Immobilization of discrete cell clusters
within a partially crosslinked matrix prevents
reaggregation of primary tissues and may
provide a means for long-term maintenance of
encapsulated cells. Dissociated bovine adrenal
chromaffin (BAC) cells were suspended
throughout crosslinked polyanionic microspheres
previously shown to be selectively
permeable. Microcapsules approximately 500
µm in diameter were seeded with: 1) three
different densities of BAC cells; and 2) BAC
cells suspended in Matrigel®
or coseeded with a
genetically modified nerve growth factor (NGF)-
releasing fibroblast cell line. Each group was
analyzed in vitro at 1, 4 and 8 weeks for
spontaneous and potassium-evoked release of
catecholamines, and maintained in vitro for up
to 12 weeks for morphological observations.
Over time, release of norepinephrine (NE) and
epinephrine (EPI) diminished, while dopamine
(DA) remained constant from the monoseeded
capsules. In the coseeded group, an increase in
potassium-evoked release of DA was observed
from 1 to 4 weeks, and remained at that level up
to 8 weeks. Encapsulated chromaffin cells
retained a rounded morphology typical of
undifferentiated cells. Intact chromaffin cells
with well preserved and abundant secretory granules were observed ultrastructurally after 4
weeks in vitro. Small neurites from the chromaffin
cells in the coseeded group were observed at 4
weeks with light microscopy, and up to 12 weeks
with electron microscopy. Under static incubation
conditions, 1 mM D-amphetamine resulted
in a significant increase in the output of NE and
DA from the coseeded capsules 8 weeks postimplantation,
as compared to microcapsules
loaded with chromaffin cells alone. Encapsulation
within an immobilization matrix allows
manipulation of the internal environment,
thereby providing the ability to pre-treat cells
with various factors in a non-invasive manner,
which may enhance long-term cellular viability.
