Alginate Release 57
It should be noted that this is a very convenient procedure for immobilizing
growth factors. The procedure is carried out at room temperature using gentle,
buffered solutions. Thus care should also be taken to see that the CaCl
2
is not ice cold.
2. Variations in microbead shape: In our initial experience with the alginate release
system, we utilized the microbead shape. However, when we started using the
system in vivo, we found that the beads were sometimes a bit too cumbersome to
use in certain situations, as they often would migrate with gravity or easily dis-
lodge with even the slightest tissue manipulation. Therefore, we started construct-
ing other shapes out of the identical alginate material. We have made more
practical delivery-system shapes, including a filamentous (string-shaped) and a
flat-sheet shaped design. We have found that both shapes can be more functional
in vivo in some anatomic regions. The filamentous configuration is advantageous
because it can be wrapped around certain structures, while the flat-sheet system
can be laid securely adjacent to appropriate tissues to target release.
To make the alginate filament system, the mixture of 3% alginate and growth
factor is extruded through a 25-gauge needle into the 1.5% calcium chloride
solution. To ensure uniform diameter of the string, a syringe pump apparatus is
utilized to apply uniform pressure to the syringe. To make the flat sheet alginate
system, our engineering department constructed a special device made of Lucite
that fits securely onto a syringe and extrudes a uniformly flat alginate sheet
through a slit at its endpoint. The slide dimensions are 25 mm × 0.25 mm. Again,
a mixture of 3% alginate and growth factor is extruded through this device into
the 1.5% CaCl
2
solution. To facilitate string and sheet formation, we found it
advantageous to submerge the device tip in CaCl
2
solution during construction.
References
1. Ko, C. Y., Dixit, V., Shaw, W., and Gitnick, G. (1995) In vitro slow release pro-
file of endothelial cell growth factor immobilised within calcium alginate
microbeads. Art Cells, Blood Subs. and Immob. Biotech. 23, 143–151.
2. Dixit, V., Darvasi, R., Arthur, M., Brezina, M., Lewin, K., and Gitnick, G. (1990)
Restoration of liver function in Gunn rats without immunosuppression using trans-
planted micro-encapsulated hepatocytes. Hepatology 12, 1342–1349.
3. Ko, C. Y., Dixit, V., Shaw, W., and Gitnick, G. (1997) Extensive in vivo angio-
genesis from the controlled release of endothelial cell growth factor: implications
for cell transplantation and wound healing. J. Controlled Rel. 44, 209–214.
4. Ko, C. Y., Dixit, V., Shaw, W., and Gitnick, G. (1995) Succesful xenotrans-
plantation of microencapsulated hepatocytes in the rat fasciovascular groin flap.
Presented at the Tenth World Congress of the International Society for Artificial
Organs, Taipei, Taiwan. Abstract book: 42.
5. Borud, L. J., Shaw, W., Passaro, Jr. E., Brunicardi, F. C., and Mullen, Y. (1994)
The fasciovascular flap: a new vehicle for islet transplantation. Cell Transplant.
3, 509–514.