Stem Cell Differentiation Depending on Different Surfaces - Tissue Engineering: Cell-Surface Interactions for Tissue Culture - page 271

a rough topography [ 49 ]. According to their origin, osteoblasts prefer rougher
surfaces, whereas fibroblasts favor smooth surfaces. In bone tissue engineering, it
has been shown that an increased surface roughness enhances osteogenic differ-
entiation [ 18 , 50 , 51 ]. However, the results are conflicting. Some publications
report no change in response to rough surfaces [ 52 ] or even a reduction in cellular
response [ 53 ]. One significant problem might be the low reproducibility of
roughness. Even though two surfaces exhibit the same roughness, their topography
can appear very different. Furthermore, intrabatch and interbatch variations of
biomaterials may cause difficulties. Other reports suggest the spacing between
ligated integrins, which are essential for adhesion and signal transmission, to be
less than 70 nm. Thus, larger nanoscale spacing fails to trigger differentiation
signals [ 54 - 56 ].
However, the behavior and functionality of cells may be influenced by different
topographic sizes, ranging from macroscale to microscale and nanoscale features
[ 57 ]. The smallest feature size shown to affect cell behavior is 10 nm [ 58 ]. A
sizable number of publications have described the positive influence of nanoscale
patterns on the differentiation of MSC. Osteogenic differentiation, for example, has
been observed on nanopattern surfaces of 17-25 nm [ 59 ], 50 nm [ 60 ], and 100 nm
[ 61 , 62 ]. Myogenic differentiation has been demonstrated by cultivating bovine
aortic endothelial cells on nanotubes of 1 lm length and 30 nm average pore
diameter [ 63 ]. Even differentiation of hMSC into the neuronal lineage has been
monitored by using nanogratings of 350 nm as a culture substrate [ 64 ].
In several studies, cells grown on microscale rough surfaces demonstrated a lower
proliferation rate compared with those grown on smooth surfaces. Furthermore, it
was found that cells could not cross over large grooves, glens, holes, and craters [ 18 ].
Cells formed a confluent layer within these irregular surface areas much faster than in
regions of even surfaces owing to the limited space. Consequently, cells in grooves,
glens, holes, and craters showed the pileup phenomenon, which results in bone
nodule formation and finally in osteogenic differentiation. Thus, cells grown on
surfaces with high roughness displayed a higher alkaline phosphatase activity and
bone morphogenic protein production, which supports osteogenic differentiation.
Graziano et al. also proved this effect by cultivating hMSC on convex and concave
surfaces [ 139 ]. Cells cultured on concave surfaces showed better cell-matrix inter-
actions, and after 30 days of cultivation, the production of specific bone proteins,
such as osteonectin and bone sialoprotein, was demonstrated.
Similar effects have been observed in our research group by cultivating adMSC
and ucMSC for 35 days on a macroporous, interconnected zirconium dioxide
(ZrO 2 ) biomaterial (Sponceram, Zellwerk) with an average pore size of 600 lm.
Scanning electron microscopy images illustrated a confluent cell layer in the
cavities of the matrix (Fig. 2 ). Within these areas an increased bone nodule for-
mation was observed. Moreover, the presence of specific bone proteins such as
collagen 1, osteopontin, and bone morphogenic protein was verified using poly-
merase chain reaction analysis.
The influence of microscale surface topography on adipogenic differentiation
has also been observed [ 65 ]. The results indicated an advanced adipogenic