Biomedical Engineering Reference
In-Depth Information
50
40
30
25
20
15
10
5 nm
FIGURE 2.9
TEM and agarose gel electrophoresis of water soluble IOMNPs at 5-50 nm.
Courtesy of Ocean NanoTech. (For color version of this figure, the reader is referred to the online
version of this topic)
even proteins and peptides. Synthesis of a few of these NMs will be discussed
below.
2.3.1 Liposomes
The original models of nanoscaled drug delivery devices are the liposomes
that were discovered in mid-1960s.
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These are spherical NMs made of lipid
bilayer membranes that have an aqueous interior but can be unilamellar (having
a single lamella of membrane) or multilamellar (having multiple membranes).
These are used as effective drug delivery systems for cancer chemotherapeutic
drugs and other drugs. Potent and toxic drugs like amphotericin and hamycin
when formulated as liposomal drugs exhibit improved efficacy and safety com-
pared with conventional preparations. In these liposomes, water-soluble drugs
are loaded in an aqueous compartment and lipid soluble drugs are incorporated
in the liposomal membrane 2. However, the rapid degradation of liposome and
clearance by the liver macrophages
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reduces the duration of action of the drug
it carries. This can be circumvented with the advent of stealth liposomes that are
coated with materials like polyoxyethylene,
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which prevents opsonization of
the liposome and uptake by macrophages.
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Other ways of prolonging the cir-
culation time of liposomes are incorporation of substances like cholesterol,
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PVP polyacrylamide lipids,
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and high transition temperature phospholipids
distearoyl phosphatidylcholine.
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Phospholipid vesicles called liposomes have been recognized in biology and
medicine, as promising nanoscaled drug delivery devices.
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Liposome prep-
arations can lead to multilamellar vesicles (MLV) or the development of the
sonicated unilamellar vesicles (SUV).
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Both preparations show relatively low
volume of entrapped aqueous space per mole of lipid restricting the ability to
encapsulate large macromolecules. This can be a result of the MLV having most
