Biomedical Engineering Reference
In-Depth Information
Fig. 5
Formation of PMPC-
b
-PDPA block copolymer vesicles. (Reproduced from ref.
Du et al.
2005
)
Fig. 6
Sequence of microscopy images showing the dissolution of a giant polymersome of P2VP-
b
-PEO upon addition of dilute acetic acid. (Reproduced from ref. Borchert et al.
2006
)
sensitive polymersomes for efficient DNA encapsulation (Lomas et al.
2007
)
using pH-sensitive diblock copolymers, poly(2-(methacryloyloxy)ethyl-
phosphorylcholine)-
b
-poly(2-diisopropylamino)ethyl methacrylate) (PMPC-
b
-
PDPA, see Fig.
5
), developed in Armes' group (Du et al.
2005
).
PMPC is a phospholipid-like, biocompatible, and stealthy hydrophilic polymer,
while PDPA is a polybase that has a pH-dependent solubility in water (p
K
a
5.8-6.6).
Such diblock copolymers form stable vesicles at physiological pH but rapidly dis-
sociate at around pH 5-6. DNA was encapsulated within these PMPC-
b
-PDPA
polymersomes at neutral pH, and lowering the solution pH then caused the disrup-
tion of the polymersomes and the formation of DNA-copolymer complexes.
Förster's group has used poly(2-vinylpyridine)-
b
-polyethylene oxide (P2VP-
b
-
PEO) copolymers to produce another example of fast, complete release of polymer-
some contents via pH-induced dissolution (Borchert et al.
2006
). P2VP is also a
polybase that is insoluble in water under neutral and alkaline conditions. However,
when the pH is below 5, P2VP is protonated and becomes water-soluble. Fig.
6
shows the rapid dissolution of a P2VP-
b
-PEO giant polymersome within around
30 sec resulting from the addition of dilute acetic acid.
Du and Armes have reported that variation of pH could be used to tune the
membrane permeability of cross-linked polymer vesicles in THF/water mixtures
(Du and Armes
2005
). These vesicles are formed by a pH-responsive, hydrolyti-
cally self-crosslinkable copolymer, poly(ethylene oxide)-
b
-poly(2-(diethylamino)
ethyl methacrylate-
stat
-3-(trimethoxysilyl)propyl methacrylate) (PEO-
b
-P(DEA-
stat
-TMSPMA)). DEA homopolymer is water soluble at low pH and becomes
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