Self-Assembled Liquid Particles: How to Modulate their Internal Structure - Food Colloids: Self-Assembly and Material Science - page 70

dispersibility of such phases is more complicated. In the pioneering work of
Larsson and co-workers, 5-7 it was established that monoglycerides (e.g., glyc-
erol monooleate) can be dispersed in water using a dispersing agent such as a
block copolymer, whereby sub-micrometre-sized particles with preserved in-
ternal self-assembly structures are formed. In analogy with liposomes, these
dispersed particles were termed cubosomes when their internal structure consists
of a cubic phase and hexosomes when it is a hexagonal phase (achieved by
addition of a third component). These systems are important as membrane
mimetic matrices, 8 as vehicles for the solubilization of active ingredients (e.g.,
vitamins and enzymes), 8,9 and as unique microenvironments for the controlled
release of additives (e.g., drug delivery), 10,11 considering the hypothesis that the
structural arrangement within the particle significantly determines the delivery
properties.
An overview of such systems is provided in this article for monolinolein-
based particles. Recently, we reported 12 that the internal structure of these
particles is not only self-assembled but is also at equilibrium. The internal
structure is in most cases a liquid-crystalline phase of either a cubic or
hexagonal structure, but isotropic fluid structures can also exist at higher
temperatures. 12 Moreover, we proved the reversible exchange of water from
inside to outside the confined internal particle structures during the cooling and
heating cycles. This can easily be modulated by either varying the temperature
or solubilizing oil. The addition of oil at a constant temperature, or the
increasing of temperature at a constant oil content, induces a transforma-
tion from cubosomes to hexosomes and dispersed water-in-oil (W/O)

microemulsions.
We consider also the effect of variation of the lipid composition on the
confined internal structures of the particles. The addition of oil can indeed
lead to new systems: the emulsified microemulsions (EMEs). These are in a
certain sense similar to double emulsions, i.e., they are water-in-oil-in-water
systems. However, they are extremely stable over time. This is caused by the
fact that the dispersed phase is a W/O microemulsion that is dispersed in
water using a high molecular weight hydrophilic secondary emulsifier. 13 We
present evidence that particles having an internal structure of Fd3m (reverse
discontinuous micellar cubic phase (MCP)) can also be created on addition of
oil. Upon adding the oil, the interface is tuned to be more negative, i.e.,
curved towards the aqueous phase. Nevertheless, this curvature effect can be
tuned back by the addition of diglycerol monooleate (DGMO) 14 or other
amphiphilic molecules, which then balances the structural effect of the
added oils.
Small angle X-ray scattering (SAXS) and cryogenic transmission electron
microscopy (Cryo-TEM) were used to analyse the internal structure of the
particles. The results presented here mainly use n-tetradecane (TC) as the oil
phase. All of the following internal structures are currently available for food-
grade applications: cubic bicontinuous, hexagonal, discontinuous micellar
cubic (all liquid-crystalline), and fluid isotropic (microemulsion). 15