Biomedical Engineering Reference
In-Depth Information
small volume of blood and it restrains direct transplantation of HSPCs to patients. Surface-
aminated polyethersulfone nanofibers have been demonstrated to be one approach to
expand HSPCs. Scanning electron microscopy images revealed that cell colonies were
formed on nanofibers [50] and the chain length of the grafted amines have an impact on the
proliferation rate of HPSCs [51].
Natural Polymers
Natural polymers contain essential components of natural ECM and they have been fabri-
cated into nanofibers for culturing stem cells. For example, collagen is found in abundance
in natural ECMs. Type I collagen nanofibers by electrospining technology have been
prepared for examining the morphology, growth, adhesion, cell motility, and osteogenic
differentiation of human bone-marrow-derived MSCs. The MSCs grown on 500-1000 nm
nanofibers showed significantly higher cell viability than on a two-dimensional surface [52].
Silk is another popular natural polymer to synthesize nanofibers. Silk nanofibrous mats
with fibroin diameter 700 ± 50 nm were found to support extensive MSC proliferation and
matrix coverage [53, 54].
Copolymers/Blends
Great efforts have been made to modify polymeric nanofibers using copolymer electrospinning
or blending with other polymeric materials in order to improve processability of polymers for
nanofiber manufacturing, in order to resemble the natural ECM as much as possible, and to
promote stem-cell interactions with matrices.
Aligned poly(
l
-lactic-co-ε-caprolactone) [P(LLA-CL)] co-polymer nanofibers were electros-
pun for growth of human coronary artery smooth muscle cells (SMCs). Cell adhesion to the
copolymer nanofibers was quite similar to a two-dimensional surface, while SMCs' proliferation
rate on nanofibrous matrices was twice as fast as on a two-dimensional surface in 7 days [55].
Poly(ethylene oxide terephthalate)-poly(butylene terephthalate) (PEOT/PBT) nanofibers were
also explored for culturing stem cells due to their adjustable surface energies [56]. Higher surface
energy (hydrophilic) material leads to a higher cell attachment with a spindle-like shape
whereas lower surface energy (hydrophobic) material results in lower cell attachment and a
rounded morphology [57, 58]. Recently, Moroni
et al
. found that nanoporous PEOT/PBT
microfibers promoted MSC spread, attachment, and proliferation, while smooth microfi-
bers without nanopores led to rounded aggregated cells [59].
Blending nanofibers with different polymer supports can form a three-dimensional network
and help cell migration. An aligned nanofibrous mesh essentially behaves as a two-dimensional
sheet on which cells can only migrate along the surface, rather than a three-dimensional matrix
in which cells are capable of infiltrating. To overcome this problem, a novel three-dimensional
unwoven macroporous nanofibrous (MNF) matrix was manufactured from PLLA and PCL
(w/w 9:1) using an electrospinning-based yarn assembly technique. Human MSCs derived
from ESCs were seeded onto the MNF matrix and a much higher cell proliferation were
observed [60].
Blending with natural polymers is another attractive strategy to mimic natural ECM.
Stem-cell responses to the blending matrices have been studied extensively through hybrid
nano- and microfibrous matrices produced by blending starch and PCL (30/70 wt%).
Microfibers were impregnated, as much as possible, with electrospun nanofibers. Bone-
marrow MSCs growing on the hybrid matrices presented a different morphology, being
able to bridge between microfibers. Cells along the nanofibers showed a much-stretched
morphology. When cells stretch themselves, the receptors are also stretched and activated,
