Biomedical Engineering Reference
In-Depth Information
including trace amounts of potentially toxic organic solvents left in the micelle,
low drug loading, and burst release of the drug, to name a few.
We recently developed a new technology that can address these problems by
using a near-critical solvent, which is a compressed gas, and simply reducing the
pressure to induce micellization, referred to as the near-critical micellization (NCM)
method. In addition to low viscosity and high diffusivity, which promote mass
transfer, near-critical solvents are easy to remove by spontaneous and complete
evaporation. More importantly, solvent capacity and selectivity can be tuned
precisely with its density via pressure, temperature, or both, which, in contrast to
liquid solvents, allows for high-resolution control of the NCM process.
8,12
d
n
4
y
3
n
g
|
1
13.2 Early Feasibility Studies on Model Systems
The first step in developing the NCM process was to understand its physics on
simple, well-defined model systems, such as polystyrene and polyisoprene.
Towards this end, Winoto et al.
13
used an experimental set-up shown in
Figure 13.1, in which a small high-pressure, variable-volume (y1cm
3
) cell is
used to detect cloud pressure (CP) and micellization pressure (MP) transitions.
It is equipped with a floating piston, so that the pressure can be changed
Figure 13.1
A simplified apparatus schematic diagram. (Reproduced from Winoto
et al.
13
with permission from the American Chemical Society.)
