Dense Gas Technology Research Articles

Leather dyeing using a new liposome-based process assisted by dense gas technology

Liposomes are spherical vesicles characterized by a double lipidic layer surrounding an inner aqueous core; they have been employed in several fields, such as pharmaceutical, cosmetic and nutraceutical. In this work another possible application is explored: the deposition of dyes on sheep leather is attempted, using liposomes as dye vehicles to obtain a better adhesion of dye on leather surface. A supercritical assisted method called SuperLip is proposed to load red aniline into liposomes, for leather coloration. Process parameters have been optimized such as dye and lipid concentration in the system, water flow rate for vesicles inner core production and Gas to Liquid Ratio of the Expanded Liquid to control size and particles distributions.Nanometric liposomes of about 150 nm diameter have been obtained, with a red aniline Encapsulation Efficiency (EE) of about 75%; micrometric vesicles of about 2 μm were also produced with EE up to 82%, in order to provide large dimensions for covering macroscopic surfaces. A conventional dyeing method and the new liposomal method were compared in terms of deposition time, and color resistance. Liposomes, produced in this work, speeded up dye deposition from 60 min to 30 min, and resulted in a higher resistance to heat exposure; indeed, a discoloration down to 2.3% was observed using the proposed method and 25.1% using conventional method.

Development of a continuous dense gas process for the production of liposomes

A new process called Continuous Anti-Solvent (CAS) process was developed for the production of liposomes using supercritical CO 2. Unlike the current dense gas technologies, CAS method is a single step and continuous process. Preliminary experiments were conducted in semi-batch mode to determine the most suitable operating conditions (stirring speed = 225 rpm; water/lecithin mass ratio = 21) to ensure an efficient phase mixing in the autoclave. Then, two procedures were developed for the CAS process in the continuous mode. According to the results, the single exit procedure enhances the phase mixing in the autoclave with the formation of a CO 2-in-water emulsion which is a good precursor to liposome formation. Liposomes prepared with the CAS method ( P = 9 MPa; T = 308 K; CO 2 flow rate = 0.3 kg h −1; organic solution flow rate = 240 mL h −1; water flow rate = 180 mL h −1) are spherical and multilamellar with a medium diameter included between 10 and 100 μm.

High pressure gases: Role of dynamic intracellular pH in pasteurization

Certain dense gases, including CO(2) and N(2)O, are known to deactivate food pathogens safely. Complete deactivation requires disabling intracellular metabolic pathways by extracellular processing that causes membrane disruption, irreversible denaturation of proteins, or extraction of cell contents. At present, neither the precise physical and metabolic mechanisms nor their kinetics behind dense gas pasteurization are known. The mechanisms depend strongly on both the organism and the environment and may combine membrane disruption, membrane permeabilization, and altering pH. Herein we elucidate the mechanisms of dense gas inactivation with the aid of a novel approach for measuring intracellular pH (pH(i)) under high gas pressure. Using a pH-sensitive GFP-variant of S. cerevisiae as the probe, we demonstrate that membrane permeabilization by a non-acidic gas, N(2)O, contributes to inactivation but at a rate that is relatively low compared to CO(2). CO(2) not only permeabilizes the membrane but also brings about a rapid drop in pH(i), leading to greater deactivation. Mechanistic understanding is vital to develop safe and effective dense gas technologies for food treatment. Knowledge of pH(i) is also important in other cellular processes, including enzyme activity, gene transcription, and protein synthesis. The GFP technique has been demonstrated to be versatile even under pressure.

Dense Gas Processing of Polymers

There is a growing global awareness about environmental pollution, and many sanctions and sustainable practices have been implemented. In particular, the use of volatile organic compounds (VOCs) is a practice that is being limited and minimized world-wide. These VOCs are not only damaging to the environment, but are also an occupational hazard. The polymer processing industry is known to use VOCs extensively for polymerization, fractionation, plasticization, degradation, extraction and purification. More environmentally-friendly methods to circumvent the use of these toxic and hazardous compounds are being explored. The use of dense gases in polymer processing can respond to the need for more environmentally-friendly industrial processes. Products with high-purity, sterility, and porosity can be achieved using dense gas technology (DGT). Currently, DGT has been used for different aspects of polymer processing including polymerization, micronization, and impregnation. Due to its high solubility in polymers and diffusivity, dense CO2 can penetrate and plasticize polymers, whilst impregnating them with low-molecular weight CO2-soluble compounds. The dense CO2 properties of inertness, non-toxicity, and affinity for various therapeutic compounds are specifically advantageous to the medical and biomedical industries. Biodegradable polymers and other medical-grade polymers have benefited from the application of DGT. The aim of this review was to show the versatility of dense CO2 for polymer processing applications, specifically polymerization, polymer blend preparation, drug loading and sterilization.

