Biomedical Engineering Reference
In-Depth Information
especially in retinal epithelium engineering
58
and bioartificial kid-
neydevices.
59
,
60
Thesubstratacanbetissueculturesurfacesorpoly-
meric membranes, generally coated/conjugated with ECM proteins
orcelladhesionmolecules.Thestructuresandcompositionsofthese
bioadhesivemoleculesarecriticalforcellstoreestablish
invivo
-like
cell-cellandcell-matrixinteractionstomaintaincellpolarityanddif-
ferentiated functions.
Primary hepatocytes are one major cell type in cell-based thera-
pies in hepatic tissue engineering and drug metabolism and toxicity
studies.Howtomaintaintheirphenotypicstability
invitro
afteriso-
lation has been a subject of intensive studies. The spatial geometry
of the ECM in hepatocyte culture proves to be important.
29
While
single-layer cultured hepatocytes on type I collagen typically lose
differentiated functions within the first week of culture, the overlay
withasecondlayerofcollagencanrestorethepolarityandfunction.
Hepatocytes cultured in a sandwich configuration adopt
in vivo
-
likemorphologyandintracellularorganizationwithafunctionalbile
canaliculi network. Their characteristic liver-specific functions can
beretaineduptoseveralmonths.
61
Acollagenoverlaycanalsocause
the reorganization of other types of epithelial cells such as MDCK
and normal murine mammary gland with the formation of lumen,
62
highlighting the importance of spatial and temporal presentation of
polarity cues on epithelial cell culture.
Hepatocytes cultured on soft and/or weakly adhesive sub-
strata self-assemble into closely associated multicellular spheroids
that possess structural polarity and functional bile canalicular
channels delimited by tight junctions.
63
The channels are highly
interconnected, mimicking the 3D nature of bile canaliculi in
native liver tissue. Examples of these substrata include agarose,
poly(hyroxyethyl methacrylate), Matrigel, positively charged sur-
face and liver-derived proteoglycan-coated/galactosylated surfaces,
etc.
64
Compared with the 2D monolayer, hepatocyte spheroids
maintain up-regulated liver-specific functions for a long term, in
terms of albumin production, urea synthesis, and cytochrome P450
and glucuronidation activity. Both sandwich-cultured and spheroid-
cultured hepatocytes have been used intensively in bioartificial
liver-assisteddevices(BLAD)and
invitro
studiesofdrugtoxicityand
metabolism.
61
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