Lipid transfer in oil-in-water isasome emulsions: influence of arrested dynamics of the emulsion droplets entrapped in a hydrogel.

The transfer kinetics of lipids between internally self-assembled droplets of O/W emulsions is studied. The droplets (isasomes) consist of various liquid-crystalline phases or W/O microemulsions stabilized by a polymeric stabilizer F127. The various internal phases were identified by the relative peak positions in the small-angle X-ray scattering (SAXS) curves. An arrested system composed of isasomes embedded in a gel matrix actually provides an additional possibility to control these systems in terms of the release of various host molecules. These experiments have been applied to examine the kinetics of the internal phase reorganization imposed by the lipids' release and uptake by the droplets embedded in a κ-carrageenan (KC) hydrogel network. Increasing the concentration of the gelling agent slows down the transfer from one droplet to the other through the aqueous phase. We examined the region where the free diffusion is stopped. i.e., the point where the system changes from the ergodic to the nonergodic state and the kinetics is essentially slowed down. This effect can be balanced by the addition of small amounts of free polymeric stabilizer, which speeds up the kinetics. This is even possible in the case of highly arrested dynamics of the emulsion droplets, as found for the highest KC hydrogel concentrations forming nonergodic systems.