Biomedical Engineering Reference
In-Depth Information
be included. Four commonly used methods are described highlighting their
advantages and disadvantages as well as specific factors that affect the
grafting outcome. This chapter will not detail the 'grafting to' approach in
which a pre-formed polymer is attached to a functional group on a surface
nor will it include syn-grafting of monomers adsorbed to a substrate prior to
plasma treatment; for these topics the reader is referred to excellent re-
views.
2,6,7
Furthermore, the focus will be on monomers carrying functional
groups that can impart a charge to the surface and/or be used for subsequent
attachment of biomolecules. When grafting of functional monomers to
biomaterials it is important to properly characterise the modified substrate
before evaluation of the in vitro or in vivo responses. Without such charac-
terisation the interpretation of biological data is not warranted. Thus, the
second half of this chapter is dedicated to various aspects of characterisation
of grafted substrates as well as the grafted chains themselves and their
position in/on the polymer substrate.
d
n
3
r
4
n
g
|
2
11.2 Methods for Grafting of Functional Monomers
Surface grafting of functional monomers can be employed to tailor the
surface properties leading to new molecular functionalities incorporated
onto an activated polymer surface. The four methods considered are: (1)
simultaneous grafting method (Scheme 11.1A); (2) peroxy/hydroxyl grafting
(Scheme 11.1B); (3) grafting from a surface using CRP (Scheme 11.1C); and (4)
plasma polymerisation (Scheme 11.1D). Each method has its advantages and
disadvantages, and in addition, different polymer topology (architecture) and
polymer chemistry of the grafted chains will result from the different meth-
ods. Detailed descriptions of these methods are given in Sections 11.2.1 to
11.2.4. Furthermore, grafting of functional monomers to porous substrates
such as membranes and tissue engineering scaffolds require an additional
set of considerations and will be described separately in Section 11.2.5.
Depending on the purpose of the surface modification, different
monomers can be used to introduce various functionalities to a substrate
surface. The most commonly explored charged functional groups of
carboxyl (-COOH), amine (-NH
2
), phosphate (-O-P(O)(OH)
2
), and sulfate
(-O-S(O)(OH)
2
) will be discussed. In addition, included will be functional
groups suitable for attachment of biological molecules, i.e., aldehyde
[-CH(O)] and epoxy (-CHOCH
2
).
4
Examples of monomers employed for
grafting of these functional groups on polymer substrates will be given in the
following individual sections.
.
11.2.1 Simultaneous Grafting
In the simultaneous grafting technique (Scheme 11.1A), the polymer sub-
strate and monomer (a vinyl compound) are subjected simultaneously to
radiation. The monomer is typically dissolved in a solvent which does not
dissolve the polymer substrate. Oxygen, which is an inhibitor, is eliminated
Search WWH ::
Custom Search