Biomedical Engineering Reference
In-Depth Information
produce constructs with varying stiffness for endothelial cell
culture.
107
Matrigel is rich in laminin, collagen IV, and heparan sul-
fate proteoglycans and forms more compliant gels compared with
type I collagen, as does fibrin.
57
However, it is di
cult to isolate and
quantifytheaddedeffectsofotherbiochemicalparametersoncellu-
larbehavior,asECMproteinsareinherenttothesescaffoldsfromthe
outset.
Discounting biochemical factors, an ideal scaffold material
should provide handles for controlling material stiffness, strut size
and length, connectivity, and pore size, thus resulting in the ability
to regulate bulk elasticity and porosity. Even if cells sit on a scaf-
foldwithnanofeatures,cellscanassessthestiffnessofthebasepoly-
mer itself; struts that are on the order of the size of cells essentially
present cells with a 2D instead of a 3D surface; strut length and
connectivity determine pore size, which influences shear stresses,
interstitial flow, and ability to migrate. Previously presented con-
structs by and large cater for this, including established polymers
such as hydrogels and polyglycolide (PGA), polymers under clinical
investigation such as polyorthoester and polyhydroxyalkanoate,
108
and novel biomaterials such as self-assembling peptide chains
RAD16.
109
A few examples where these factors are taken into account are
given here. Hepatocytes cultured in a PEG hydrogel and layered into
a 3D architecture improved hepatocyte survival and liver-specific
function.
72
PGA-urothelial cells composites that were implanted
into mice and retrieved at extended times demonstrated multilay-
ered sheetlike structure formation.
110
RAD16-I has been used for
endothelial sprout formation studies
111
as well as to foster tissue-
like function of hepatocyte progenitor cells.
112
Besides providing an optimal
in vitro
biomechanical microenvi-
ronment for cells, designs geared towards tissue implants should
alsomatchthemechanicalpropertiesofthetissueatsightofimplan-
tation.Forlong-term
invitro
cultureandimplants,scaffolddegrada-
tion properties are also important as part of the tissue-remodeling
process, which results in changes in biomechanical properties
and determines the tissue functionality and implant longevity.
Scaffold integrity should be maintained for as long as it takes cellu-
larconstructstoproduce theirownECMandassemblereplacement
architecture.
108
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