Biomedical Engineering Reference
In-Depth Information
polymer brushes of poly(acryl amide) (Figure 10.9C).
112,144,152
These brushes
displayed a gradient of chain length and, hence, more nanoparticles were
adsorbed onto the longer chains than the shorter ones. Alternatively, elec-
trostatic interactions can be used (i.e., without using a chemical gradient
template) to create nanoparticle gradients (Figure 10.9B).
146,147
Hot embossing has been employed to generate a grooved surface with a
gradient in terms of the pitch of the grooves.
151
A template was created using
photolithography and etching the pattern into a silicon master. The tem-
plate was then pressed into a PMMA layer under elevated temperatures and
then slowly released whilst the temperature was reduced. In other experi-
ments, a gradient temperature stage had been used to influence film
microstructure, phase transitions, polymer de-wetting and crystallisation
rates across the surface.
148-150
Nanopillar gradients have been prepared by Reynolds et al.
153
in a four-
step process to investigate the attachment and migration of a co-culture of
fibroblast and endothelial cells. Initially, an array of aluminium nanodots
was generated on a quartz slide through electron beam lithography.
154
A thin
plasma polymer thickness gradient of hexane was then deposited over the
nanodot surface.
7
This thickness gradient was then used as a sacrificial
etching layer during reactive ion etching to create a gradient in the height of
nanopillars. Finally, the aluminium layer was removed by wet etching. This
master gradient was then replicated in polystyrene by injection moulding to
create identical replicates for cell culture experiments. Fibroblast and
endothelial cell co-cultures were incubated onto the nanopillar gradients for
96 h. Fibroblast density was found to steadily decrease with increasing
nanopillar height, whilst endothelial cell density increased with pillar
height, with the exception of the highest pillars on the gradient. Here,
automated detection, measurement and classification of co-cultured cells
was employed for high-throughput analysis of cell phenomena.
Al roughness gradients produced by the use of sandblasting and chemical
polishing which systematically removed small features from the surface were
first described by Kunzler et al.
25,111
on an aluminium substrate. However,
this technique can be extended to many other substrates through the use of
templating,
111
whereby a negative impression is created using poly-
vinylsiloxane and subsequently a positive replica using an epoxy is formed.
These epoxy roughness gradients can then be used as is or coated with
metals or a specific chemical functionality can be imparted on the surface. Al
roughness gradients were subsequently incubated with osteoblast and
fibroblast cells for 1-7 days to determine preferential cell response based on
surface roughness.
25
In this study, it was found that osteoblasts showed
preferential treatment towards a surface roughness of around 6 mm after
4 and 7 days incubation. The fibroblasts however were found to favour the
smoother end of the gradient (roughness
d
n
3
r
4
n
g
|
7
.
1 mm) which is also in agree-
ment with published literature.
155,156
From these examples, it is obvious that
a generic assumption can not be made as to the optimum surface charac-
teristics of a surface for maximum cell response, and that each cell type will
B
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