Biomedical Engineering Reference
In-Depth Information
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Figure 10.14
Schematic for the preparation of co-polymer brush gradients:
(A) solution draining method; (B) resultant polymer molecular weight
gradient; (C and D) complete submersion to generate co-polymer
brush gradient of varying lengths; (E and F) second solution draining
procedure to create a co-polymer brush gradient of varying polymer
ratios but the same thickness.
Figure adapted from Tomlinson et al.
98
This work was pioneered by Tomlinson and Genzer who developed several
methods of preparing polymer brush-like gradients, as summarised in
Figure 10.14.
202,203
A solution draining method was prepared to induce a
gradual change in molecular weight, involving submersing a uniformly de-
posited initiator substrate into a monomer solution and slowly draining the
monomer solution (Figure 10.14A and B). Subsequently, the gradient was
completely submerged in a second monomer solution to create a co-polymer
brush gradient of varying lengths (Figure 10.14C and D). Alternatively, a
second solution draining procedure could be implemented to generate a co-
polymer brush gradient of varying polymer ratios (Figure 10.14E and F).
These methods have been readily utilised to prepare 2-dimensional (2D)
gradient surfaces.
Several modifications to these processes were developed. Xu et al.
204
de-
scribed a method whereby a monomer solution was slowly injected into one
end of the initiator functionalised substrate using a syringe pump and
microchannel system (Figure 10.15A), with polymerisation times varying
according to the monomer incubation time. This method resulted in a
homopolymer molecular weight or a block co-polymer gradient. In another
experiment, a microfluidic static mixer was employed to mix two monomer
solutions with constantly ratios of monomer A and monomer B
(Figure 10.15B).
97
Following UV polymerisation, the result was a gradient in
the composition of the polymer brush, with a gradual variation from
monomer A to monomer B.
An alternative method, originally designed for
.
the preparation of
alkanethiol gradients
involves a simple dip-coating process
into a
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