Study of Different Aging Mechanisms in Perfluorocarbon Nanoemulsions

Perfluorocarbon (PFC)-in-water nanoemulsions may serve as synthetic oxygen carriers for different clinical procedures. To prepare these nanoemulsions a biocompatible surfactant as lecithin can be used, forming PFC droplets and liposomes with different particle size. However, the simultaneous presence of liposomes and PFC droplets on global nanoemulsion stability has not been widely studied.

Preliminary observations from nanoemulsion behavior have made possible to identify a sedimentation phenomena as the first instability mechanics, producing two different phases: supernatant and sediment, without nanoemulsion breakage. The aim of this work is to study the evolution of each phase and their influence on global nanoemulsion stability during the time.

Nanoemulsions are prepared with perfluorooctyl bromide 99% (PFOB, Exfluor Research Corp, USA) as dispersed phase and soybean lecithin (Epikuron 170®, DEGUSSA, Germany) as surfactant. Analysis of supernatant and sediment is done following the evolution of: i) particle size distribution, through dynamic light scattering and near infrared (NIR) spectroscopy, ii) rheological behavior, by viscosity changes, and (iii) pH measurements. As reference system a PFC-free dispersion is also prepared and characterized through time.

The results of particle size analysis show a multimodal distribution in both phases. In this distribution, each population and its evolution could be associated to a specific kind of particle by a comparison of supernatant and sediment with the reference system. This behavior is supported by the analysis of NIR spectra, which show difference between droplets and liposomes.

The difference in the evolution of high shear rate viscosity value between supernatant and sediment, allows characterizing macroscale behavior. Finally, there is a pH decrease over time suggesting lecithin oxidation.

In conclusion, in the time supernatant and sediment shall rich in liposomes and droplets respectively, with different aging mechanisms.