Summary: Novel Method of Biocompatible Colloidal Stabilization
Encapsulating a dispersion of colloidal particles within a bilayer membrane can
lead to enhanced stability of the dispersion against flocculation, while simultaneously
providing biocompatibility. Many useful colloidal dispersions, such as the titanium
dioxide colloids used in many sunscreens, are very unstable in biological environments.
At low electrolyte concentrations, the 10 50 nm colloidal particles of TiO2 are dispersed
due to electrostatic interactions between the particles. These long range interactions keep
the particles from aggregating. However, at physiological salt concentrations, these long
range interactions are screened, and the particles rapidly aggregate and precipitate from
solution. This phenomena is general to many colloidal particle dispersions essentially
all electrostatically stabilized colloidal dispersions are unstable in a biological
environment. For some particles, additional stabilization can be achieved by adding a
polymer "brush" to the surface of the particles to impart some steric stabilization.
However, this is difficult to do, and does not necessarily impart biocompatibility.
As shown in the figure below, it is possible to wrap up small quantities of
colloidal particles within a continuous bilayer membrane. By controlling lipid phase
behavior, it is possible to reversibly open and close bilayer vesicles to entrap colloidal
particles, macromolecules and even other bilayer vesicles. Once the particles are
entrapped, the aggregation of the particles leading to flocculation is inhibited by the
bilayer membrane. The membrane can also be used to control the chemical environment