Biomedical Engineering Reference
In-Depth Information
Pore size gradient
1 µ
m
1 µ
m
1 µ
m
1 µ
m
1 µ
m
1 µ
m
1 µ
m
300 nm
150 nm
300 nm
1
1
1
2
2
2
3
3
3
4
4
µm
4
µm
µm
100 µ
m
100 µ
m
100 µ
m
Figure 11.2
Cell responses on pore-size gradients. Pore-size gradients were created on N-type Si
wafers, so called n-type porous silicon gradients (n-pSi). The n-pSi with average surface pore sizes
ranging from 5 to 230 nm and ridge roughness from 3 to 22 nm were fabricated using an
electrochemical etching approach in a HF-based solution. These new surfaces allow stem cells to
grow at least 1-2 months. Cell morphology of rat bone marrow-derived MSCs (rBMSCs) was
affected on the n-pSi dependent on the pore size and nanoroughness between pores. Cells display a
round shape at the high nanoroughness end but a spread-out shape at the low nanoroughness end of
the gradients. The subsequent osteo- and adipogenic differentiations of rBMSCs were improved by
the surface topographies dependent on the positions and local cell density along the gradients [46].
(See insert for color representation of the figure.)
of the spacing between pores may be different and affect cell responses. Due to the difference
in the fabrication processes, some porous surfaces contain a flat interpore area, while some
contain a rough area. Wang
et al
. showed that a porous Si surface with 200-nm pores with
rough ridges (Ra ~10 nm) stimulated osteogenesis of rat MSCs [46]. Therefore, it might lead to
a wrong conclusion on porous substrates without consideration of the topography of the
interpore area. We believe that not only the averaged pore size, but also pore-to-pore distance,
solid surface fraction, solid surface roughness, and overall surface roughness need to be con-
sidered for evaluating the effect of porous substrates on stem-cell behaviour [47].
In order to systematically investigate the porous effects on cell responses, a substrate with
pore-size gradients is especially required for high-throughput screening in order to reduce the
time and the material required for sample preparation [48]. More importantly, topographic
gradients reduce the difference between discrete samples and individual experiments, and the
cellular activity on different topographies can be compared at the same culture condition. By
adjusting the parameters of the chemical or electrochemical etching process, silicon (Si) or
