl, M.A. Micronization of pharmaceutical substances by the Rapid Expansion of Supercritical Solutions (RESS) a promising method to improve bioavailability of poorly soluble pharmaceutical agents. J. Supercrit. Fluids 2002, 22 (1), 75-84. 

The first supercritical fluid-based micronization process has been the rapid expansion of supercritical solutions (RESS) it is based on the solubilization of the solid to be micronized in the SCF and its subsequent precipitation by fast depressurization of the solution. However, the use of this technique is largely limited by the low solubility in supercritical carbon dioxide (SC-CO2) of many of the solids of interest. " ... 

Supersaturation of solutions to precipitate ceramic powders is attained by means of supercritical fluids. This technique, termed rapid expansion of supercritical solutions (RESS), is reviewed elsewhere. ... 

The rapid expansion of supercritical solution (RESS) process consists of dissolving the product in a supercritical fluid (usually carbon dioxide) and then rapidly depressurizing the solution through a spray nozzle thus causing extremely rapid nucleation of the product into a highly dispersed material. Various technologies based on supercritical fluids are given in Table 5.5. 

Precipitation from supercritical solutions composed of supercritical fluid and solute(s). Rapid expansion of supercritical solutions, the RESS... 

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. 

---