Biomedical Engineering Reference
In-Depth Information
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Figure
6.1
Spotted vesicles imaged by z-sectioning confocal microscopy while
aspirated in micropipettes. Cation-induced, lateral phase segregation of
charged PAA-PBD and neutral, fluorescently-labeled PEO-PBD diblock
copolymers formed at pH 4, 0.1 mM calcium at PAA-PBD content of
(a) 25%, (b) 50%, and (c) 75%. (Reproduced from Christian et al.
10
with
permission from Macmillan.)
reduced chemical permeability compared to liposomes. To achieve prolonged
circulation time in vivo, liposomes have to be modified with poly(ethylene
glycol) (PEG), which are then known as ''stealth liposomes''. In contrast, most
polymersomes are intrinsically stealthed in that they are typically made from
amphiphilic copolymers consisting of nonfouling polymers such as PEG,
dextran, and poly(acrylic acid) (PAA).
The presence of large watery interiors and robust hydrophobic walls makes
polymersomes suitable for encapsulation and controlled delivery of both
hydrophilic (e.g. proteins, siRNA, DNA, chelated Gd) and hydrophobic
species (e.g. paclitaxel, doxorubicin , quantum dots). For instance, Li et al.
have reported loading the hydrophobic anticancer drug paclitaxel (PTX) into
PEO-PBD polymersome membranes.
11
The Ji and Qiu groups investigated the
encapsulation of the hydrophilic anticancer drug doxorubicin hydrochloride
(DOX?HCl) into the polymersome lumen.
12,13
Kataoka et al. reported that
myoglobin encapsulated inside polyion complex vesicles could perform
reversible oxygenation/deoxygenation reactions.
14
Palmer et al. reported that
hemoglobin-loaded PEG-poly(e-caprolactone) (PEG-PCL) polymersomes had
similar oxygen affinities to human red blood cells.
15
Hammer et al. showed
that near-infrared (NIR)-emissive polymersomes prepared by stably incorp-
orating large multimeric porphyrin-based NIR fluorophores into the thick
polymersome membrane were able to penetrate through the dense tumor tissue
