Biomedical Engineering Reference
In-Depth Information
Figure 13.3 shows a sample graph of the TLI as a function of pressure. The
CP is determined to be the inflection point of the TLI curve, which
corresponds to a peak in its first derivative. Sample graphs of two typical
cases of SLI curves are shown in Figures 13.4 and 13.5. Figure 13.4 illustrates
an example with no micellization; the SLI increases sharply at the CP, but
remains constant until then. By contrast, Figure 13.5 illustrates an example
with micellization, where upon decreasing pressure, the SLI starts increasing at
the MP, and then increases sharply at the CP.
A complete example of those early feasibility studies by Winoto et al.
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is
shown in Figure 13.6 for 0.5 wt% polystyrene-block-polyisoprene (MW 11.5k-
b-10.5k) in propane. As explored by Tan et al.,
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the CP and MP can be
estimated from statistical associating fluid theory (SAFT1) that captures the
behavior of the corresponding homopolymers. Such mean-field theories
cannot account for detailed micelle structure, but can capture the onset of
micelle formation, for example on the basis of a nanophase separation
hypothesis. While all these results showed in general that that NCM can be
used to form micelles, the results were for model copolymers that are not
directly applicable to drug delivery.
d
n
4
y
3
n
g
|
1
Figure 13.6
Pressure-temperature phase diagram of polystyrene-block-polyisoprene
(11.5k-b-10.5k) in near-critical propane. The concentration of polymer
in solution was 0.5 wt%. Re-plotted on the basis of data taken from
Winoto et al.
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