Biomedical Engineering Reference
In-Depth Information
(A)
(B)
25
μ
m
Figure 3.4
Recent achievements in stem-cell engineering using nanoscale-based approaches.
(A) Myoblast differentiation on electrospun fibers of polycaprolactone and polyaniline of varying
diameters (ranging from 0.25 to 2 μm). Differentiation and morphology were found to be highly
dependent on the alignment of the fibers [63]. (B) Neuronal differentiation on PDMS scaffolds,
including flat and nanopillar topographies. Higher pillar heights (400 nm) increased and accelerated
neuronal differentiation. Immunostaining for Tuj1, Nestin and Hoescht on 50, 120, 220, and 400 nm
nanopillars (left to right, top to bottom) [36].
(See insert for color representation of the figure.)
mediated by tensile stresses on the cytoskeleton [38]. In addition to purely morphological
effects on cells, stiffness can also impact other cell behaviors. Studies have shown that
stiffness influences migration [39], apoptosis [40], morphology [41], and proliferation [42].
Stem-cell differentiation is another cell behavior that is also highly affected by the
stiffness of the ECM. Pek
et al.
were able to differentiate MSCs into neural, myogenic,
or osteogenic phenotypes depending on whether they were cultured on a low (0.1-1 kPa),
intermediate (8-17 kPa), or high (34 kPa) elastic modulus substrate [43]. Kshitiz
et al.
were able to demonstrate that multipotent cells derived from native cardiac tissue had
enhanced proliferation and endothelial differentiation when cultured on substrates
that more nearly resembled the native myocardial rigidity [44]. Park
et al.
found that
MSCs on softer adhesion substrates had less spreading, fewer stress fibers, lower rates
of proliferation, and higher levels of chondrogenic expression marker collagen-II and
adipogenic marker lipoprotein lipase, while MSCs cultured on stiffer substrates had
more spreading, more stress fibers, higher rates of proliferation, and higher levels of
smooth-muscle cell markers α-actin and calponin-1 [45]. Leipzig and Shoichet found
that neural differentiation is favored on methacrylamide chitosan substrates with
Young's elastic moduli less than 1 kPa and oligodendrocyte differentiation was favored
on stiffer substrates (7 kPa) [46]. Evans
et al.
found that embryonic stem cells cultured
on softer polydimethylsiloxane substrates had upregulated levels of genes implicated in
gastrulation and early mesoderm differentiation, while stiffer substrates induced
osteogenic differentiation [47]. Rowlands
et al.
found that increasing the stiffness (from
9 to 80 kPa) of polyacrylamide gels with adhered collagen, laminin, or fibronectin
ligands increased myogenic differentiation, while osteogenic differentiation occurred
only on the stiffest substrates tested [48]. Thus, differentiation seems to be stiffness
dependent for a number of different stem cells and lineages, although stiffness may not
be the only important factor.
