Biomedical Engineering Reference
In-Depth Information
sion of zyxin protein, a marker for mature focal adhesions, was decreased on 350-nm-grating
PDMS, leading to smaller and more dynamic focal adhesions. Furthermore, the expression
of integrin subunits α
2
, α
6
, α
V
, β
2
, β
3
, and β
4
were also decreased on the nanograting surface
compared with flat controls [63]. These results suggest that the traction force at focal adhe-
sions on the nanogratings is decreased.
Lee
et al
. also demonstrated direct differentiation of human ESCs into selective neurons on
a nanogrooved poly(urethane acrylate) surface (350-nm-wide ridges/grooves of 500 nm depth)
without any specific induction reagent [64]. The human ESCs on the nanogrooved surface
expressed increased NeuroD1 (a neuronal marker) and decreased GATA6 (endoderm marker)
and DCN (mesoderm markers) compared with controls. Tuj1 (immature neuronal marker),
HuC/D (human neuronal protein) and MAP2 (mature neuronal marker) with well-structured
neurite extension was immunostained positively, while the brachyury (mesoderm markers),
Pdx1 (endoderm marker) and GFAP (intermediate filament proteins of mature astrocytes)
was not found. The results indicate that on the nanogrooved surface human ESCs differentiate
toward neuronal lineages, but not a glial lineage such as astrocytes.
Watari
et al
. showed that nanogrooved surfaces (400 nm pitch of 300 nm depth) enhanced
osteogenesis of human MSCs with respect to the expression of RUNX2 (runt-related tran-
scription factor 2) and osteocalcin, and calcium deposition relative to cells cultured on 1400
or 4000 nm pitch or planar control [65]. Several biosignals, including Wnt and bone mor-
phogenetic proteins (BMPs) signalling pathways, were identified as pivotal regulators in
osteogenic differentiation. Watari
et al.
demonstrated that nanogroove cues enhance
osteogenesis of human MSCs, likely via the BMP signalling pathway, since ID1 (a target of
the BMP pathway) was enhanced on the 400-nm-pitch nanogrooved surfaces in the presence
of osteogenic induction components, while TCF3 and AXIN2 (downstream genes of the
Wnt pathway) were not significantly affected [65].
Responses of Stem Cells to Nanofibrous Structures
Cell anisotropic spreading along fibrous substrates (contact guidance) was reported as early as
in 1952 [68]. Recently, the investigation of cell responses to nanofibrous structure has been
increased due to a wide application of the electrospinning technique. The structure of electro-
spun fibers and its fibrous membrane mimic the native collagen fibrils and native ECM topog-
raphy (Figure 11.1D). The diameters of nanofibers can be modulated ranging from hundreds
of nanometers to a few microns by controlling the electrospinning conditions, such as polymer
type and concentration, solvent type, flow rate, and applied voltage [69]. Some researchers
think that electrospun fibrous meshes display a three-dimensional topographic architecture
since cells might migrate in the space between fibers. However, electrospun fibrous meshes are
usually too compact for cells to penetrate. Furthermore, aligned nanofibers can be obtained
using special collectors such as a rotating collector [70]. Aligned nanofibrous mesh is especially
of interest in applications to study the differentiation of MSCs into differentiated lineages,
such as neuron [69, 71], tendon [72, 73], ligament [74], and cardiac muscle/muscle (Table 11.3)
[75]. In this section, the effect of nanofibrous mesh on stem cell responses is discussed.
Aligned electrospun fiber is reported to promote the neurodifferentiation of stem cells.
Lim
et al
. reported that aligned poly(caprolactone) (PCL) nanofibrous meshes (mean
diameter 480 nm) enhanced the differentiation of rat neural stem cells in the presence of ret-
inoic acid compared with random fibrous meshes or flat films [69]. Similarly, Wang
et al
.
showed that neuronal differentiation (β-III-tubulin) and neurite outgrowth of human ESCs-
derived neural precursors were promoted on aligned silk fibroin nanofibrous meshes (mean
fiber diameter 400 nm) compared with the random nanofibrous meshes and flat controls [76].
