Bioactive Conducting Polymers for Optimising the Neural Interface - Biointerfaces: Where Material Meets Biology - page 215

Green et al. fabricated conducting hydrogels with substantially inter-
penetrating networks using a two-component biosynthetic hydrogel with co-
valently incorporated dopant. 10 The gel component consisted of 18 wt%
poly(vinyl alcohol) (PVA) and 2 wt% heparin (highly anionic glycosaminogly-
can), cross-linked together using methacrylate functional groups and photo-
initiated polymerisation. Covalent incorporation of the dopant throughout
the hydrogel guided the nucleation and deposition of PEDOT within the gel
during electrodeposition. The resulting conducting hydrogel had a slight in-
crease in impedance and approximately half the CSC of conventional PEDOT/
pTS electrodes, but retained a considerable electrical improvement compared
to bare platinum electrodes. The conducting hydrogels were found to be
capable of supporting PC12 cell attachment and neurite growth.
The electrical properties of conducting hydrogels can be improved
through nanostructuring of the polymer hybrid. Baek et al. fabricated
nanostructured thin film conducting hydrogels by depositing PEDOT/pTS
around poly(2-hydroxyethyl methacrylate) brushes which had been bound to
the surface of a gold electrode via surface initiated atom-transfer radical-
polymerisation. 57 The hybrid material was found to have increased CSC and
neural cell growth (PC12 cell line) compared to conventional PEDOT/pTS.
Research on conducting hydrogels is still in its infancy; moving forward
key areas of research involves investigating the role of the dopant and
interaction between the two polymer components during polymerisation
and the affect these have on the resultant composite structures and prop-
erties as well as the role of biofunctionality within conducting hydrogels.

d n 3 r 4 n g | 2

8.5 Conclusion
Conducting polymers are a promising alternative to bare metal electrodes for
use in neuroprosthetic devices and are an enabling technology for biosensors
and nerve guides. They have been proven to be beneficial in functional in vivo
tests. Imparting biofunctionality to conducting polymer coatings through
incorporation of biologically active molecules has the potential of creating
high quality neural interfaces for electrical recording and stimulation of
neural tissue. However, major challenges exist in the development of bioac-
tive conducting polymers such as balancing biofunctionality with electrical
and mechanical stability. Several approaches to overcoming these limitations
have been developed. Creating conducting polymer composites, such as
conducting hydrogels allows for the development of electrode coatings with
all the benefits of bioactive conducting polymers while maintaining electrical
and mechanical stability, providing a material platform for the creation of
high quality neural interfaces for next-generation neuroprosthetic devices.

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A Appendix: Methodologies and Practical Advice
The following section details methods commonly used by the authors in the
fabrication and characterisation of conducting polymers with a focus on
providing practical advice for these methods.