Bioactive Conducting Polymers for Optimising the Neural Interface - Biointerfaces: Where Material Meets Biology - page 201

allowing the dopant to diffuse out into the surrounding environment.
Therefore it is important to consider the toxicity and mobility of dopant ions
within biomedical applications. Biomedical conducting polymers such as
polypyrrole (PPy) and poly(3,4-ethylenedioxythiophene) (PEDOT) have gen-
erally been found to be non-cytotoxic materials. 14
Other in vitro assays will examine more application specific cellular re-
sponses. Perhaps the most common is culturing PC12 neural-like cells and
analysing cell and neurite density. 14 Other models used include primary
neural tissue explants, typically neurons and glial cells. 15-17 Studies have
shown that a range of factors affect in vitro neural cell response to con-
ducting polymers, including synthesis technique, film roughness and
morphology as well as dopant chemistry and mobility. 3

d n 3 r 4 n g | 2

TIP: PC12 is a non-adherent cell line which will differentiate and grow
neuronal processes when cultured in low-serum media and exposed to nerve
growth factor. Samples will require coating with either laminin or poly- L -ly-
sine to facilitate cellular attachment. When plating, PC12s are moved from
high-serum media (RPMI þ 10% horse serum þ 5% foetal bovine serum) to a
low serum media (RPMI þ 1% horse serum) containing 50 ng mL 1 nerve
growth factor, plating at 20 000 cells cm 2 . Media is refreshed at 48 h and
samples are imaged at 96 h. Neurite density can be determined by tracing
neurites in ImageJ software (National Institutes of Health) using the NeuronJ
plugin.

In vivo characterisation conventionally involves implantation studies
assessing electrical recording and stimulating capabilities as well as histo-
logical examinations of the tissue-electrode interface within the central
nervous system to characterise the biological response to implantation. 18-20
For a more in-depth review of in vivo studies of conducting polymers the
reader is referred to Ateh et al. 21

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8.2.4 Biomedical Applications of Conducting Polymers
Conducting polymers are being investigated for a variety of applications
within the field of biomedical engineering including stimulating-recording
electrodes, electrically controlled drug-release systems, biosensors and nerve
grafts and conduits. Due to the high demand for the chemical and electrical
stability for these applications, heterocyclic compounds such as PPy and
polythiophenes, whose chemical structure are illustrated in Figure 8.7, are
favoured for biomedical applications. 4 A range of molecules are used as
conventional dopants for biomedical applications, including p-toluene-
sulfonate (pTS), polystyrenesulfonate (PSS) and perchlorates. 14
The focus of research concerning biomedical conducting polymers falls
heavily on their use as neuroprosthetic electrode coatings; however, con-
ducting polymers have also shown great promise in applications such as
controlled drug delivery systems, nerve grafts/conduits and biosensors.