Rapid Expansion Of Supercritical Solutions Research Articles

Application of supercritical fluids for the production of sustained delivery devices

Supercritical fluids are attractive as vehicles for the formation of particles of biomedical interest. We review two novel techniques: the rapid expansion of supercritical solutions for the formation of solvent-free, drug-loaded, injectable microspheres, and the gas anti-solvent precipitation process for the formation of ultrafine and biologically active protein powders.

Rapid expansion of supercritical solutions (ress ): fundamentals and applications

Abstract The rapid expansion of supercritical solutions is a promising new technology for particle formation. The absence of liquid organic solvents, the mild processing temperatures, and the purity of the final product make this process particularly attractive for biomedical applications. In our laboratory, the technique has been used to produce bioerodible polymeric microspheres loaded with a therapeutic drug, a composite suitable for controlled delivery applications. The mathematical modelling of nucleation and growth during the expansion process is useful both in the interpretation of experimental observations, and as a guide for the identification of process conditions leading to unimodal particle size distributions.

超臨界流体 超臨界流体の材料製造・加工への応用

This paper provides an overview of the applications of supercritical fluid technologies to the production and the processing of materials. The novel physical and chemical properties of supercritical fluids are related to their use as extraction solvents, crystallization solvents and reaction media. Supercritical debindering or drying technologies aviod cracks and shrinkage of molded porous materials. The RESS (rapid expansion of supercritical solutions) method, the GAS (gas antisolvent) recrystallization method and hydrothermal processes provide techniques for producing fine uniform powders, thin films and fibers of widely varying materials.

超臨界水溶液から得られる不思議な微粉

Fine silica particles have been produced by the rapid expansion of supercritical water - SiO2 solutions (RESS) at temperatures of 723 and 823 K and pressures from 50 to 100 MPa. New spherical particles sprouting whiskers have also been discovered in the autoclave after the RESS. The solubility of solids in supercritical fluids is a very sensitive function of temperature and pressure. Small changes of pressure result in large changes in density and solvent power, because supercritical fluids are highly compressible. Thus, the rapid expansion of supercritical solutions can give rise to very large supersaturation ratios. Nucleation rates are determined by the competition among solvent expansion, cooling due to depressurization, and high supersaturation. In order to control the product morphology, the effects of experimental parameters, such as preexpansion temperature and pressure, solute concentration, depressurization schemes, nozzle configuration, and sampling method on the product characteristics of materials, have been investigated by means of scanning electron microscopy and X-ray diffraction analysis. It is found that the control of particle size distribution is possible by regulating supersaturation ratio as well as suitable selection of preexpansion temperature and pressure. Unique features of the RESS process are discussed.

Formation of bioerodible polymeric microspheres and microparticles by rapid expansion of supercritical solutions.

Polyhydroxy acids [poly(L-lactic acid) (L-PLA), poly(D,L-lactic acid) (DL-PLA), and poly-(glycolic acid) (PGA)], biocompatible and bioerodible polymers that are being investigated for controlled delivery of pharmaceuticals and are approved by the Food and Drug Administration for in vivo sutures and bone repair implants, have been dissolved in supercritical CO2 and precipitated by rapid expansion of the resulting supercritical solutions (RESS). The formation of these microparticles and microspheres is a first step toward the goal of producing, in a single processing step, drug-loaded polymeric microspheres for use in controlled release applications. Nucleation of poly(L-lactic acid) from CO2 and CO2-acetone mixtures produced microparticles and microspheres ranging from 4 to 25 microns. Microspheres (2-20 microns) were also obtained with chlorotrifluoromethane as solvent. Commercial L-PLA precipitated after extraction of low molecular weight oligomers showed degradation kinetics similar to that of the starting material. The precipitation of DL-PLA from CO2 produced irregular-sized particles (10-20 microns). PGA, a polymer insoluble in most organic solvents, was found to be soluble in supercritical CO2. Nucleation of PGA from CO2 produced both regular-sized particles and needles of 10-40-microns length. The total solubility of commercial L-PLA in supercritical CO2 at 250 bar and 55 degrees C decreased from 0.14 wt % to less than 0.05 wt % and then leveled off as the cumulative flow of CO2 per unit mass of L-PLA loaded in the extractor increased beyond 20 standard L of CO2/g of L-PLA. Use of acetone (1 wt %) as a cosolvent increased L-PLA solubility by approximately 500%.

Particle formation with supercritical fluids—a review

The rapid expansion of supercritical solutions (RESS) is a new and promising method of particle formation. The distinguishing features of this process are the fast attainment of uniform conditions and of high supersaturations in the carrier fluid, which favor the formation of small, monodisperse particles. The technique has been applied to inorganic, organic, pharmaceutical, and polymeric materials. RESS can be used to comminute shock-sensitive solids, to produce intimate mixtures of amorphous materials, to form polymeric microspheres, and to deposit thin films. In this paper, we discuss the fundamentals, experimental methods, applications, and available results from studies of particle formation with supercritical solutions.

Production of powders and films by the rapid expansion of supercritical solutions

A new process utilizing the rapid expansion of supercritical fluid solutions (RESS) is described for the production of fine powders and thin films by the rapid nonequilibrium precipitation of nonvolatile compounds from dense gas solutions upon expansion. A variety of the fluid solution expansion parameters, including solute and solvent identity, solute concentration, expansion temperature, and expansion nozzle configuration, has been shown to affect the product characteristics of materials formed during the RESS process. Conditions favouring thin film formation include very dilute solutions and short nozzles minimizing residence time during expansion. Particle formation is favoured by more concentrated solutions. The process has been demonstrated to produce products of widely varying morphology by the adjustment of RESS parameters, and examples of SiO2 GeO2 and various polymeric materials are presented. Unique features of the RESS process relevant to other powder and film production methods are described and potential applications are discussed.

Formation of Silica Powders from the Rapid Expansion of Supercritical Solutions

Formation of Silica Powders from the Rapid Expansion of Supercritical Solutions