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For an emulsion, feff is given as:
feff ¼
Vdroplets Vemulsion
(24.8)
where Vdroplets can be simply calculated from the density rLipid and mass mLipid of the lipid as: Vdroplets ¼
mLipid rLipid :
(24.9)
In a liposomal suspension, only a small portion of the lipid VLipid occupies the total volume of a liposome VLiposome: 4 VLiposomes ¼ npr 3 3
(24.10)
mLipid 4 VLipid ¼ pnðr 3 ðr dÞ3 Þ ¼ rLipid 3
(24.11)
Thus, the viscosity of a liposomal system may be much larger than that of an equivalent system with the same amount of lipid dispersed in the form of droplets: h ¼ h0 ð1 þ 2:5feff RÞ
(24.12)
VLiposome 43hpr 3 ¼ mLipid VLipid r
(24.13)
where
R¼
Lipid
III.D.3. Manufacture of liposomes Liposomes may be manufactured using a variety of different manufacturing procedures including thin-film rehydration, freeze-drying rehydration, reverse-phase evaporation, detergent depletion, membrane extrusion, high-pressure homogenization or microfluidization, and ultrasonication by