Biomedical Engineering Reference
In-Depth Information
This gradient preparation method is versatile in that by changing the
monomer solutions, many functional groups can be deposited onto the sur-
face in this manner.
In the second version, the sample is placed into the reaction chamber with
a thin slit mask placed over the top at one side of the sample
(Figure 10.12B).
51,65,110,187,188
The monomer composition is gradually
changed from one monomer to another, whilst the slit is very slowly moved
across the sample. This method has advantages over the first generation of
its type as the thickness of the plasma polymer is relatively consistent. Parry
et al.
184
prepared a graded acrylic acid (AA) to octadiene (OD) chemical
gradient. Immunoglobin G (IgG) was adsorbed onto the plasma polymer
gradient and it was observed that more IgG was adsorbed at the octadiene
end (4200 ng cm
2
) compared to the acrylic acid end (
o
20 ng cm
2
).
Another approach is the use of a stationary knife blade electrode as de-
scribed by Menzies et al.
185
d
n
3
r
4
n
g
|
7
(Figure 10.12C). A knife blade was positioned
B
1 mm above the substrate and a gradient of diethylene glycol dimethyl
ether (DG) plasma polymer was deposited due to the non-uniform plasma
glow discharge. A variation in both the thickness and chemical composition
was achieved, with the ether component (O-C-O) gradually decreasing at
increasing distances from the knife-blade electrode. The DG plasma polymer
produces a PEO-like coating minimising protein and cell attachment.
189
Hence, a gradient from a high cell-binding surface to a low cell-binding
surface could be formed in this manner. Adsorption of BSA and lysozyme
onto the PEO-like plasma polymer gradients was assessed by XPS and
TOF-SIMS analysis.
17
Zelzer et al.
7
prepared thickness gradients via diffusion-controlled plasma
polymerisation (Figure 10.12D). Gradients ranging from chemistry based on
allylamine plasma polymers to hexane plasma polymers were prepared on
glass through diffusion under a fixed mask. Sharp and shallow gradients
were prepared depending on the distance between the mask and substrate.
Once again, a sigmoidal curve of film thickness was observed. The wett-
ability ranged from hydrophobic at the hexane plasma polymer end to
hydrophilic at the allylamine plasma polymer end of the gradient. NIH 3T3
fibroblasts were seeded on the surface with the highest cell attachment
observed at the hydrophilic acrylic acid end of the gradient. One concerning
observation was that a significant difference was observed in the cell density
per surface area between the allylamine end of the gradient and a uniform
allylamine plasma polymer control. This result demonstrates the need for
simultaneous uniform substrates in conjunction with gradient materials.
Using a similar technique, Harding et al.
105
generated a plasma polymer
gradient varying form cell adhesive acrylic acid to cell repellent diethylene
glycol dimethyl ether (DG). In this instance, a glass mask was tilted at 121 to
the substrate with the sides enclosed. Detailed methods for the preparation
of plasma polymer gradients are described below. Mouse embryonic stem
cells were incubated on the AA-DG gradients for 3-5 days with both colony
size and colony morphology correlating with the continued expression of
.
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