Biomedical Engineering Reference
In-Depth Information
the composition of DPPC: cholesterol: DSPE-PEG2000: DSPE-PEG2000-folate
at 80: 20: 4.5: 0.5M ratio. Magnetic hyperthermia at 42.5°C and 43.5°C synergisti-
cally increased the cytotoxicity of MagFolDox. The results suggest that an inte-
grated concept of biological and physical drug targeting, triggered drug release
and hyperthermia based on magnetic field influence can be used advantageously
for thermo-chemotherapy of cancers.
It is nearly impossible to incorporate inorganic nanoparticles within the mem-
brane of liposomes because of their very thin membrane thickness (3-5 nm).
However, this becomes possible, even still challenging, with polymersomes due
to the thick membrane (5―30 nm) and toughness resulting from polymer char-
acters. The soft magnetic shells are especially promising for drug delivery,
because their internal compartment is available for encapsulation of water-solu-
ble species and the possible toxicity arising from cells directly contacting the
iron oxide would not be an issue because it is embedded in the copolymer.
Application of a magnetic field could trigger the transient opening of the bilayer
and the release of an encapsulated content. The pioneer work on magnetic poly-
mersomes has been made by Lecommandoux & Sandre et al. (Lecommandoux
et al.
2005
). They have prepared polymersomes of PGA
56
-
b
-PBD
48
loaded with
surfactant-coated g-Fe
2
O
3
nanoparticles in the layer of PBD blocks, and studied
their structural transformation under magnetic field by small angle neutron scat-
tering (SANS). Anisotropic SANS data detected with a 2-dimensional detector
provide experimental evidence of the capability to modify the shape of these
hybrid membranes in response to a magnetic field of an intensity as low as
290 G. Analyses of the anisotropic SANS patterns (at intermediate wave vector
q range) have shown that the portions of membranes mostly affected by the
magnetic field are those with their normal vector parallel to the field. The
membrane becomes stretched in these portions (decrease of the apparent mem-
brane thickness) or almost equivalently the nanoparticles move away from
the magnetic poles.
Our group worked on the LC polymersomes PEG-
b
-PA444 and PEG-
b
-
PAazo444 that contain diamagnetic mesogens (Hocine et al.
2011
). We hoped to
achieve the structural changes triggered by magnetic field using the intrinsic posi-
tive diamagnetic response of the LC polymers. Interestingly, for temperatures
between 65 and 80°C, the application of a magnetic field of 1.4 T can increase the
membrane thickness by up to 50% without significantly changing the inner volume
of vesicles. This structural change is consistent with the alignment of LC domains
under magnetic field. While thickness changes could happen in polymersomes
loaded with magnetic nanoparticles as discussed above, to the best of our knowl-
edge, this is the first time that an increase in membrane thickness has been observed
in a pure polymer vesicle system.
We envision that magnetic field triggered drug release from SIONs-loaded mag-
netic polymersomes would be achieved in the near future provided that the hydro-
phobic block is composed of suitably designed liquid crystalline polymer or
crystalline polymer with proper transition temperature by analogy with the gel-to-
liquid crystalline phase transition in lipid DPPC.
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