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Chemically simplified lipid mixtures are used here as models of the cell plasma membrane exoplasmic leaflet. In such models, phase separation and morphology transitions controlled by line tension in the liquid-disordered (Ld) + liquid-ordered (Lo) coexistence regime have been described [1]. Here, we study two four-component lipid mixtures at different cholesterol fractions: brain sphingomyelin (BSM) or 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC)/1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC)/1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC)/cholesterol (Chol). On giant unilamellar vesicles (GUVs) display a nanoscopic-to-macroscopic transition of Ld + Lo phase domains as POPC is replaced by DOPC, and this transition also depends on the cholesterol fraction. Line tension decreases with increasing cholesterol mole fractions in both lipid mixtures. For the ternary BSM/DOPC/Chol mixture, the published phase diagram [19] requires a modification to show that when cholesterol mole fraction is >~0.33, coexisting phase domains become nanoscopic.

Organic solvent residues are always a concern with the liposomes produced by traditional techniques. Our objectives were to encapsulate hydrophilic and lipophilic compounds in liposomes using a newly designed supercritical fluid process coupled with vacuum-driven cargo loading. Supercritical carbon dioxide was chosen as the phospholipid-dissolving medium and an ecofriendly substitute for organic solvents. Liposomal microencapsulation was conducted via a 1000-μm expansion nozzle at 12.41MPa, 90°C, and aqueous cargo loading rate of 0.25ml/s. Vitamins C and E were selected as model hydrophilic and lipophilic compounds encapsulated in the integrated liposomes. The average vesicle size was 951.02nm with a zeta potential of -51.87mV. The encapsulation efficiency attained was 32.97% for vitamin C and 99.32% for vitamin E. Good emulsion stability was maintained during storage at 4°C for 20days. Simultaneous microencapsulation in the liposomes was successfully achieved with this supercritical fluid process.

A new technique of liposomal microencapsulation, consisting of supercritical fluid extraction followed by rapid expansion of the supercritical solution and vacuum-driven cargo loading, was successfully developed. It is a continuous flow-through process without usage of any toxic organic solvent. For use as a coating material, the solubility of soy phospholipids in supercritical carbon dioxide was first determined using a dynamic equilibrium system and the data was correlated with the Chrastil model with good agreement. Liposomes were made with D-(+)-glucose as a cargo and their properties were characterized as functions of expansion pressure, temperature, and cargo loading rates. The highest encapsulation efficiency attained was 31.7% at the middle expansion pressure of 12.41MPa, highest expansion temperature of 90°C, and lowest cargo loading rate of 0.25mL/s. The large unilamellar vesicles and multivesicular vesicles were observed to be a majority of the liposomes produced using this eco-friendly process.

Background Liposomes are spherical phospholipid vesicles with the capability of versatile microencapsulation of hydrophilic and lipophilic compounds. Organic solvent residue has always been a concern in conventional methods of liposome generation. Scope and approach Dense gas techniques using supercritical carbon dioxide as the phospholipid-dissolving agent can provide a green solution for reduction or avoidance of organic solvent use. Key findings and conclusions In this review, conventional and dense gas processes of liposomal microencapsulation are evaluated. Comprehensively understanding the current progress of supercritical fluid techniques for liposomal microencapsulation will be helpful for development of a non-toxic continuous process of this application in the food and related industries.

Citronellal and methyl anthranilate (MA) are both nonpolar molecules with similar physical properties except for their molecular structures. The solubility of citronellal in supercritical carbon dioxide (SC-CO2) was measured using a static equilibrium system in the pressure range of (9.1 to 14.2) MPa and at (313.15 and 333.15) K. For MA, (9.1 to 24.3) MPa was used at the same temperatures. Solubility data of citronellal and MA in SC-CO2 were well correlated using the Chrastil equation and Peng–Robinson equation of state. Under comparable operating conditions, the linear-chained citronellal solubility in SC-CO2 was three to four times higher than its aromatic derivative MA. The acentric factor of citronellal (ω = 1.004) is higher than that of MA (ω = 0.577), indicating that citronellal has larger molecular asymmetry. This difference allows less intermolecular binding energy but gives higher vapor pressure to citronellal, making it more readily soluble in SC-CO2. The results suggest that the acentric factor...

