Grafting of Functional Monomers on Biomaterials - Biointerfaces: Where Material Meets Biology - page 325

polymer causing dissolution upon exposure to a solution. 4 It is therefore
essential to optimise the conditions for each monomer. Another concern
regarding plasma polymers is their instability in air and ageing phenomena
have been studied extensively; the reader is referred to an excellent review
covering the topic. 1
In contrast to the previously described methods the monomers used dur-
ing plasma polymerisation do not need to contain a vinyl group. For example,
for the introduction of amine groups heptylamine (an aliphatic amine) and
allylamine (a vinyl monomer) can both be applied. While heptylamine
undergoes fragmentation and recombination reactions only, allylamine dis-
play higher deposition rates and this is attributed to additional conventional
radical polymerisation taking place concomitantly for this monomer. 1 Like-
wise, the vinyl monomer AA has a significantly higher deposition rate than
propanoic acid, again attributed to the additional conventional radical
polymerisation. Moreover, this leads to plasma polymers produced from AA
displaying a more linear chain structure than that obtained from saturated
monomers like propanoic acid. 1 Optimisation of the density of functional
groups can be achieved by careful selection of the monomer. For introduction
of amine groups it has thus been found that the use of diaminocyclohexane
yields a higher density than heptylamine. 1 In addition to introduction of
carboxyl 70,71 and amine 72-74 groups, plasma polymerisation also provides a
convenient avenue for the introduction of epoxide 75 and aldehyde 72,76 func-
tionalities. The reader is referred to specific papers given above for a guide to
optimal plasma parameters for each monomer considering the required
optimisation for each plasma reactor type.

d n 3 r 4 n g | 2

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11.2.5 Grafting of Functional Monomers to Porous
Substrates
There is a great interest in membranes and 3D scaffolds for biomedical
applications. 77-79 3D scaffolds can be fabricated by a range of methods in-
cluding supercritical fluid technology, rapid prototyping, porogen leaching
and phase separation techniques (e.g., thermally induced phase separation
(TIPS)). In addition, membranes can be fabricated by different techniques
with electrospinning being one of the popular approaches used for tissue
engineering constructs. Each of these methods allow for fabrication of
scaffolds/membranes with different overall porosity and different pore sizes
and shapes. The pore tortuosity (a description of how many turns the pores
have) will also depend on the fabrication method used. While studies in-
vestigating grafting of functional monomers on membranes are common,
similar studies on 3D scaffolds have mainly appeared in recent years.
One aspect that must be taken into account when grafting of functional
monomers to porous substrates is whether the method and conditions
chosen will allow modification throughout the interior of the porous