Biomedical Engineering Reference
In-Depth Information
This has also been demonstrated on pAl in an extensive review recently
published by Br¨ggemann.
141
As an example, Popat et al.
140
found that pAl
surfaces with a pore size of
72 nm enhance the spreading and proliferation
of MSCs over 1 day and 7 days, respectively. Additionally, higher alkaline
phosphatase activity as well as increased levels of calcium and phosphorous
were observed compared to flat Al surfaces. Human osteoblast cells were also
shown to attach, spread and proliferate at a higher rate on pAl surfaces (pore
size
B
d
n
3
r
4
n
g
|
7
160 nm) than on control samples.
142,143
Furthermore, filipodia were
found to readily attach to the pAl surface. Additionally, Swan et al.
139
dem-
onstrated that the attachment and spreading of osteoblast cells could be
enhanced by the adsorption of vitronectin or immobilisation of an RGD
peptide on pAl substrates.
Whilst there has been increased demand for the use of pAl to investigate
the influence of topographic features on cell attachment, there has only been
two reports of pAl gradients to investigate cellular response. The attachment
of SK-N-SH neuroblastoma cells on pAl gradients was investigated by Kant
et al.
47
Interestingly, the highest cell attachment was observed for the col-
lapsed pore brush-like region of the gradient, with many interconnecting
networks. At smaller pore sizes, the cells displayed a more neuronal
phenotype, with long bipolar extensions. Wang et al.
138
demonstrated that
human MSC attachment and cell density decreased with increasing pore
size. Additionally, after 2 weeks, osteogenesis of hMSCs was found to be
optimal at a pore size of 120-230 nm and a 10 nm pore width. Given the
increased stability of pAl over pSi, it is envisaged that the use of pAl gradients
will become increasingly popular for longer-term cell culture experiments
with the purpose of investigating the effect of porous materials on cell
differentiation.
B
.
10.2.1.3 Surface Roughness Gradients
Methods that have been developed to generate roughness or other topo-
graphical gradients in addition to those described previously include
nanoparticle gradients based on an underlying chemical gradient
51,112,144,145
or electrostatic interactions,
146,147
annealing of polymer surfaces via a tem-
perature gradient,
148-150
photolithography to create grooved surfaces
151
and
sandblasting coupled with subsequent chemical polishing.
25,111
Several
studies have demonstrated the influence of surface roughness on cellular
response.
25,52,103
The obvious advantage of using gradient surfaces for such
experiments is that a wide range of surface roughness values can be in-
vestigated simultaneously under identical experimental conditions.
One approach for generating topography gradients is to use a chemical
gradient such as plasma polymer,
51
silane,
112,145
or brush co-poly-
mer
112,144,152
gradients as a template to adhere nanoparticles to a surface in
a gradient fashion. This method may be advantageous as the size of the
topographical features can be controlled by selecting the size of the nano-
particles. Plasma polymer gradients were used by Goreham et al.
51
to
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