Biomedical Engineering Reference
In-Depth Information
to 30% to 50% of their initial volumes at four to six weeks.
4
,
5
In
contrast,theuseofmacroporousPLGAmicrospheresresultedinthe
maintenance of newly formed tissue volume at 71% of the original
implant volumeat six weeks.
Another advantage of a macroporous PLGA microsphere over a
nonporous PLGA microsphere is a less acidic environment within
degradingPLGAimplants.Theacidicenvironmentwithindegrading
PLGA implants could negatively affect the viability of transplanted
or host cells near and within the implant
in vivo
.
11
Since macro-
porous PLGA microspheres have large void volumes within them,
the PLGA mass of macroporous PLGA microspheres would be much
smaller than that of nonporous PLGA microspheres. The bulk den-
sity of macroporous PLGA microspheres is only ca. 2% of that of
macroporousPLGAmicrospheres.Inaddition,thehighlyporousand
interconnected pore structure of macroporous PLGA microspheres
permitsdiffusionofdegradedPLGAproductsthroughoutthedevice
after implantation, resulting in a less acidic environment than with
nonporous PLGA microspheres.
18.5 Concluding Remarks
Macroporous PLGA microspheres are suitable as both a cell
culture substrate and a cell transplantation vehicle. After high-
density cell expansion on macroporous PLGA microspheres, the
cell-microsphere constructs can be transplanted for therapeutic
applications. This process provide advantages over current meth-
ods,inwhichcellsareculturedon2Dcultureplates,harvestedusing
trypsinization, and transplanted with or without a cell transplanta-
tionvehicle.
Ex vivo
cellexpansionusingmacroporousmicrospheres
in a 3D stirred suspension bioreactor has advantages for clinical-
scale production of transplantable cells over cell expansion using
conventional, 2D culture plates, which have a limited surface area
for cell growth. The use of macroporous PLGA microspheres as
a cell transplantation vehicle, following cell culture, avoids the
trypsinization that is necessary for the harvest of expanded cells
for transplantation and that may cause reduced cell viability and
high apoptotic activity and limit the therapeutic e
cacy of the
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