A dynamic light scattering study of the influence of the phospholipid concentration in a model perfluorocarbon emulsion

Small-scale preparation of perfluorocarbon-nanoemulsions utilizing dual centrifugation

BACKGROUND

Perfluorocarbon-nanoemulsions (PFC-NE) made of PFC and phospholipids (PL) by homogenization are optimal for in vivo-¹⁹F labelling of monocytes and subsequently of inflamed tissues in magnetic resonance imaging (MRI). Necessary requirements for in vivo use of PFC-NE are sterility, suitable droplet sizes and the absence of immune activating liposomes, which are a typical byproduct of the homogenization process.

METHODS AND RESULTS

To meet these requirements, we developed an aseptic in-vial preparation technique for PFC-NE based on dual centrifugation (DC) by testing different PFC/phospholipid ratios as well as the application of additives. Two different PFC, perfluorooctylbromide (PFOB) and perfluoro-15-crown-5-ether (PFCE), were investigated. Particle sizes were assessed by dynamic light scattering and NE morphology by cryoTEM. DC homogenization was optimal when using an excess of PL (8.7 % (m/m) of utilized PFC, z-ave: 180 nm, pdi: 0.2). A purification approach by centrifugation was implemented to remove liposomes formed from the excess of PL during homogenization. The purification success was proven by phospholipid assay and PFC quantification via density and sound velocity measurements.

CONCLUSION

DC in combination with a short centrifugation is a fast and reliable way of small-scale aseptic PFC-NE production for ¹⁹F MRI passive-targeting experiments of monocytes and inflamed tissues.

Investigating perfluorohexane particles with high-frequency ultrasound

Submicron particles filled with liquid perfluorocarbon are currently being studied as a potential ultrasound-targeted contrast agent. The objective of this study was to evaluate the scattering properties of these particles. Sets of perfluorohexane-filled particles of different average sizes (300 nm to 1000 nm) were produced with a constant total volume fraction. The attenuation coefficient was measured in the 15- to 50-MHz frequency range and was found to increase smoothly with frequency and to be independent of the amplitude and bandwidth of the transmitted pulse. The values range from 0.31 to 0.64 dB/mm at 30 MHz for mean particle size ranging from 970 to 310 nm, respectively. The backscattering spectra of the particle solutions were measured and showed no sign of nonlinear scattering. The backscattering coefficient increased with the power 3.9 +/- 0.3 of the frequency. These results confirm that liquid perfluorocarbon droplets behave as linear Rayleigh scatterers.

Liposomal incorporation of Artemisia arborescens L. essential oil and in vitro antiviral activity

The effect of liposomal inclusion on the in vitro antiherpetic activity of Artemisia arborescens L. essential oil was investigated. In order to study the influence of vesicle structure and composition on the antiviral activity of the vesicle-incorporated oil, multilamellar (MLV) and unilamellar (SUV) positively charged liposomes were prepared by the film method and sonication. Liposomes were obtained from hydrogenated (P90H) and non-hydrogenated (P90) soy phosphatidylcholine. Formulations were examined for their stability for over one year, monitoring the oil leakage from vesicles and the average size distribution. The antiviral activity was studied against Herpes simplex virus type 1 (HSV-1) by a quantitative tetrazolium-based colorimetric method. Results showed that Artemisia essential oil can be incorporated in good amounts in the prepared vesicular dispersions. Stability studies pointed out that vesicle dispersions were very stable for at least six months and neither oil leakage nor vesicle size alteration occurred during this period. After one year of storage oil retention was still good, but vesicle fusion was present. Antiviral assays demonstrated that the liposomal incorporation of A. arborescens essential oil enhanced its in vitro antiherpetic activity especially when vesicles were made with P90H. On the contrary, no significant difference in antiviral activity was observed between the free and SUV-incorporated oil.