Biomedical Engineering Reference
In-Depth Information
for each copolymer prepared. With a PBCL block length of 2 kDa,
the CMC was 8 × 10
-8
M, whereas a typical PEO-PCL diblock with
a PCL block length of 5 kDa has a CMC twice that. Conversely, the
addition of a carboxylic acid functional group to a slightly smaller
PCL block (1.8 kDa) increased the CMC of the PEO-PCL diblock by
two orders of magnitude. It should be noted that the addition of the
benzyl carboxylate function group increased the micelle size to 60
nm over the typical PEO-PCL (5 kDa) diblock (40 nm).
(a) (b)
Figure 3.5
(a) α-benzyl carboxylate ε-caprolactone and (b) α-carboxylate
ε-caprolactone monomers. From reference [68].
The ability to tune the CMC by adjusting the functional groups
on the core implies that the thermodynamic affinity of a drug for the
core should change as well. Compared with PEO-PCL (24 kDa PCL
block), a PEO-PBCL micelle with one-fifth of the PCL block length
increased the encapsulation efficiency of cucurbitacin B almost
30%. However, the cumulative release from the PBCL core was
slightly faster than the 24 kDa PCL core. Nonetheless, the increases
in stability and encapsulation efficiency for some drugs are superior
to typical diblock PEO-PCL copolymers.
3.3
Characterization of Cellular Uptake and Pre-
Clinical Efficacy
in vivo
As a first step in understanding what happens to these micelles
in
vivo
, the micelle-cell interaction was studied extensively
in vitro
in
multiple cell lines. It is well known that when PEO chains reside
at the corona, they impart negative zeta potentials on the micelles
[72-74]. A smaller PEO chain would increase the magnitude of this
negative zeta potential because the layer of bound water is smaller
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