Biomedical Engineering Reference
In-Depth Information
conducted at room temperature. In this method, a vapour of monomer
molecules are electrically excited to form a plasma phase; components of the
plasma phase (ions, radicals, and neutrals) then may oligomerise and de-
posit on the substrate placed in contact with the plasma.
180-182
Through the
use of low power and low pressure, functional groups in the monomer are
retained in the final deposited film, for example, carboxylic acid groups from
acrylic acid.
183
Chemical gradients displaying a single or several functional
groups can be easily prepared using plasma polymerisation. There have been
several methods reported for the preparation of plasma polymerisation
gradients in recent years including using an instrument termed a 'gra-
dientiser', where a mask shields part of the surface whilst the monomer
composition continuously changes,
109,110,184
using a knife edge electrode
whereby the chemistry changes with increasing distance from the elec-
trode,
185
and diffusion based depositions by shielding the surface with a
stationary mask,
7,186
A variety of terminal groups can be incorporated into
the gradient surface including, amino, carboxylic acid, methyl, aldehyde and
epoxy using these methods.
Two versions of the gradientiser have been produced. In the first method,
the sample was placed into a drawer as shown in Figure 10.12A.
109,184
Initially, a thin allylamine plasma polymer coating was deposited over
the entire substrate. A second monomer, acrylic acid, was then introduced
into the chamber while simultaneously reducing the flow of allylamine. Dur-
ing this process the drawer was slowly retracted. This resulted in a chemical
composition gradient from amine to carboxyl over a distance of 11 mm.
d
n
3
r
4
n
g
|
7
.
Figure 10.12 Various plasma polymerisation reactors for gradient preparation:
(A) gradientiser drawer;
109,184
(B) gradientiser slit mask;
110
(C) knife-
blade electrode;
185
(D) diffusion under a mask.
7,105
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