L. Frederiksen et al., PREPARATION OF LIPOSOMES ENCAPSULATING WATER-SOLUBLE COMPOUNDS USING SUPERCRITICAL CARBON-DIOXIDE, Journal of pharmaceutical sciences, 86(8), 1997, pp. 921-928
In this paper the development of a new preparation method of liposomes
containing a water soluble marker (fluorescein isothiocyanate-dextran
(FITC-dextran) or zinc phthalocyanine tetrasulfonic acid (TSZnPc) usi
ng supercritical carbon dioxide (called ''the supercritical liposome m
ethod'') is described. The apparatus used consisted of two main parts:
the high-pressure part, in which the lipid components 1-palmitoyl-2-o
leoylphosphatidylcholine (POPC) and cholesterol (Chol) (7:3 molar rati
o) were dissolved under pressure in supercritical carbon dioxide, and
a low-pressure part, in which the homogeneous supercritical solution i
s expanded and simultaneously mixed with the aqueous phase to yield li
posomes encapsulating the water soluble marker. Addition of 7% absolut
e ethanol to carbon dioxide at 25 MPa and 60 degrees C and the use of
a high-pressure recycling system during 30 min form the homogeneous so
lution with high reproducibility of both lipid components and resulted
in an equal expansion profile (recovery after expansion versus time)
of POPC and Chol, incubation of the lipid components during 60 min at
the above mentioned conditions generated only 3% degradation. The aver
age size of the liposomes was about 200 nm and could not be influenced
by the experimental conditions used. Optimal values for encapsulated
Volume (1.25 L/mol) and efficiency (20%); of the liposomes were obtain
ed using statistical experimental design by using the water soluble ma
rker TSZnPc and an encapsulation capillary with 5.0 cm length and 0.5
mm inner diameter. The total amount of ethanol used to obtain an encap
sulation efficiency of 20% was 15-fold reduced compared to the ethanol
injection method of Batzri and Korn.