Biomedical Engineering Reference
In-Depth Information
Amphiphilic polyaspartamides grafted by C18, MPEG, and API were also
prepared by us, which formed spherical nano-aggregates of 88 nm in phosphate
buffered saline (PBS, Ph 7.4) and their SEM picture is shown in Figure 8.
Conjugation of C18 chains reinforced the hydrophobic interaction between the
long alkyl chains, and thus small size of aggregates below 100 nm could be
formed by self-assembly.
5. Phase Transition Behaviors
The phase transition behavior of polyaspartamides centers around ionic or
hydrophobic groups and their DS in the polymer chain. The pH of the phase
transition is controlled by the pK
a
and DS of the ionic groups grafted to the
polymers. When the hydrophobic and hydrophilic balance is well defined,
polyaspartamides could present lower critical solution temperatures (LCST) due
to hydrogen bonding between amide groups in the polymer backbone and water
molecules.
Novel polyaspartamides grafted with 1-(3-aminopropyl)imidazole, whose
pK
a
was 6.5, were prepared for drug delivery application by our research group.
[27] As shown in Figure 9, they showed sharp pH-responsive phase transition
100
80
60
DS of API
0%
42%
51%
76%
88%
95%
40
20
0
4.5
5.0
5.5
6.0
6.5
7.0
7.5
8.0
8.5
9.0
pH
Fig. 9. Light transmittance of API-g-polyasparagine as a function of pH.
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