The Depressurization of an Expanded Solution into Aqueous Media for the Bulk Production of Liposomes

A new dense gas process for the formation of liposomes has been developed: depressurization of an expanded solution into aqueous media (DESAM). The technique provides a fast and simple process for bulk liposome formation. As an alternative to current dense gas technologies, the DESAM process reduces the pressure requirements for liposome formation. Liposomes with diameters between 50 and 200 nm were formed. For all samples produced using ethanol as the solvent, the average effective diameter ranged from 119 to 207 nm. When chloroform was used as the solvent, the average effective diameter increased to 387 nm. The residual solvent volume fraction in the liposomal product was less than 4% v/v, which is approximately one-quarter of the value reported for some other dense gas liposome formation methods. The liposomal samples were stored after formation at 5 degrees C for up to 8 months, with the average effective diameter and polydispersity increasing by only 13% and 7%, respectively, indicating high stability of the formulations.

Dense Gas Technology and Cyclodextrins: State of the Art and Potential

Dense Gas Technology and Cyclodextrins: State of the Art and Potential

Dense Gas Processing of Micron-Sized Drug Formulations Incorporating Hydroxypropylated and Methylated Beta-Cyclodextrin

Because of their importance in pharmaceutical applications, hydroxypropyl-beta-cyclodextrin and methyl-beta-cyclodextrin have been selected to study the formation of micronized complexes incorporating active pharmaceutical ingredients (APIs) and cyclodextrins (CDs) by dense gas (DG) processing. A single-step DG technique was used as an alternative to conventional methods for the manufacturing of API/CD complexes. The DG technology is highly attractive in the pharmaceutical industry because of its potential to generate micronized particles with controlled particle size distributions at moderate operating conditions. The effect of the aerosol solvent extraction system (ASES) processing on the dissolution performance of naproxen (NPX) was examined. The CDs were produced as microspheres smaller than 3 microm. The coprecipitation of each CD with NPX resulted in the production of microparticles with enhanced dissolution rates. The ASES was operated under mild conditions and generated micron-sized spherical particles that could be of particular interest in formulations for pulmonary delivery. Particular advantages of the technique are that (1) nontoxic solvents are used, and (2) it is suitable for the processing of thermally labile compounds. The proposed process can create opportunities to improve current administration routes and exploit novel delivery systems for drug formulations incorporating CDs.

Dense gas anti-solvent processes for pharmaceutical formulation

Conventional processes for manipulating the characteristics of particles used in drug formulation are limited in their flexibility. Recent studies in which supercritical/dense gas processes have been used for particle design and drug formulation show considerable promise. These developing dense gas technologies for drug formulation are described in this review. Issues relating to scale up on dense gas technology application for pharmaceutical active are also identified.

Current issues relating to anti-solvent micronisation techniques and their extension to industrial scales

Realisation of the potential of dense gas anti-solvent precipitation for commercially viable processing of fine chemicals is hindered by our inability to fully exploit the advantages afforded to dense gases. The feasibility of producing dry uniformly sized micronised material using dense gas technology has been well established on a bench scale. However, translating these advantages to an industrial scale remains a challenge for engineers. In this paper, issues specific to the process scale up of dense gas anti-solvent precipitation are discussed. Anti-solvent precipitation is essentially a mixing process and any predictable increase in production rate is impossible without a thorough understanding of the dominant controlling factors. In this paper the dominant process variables, issues such as safety, cleaning, residual solvent concerns, precipitate sizing and product handling are addressed.

Gravity Currents in the Laboratory, Atmosphere, and Ocean

A gravity or current, is the flow of one fluid within another caused by the density difference between the fluids. The difference in specific weight that provides the driving force may be due to dissolved or suspended material or to temperature differences. Gravity currents are primarily horizontal, occurring as either top or bottom boundary currents, or as intrusions at some intermediate level. The fluids are usually miscible and the mixing that results can play an important part in the dynamics of the flow. Since gravity currents are formed in many different natural situations and may also be man-made, knowledge of their properties is of importance in many scientific disciplines. In the atmosphere, thunderstorm outflows and sea-breeze fronts are gravity currents of relatively cold dense air. Atmospheric-suspension gravity currents include avalanches of airborne snow particles, also fiery avalanches and base surges formed from gases and solids issuing from volcanic eruptions. Gravity currents have important applications in aircraft safety, atmo­ spheric pollution, entomology and pest control, and especially in dense-gas technology. Industrial accidents in which gravity currents may be formed include the spread of a dense gas from an accidental release. In the ocean, gravity currents are driven by salinity and temperature inhomogeneities, or as turbidity currents whose density derives from sus­ pended mud or silt. Lines of foam and debris on the ocean surface may indicate the front of a gravity frequently brought about by tidal processes. The latter also affect the behavior of gravity currents such as river plumes at the surface and salt wedges on a river bed. The important problems related to oil spillage on the sea have been the subject of a review paper in this series (Hoult 1972).