Application of alginate gel as a vehicle for liposomes. II. Erosion of alginate gel beads and the release of loaded liposomes.
The possibility of producing calcium-induced alginate gel beads as a vehicle for liposomes was explored. The maximal loading of egg phosphatidylcholine liposomes (ca. 26 nm in diameter) in a fully-cured bead (1.2 mm in radius, initial alginate concn. of 4%) was 2.9 x 10(-6) mol/bead or ca. 18%, and the size of the bead slightly increased with an increase in liposome loading. The liposomes were well maintained within both fully-cured and washed beads. The liposome release from the fully-cured bead was much slower than that from the corresponding washed bead in a pH 7.4 releasing medium. The greater the liposome loading, the faster the release of the vesicles. The liposome release was investigated in terms of liposome loading, swelling of the gel body, calcium discharge and gel erosion, using washed beads. The liposome loading did not affect the bead erosion or calcium discharge but did the initial swelling ratio and liposome release. The results suggest that the loaded liposomes are not uniformly distributed in the bead but are rather gradually concentrated to the center. Such an inhomogeneous distribution of liposomes is possibly due to the fact that the gelation occurred instantly on the surface of the droplets, and the resulting gel network or layer acts as semipermeable membrane for liposomes and forces the vesicles to move into deeper concentric sections as gelation proceeds to the interior. As the liposomes loading increases, the forced migration might be very limited because of concentrically decreasing extra room to accommodate the vesicles in the bead.
Takagi
I
I
Faculty of Pharmaceutical Sciences, Nagoya City University, Japan.
Nakashima
H
H
Takagi
M
M
Yotsuyanagi
T
T
Ikeda
K
K
D000464:Alginates; D002118:Calcium / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D008081:Liposomes; D008863:Microspheres; D011108:Polymers / Q000378:metabolism
D000464:Alginates; D008081:Liposomes; D011108:Polymers; D002118:Calcium