To better understand animal cell plasma membranes, we studied simplified models, namely four-component lipid bilayer mixtures. Here we describe the domain size transition in the region of coexisting liquid-disordered (Ld) + liquid-ordered (Lo) phases. This transition occurs abruptly in composition space with domains increasing in size by two orders of magnitude, from tens of nanometers to microns. We measured the line tension between coexisting Ld and Lo domains close to the domain size transition for a variety of lipid mixtures, finding that in every case the transition occurs at a line tension of ∼0.3 pN. A computational model incorporating line tension and dipole repulsion indicated that even small changes in line tension can result in domains growing in size by several orders of magnitude, consistent with experimental observations. We find that other properties of the coexisting Ld and Lo phases do not change significantly in the vicinity of the abrupt domain size transition.

Supercritical fluid technology has emerged as a cost-effective and low-hazard alternative to solvent-based methodologies in polymer synthesis, pharmaceutical science, and related biomedical applications. In this review, we first briefly describe the distinctive features of a supercritical fluid, biodegradable polyesters, and lipases. We will then cover the latest progress of supercritical fluid technology in polymerization. Lipase-catalyzed polymerization in supercritical carbon dioxide (SC−CO2) will be the focus of the synthesis section. The last section presents the biomedical applications employing SC−CO2 polymerization, including microcapsule formation for drug delivery, microcellular scaffold fabrication, and SC−CO2-assisted processes for polymer-based treatments, such as surface functionalization, aerogel formation, and fine particle formation. Each topic is illustrated with the most successful examples. Understanding the current progress in SC−CO2 polymerization is an essential step to facilitate the exploration with this green technology in new research frontiers.

The solubility of methyl anthranilate in supercritical carbon dioxide was determined using dynamic and static equilibrium systems. Three temperatures (40, 60 and 80 °C) and a pressure range between 160 and 340 atm were applied for the dynamic solubility measurements. The flow rate was maintained at 0.5 mL min−1 in the dynamic solubility measurements, where the solute solubility was claimed to be independent of the flow-rate factor. Two temperatures (40 and 60 °C) and the pressure range between 100 and 265 atm were used in the static equilibrium system. The crossover pressure region was observed between 220 and 240 atm in the static system, but was not seen in the dynamic system. The solubility of methyl anthranilate determined by the static system was consistently higher than the dynamic solubility measurement, indicating that the static technique provided more reliable solubility data for methyl anthranilate than the dynamic technique. The solubility data obtained with the static system were in good agreement with the predictive models based on the Chrastil equation and the Peng–Robinson equation of state with the Panagiotopoulos and Reid mixing rule. Copyright © 2006 Society of Chemical Industry

When phospholipid bilayers have coexisting liquid disordered (Ld) and liquid ordered (Lo) phases, Ld/Lo line tension has strong control over the size of the coexisting liquid domains. In order to minimize light-induced artifacts that involve lipid reactivity, we chose a lipid mixture with minimal double bonds, DSPC, diphytanoyl-PC, DLPC, and cholesterol. Giant unilamellar vesicles (GUVs) were generated using the electroswelling technique and visualized with an inverted fluorescent microscope. Line tension was determined from the boundary fluctuations between Ld and Lo domains using Flicker Spectroscopy. The Ld/Lo line tension is measured for different GUV compositions within the Ld + Lo coexistence region. The ratio of diphytanoyl-PC and DLPC is then adjusted to control the size of coexisting domains. Different fluorescent dyes are compared to find the minimal light-induced artifacts during the line tension measurements. The results presented in this study provide a more detailed picture of how a cell might control lipid raft size.