Biomedical Engineering Reference
In-Depth Information
creating these composites is to combine the electrical functionality of the
conducting polymer with the benefits of the other composite component.
Two such systems, conducting polymer-carbon nanotube composites and
conducting hydrogels are discussed below. Another class of composites
attracting increasing focus is that of degradable conducting polymer com-
posites. These are systems in which conducting polymers or oligomers are
used to form either composites or co-polymer blends for use in tissue en-
gineering and drug delivery. Readers are referred to Guo et al. for a more
detailed discussion of degradable systems.
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8.4.2.1 Conducting Polymer-Carbon Nanotube Composites
Carbon nanotubes (CNTs) can be incorporated within conducting polymer
electrodes to increase conductivity and electrostability while decreasing
electrical impedance.
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Conducting polymer-CNT composites are typically
fabricated via electrodeposition using a CNT-loaded electrolyte solution. In
addition to improved electrical properties, CNT composites can also be used
for controlled drug delivery.
Luo et al. deposited PPy around CNT that had been preloaded with dexa-
methasone.
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The PPy matrix encapsulated the CNTs and prevented the
passive release of dexamethasone from within. When simulated, the PPy-
CNT composites released larger and more sustained doses of dexa-
methasone compared to conventional PPy/dexamethasone films. Released
dexamethasone was found to retain its bioactivity as demonstrated by its
in vitro reduction of microglial (HAPI cell line) activation.
Concerns regarding the cytotoxicity of CNTs have been raised in the past;
however, studies have shown that incorporation of CNTs within conducting
polymer coatings does not result in cellular inhibition.
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This is likely due to
the fact that the CNTs are immobilised within the conducting polymer
matrix and as such have only very limited physical interaction (uptake) with
nearby cells.
.
8.4.2.2 Conducting Hydrogels
Hydrogels are cross-linked polymer networks that swell in aqueous en-
vironments due to their highly hydrophobic nature. Conducting hydrogels
are composites of conducting polymers and hydrogels integrated at the
molecular level. The goal of conducting hydrogels is to combine the elec-
trical functionality of conducting polymers with the mechanical and bio-
logical properties of hydrogels by creating interpenetrating polymer
networks.
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Hydrogels have mechanical properties akin to those of neural
tissue, reducing strain mismatch at the neural interface. Furthermore, the
use of conducting polymer-hydrogel composites may avoid the degradation
of mechanical properties upon incorporation of bioactive molecules such as
that experienced by conventional conducting polymers. Due to the open,
swollen hydrogel network, conducting hydrogels can accommodate larger
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