Bioactive Conducting Polymers for Optimising the Neural Interface - Biointerfaces: Where Material Meets Biology - page 203

Because conducting polymers are softer than metal electrodes they ex-
perience less strain mismatch at the interface. 10,22 Strain mismatch is a
contributing factor for chronic inflammation so it is desirable to use elec-
trode materials with mechanical properties closer to that of neural tissue.
The highly textured, nodular surface morphology not only helps to provide
conducting polymers with superior electrical properties, but it may also
provide a preferable surface for soft tissue integration. Several studies have
shown that neural cells will preferentially adhere to coated electrodes. 3,24-26

d n 3 r 4 n g | 2

8.2.4.2 Drug Delivery Systems
Depending on the size and charge of an incorporated bioactive molecule it is
possible for conducting polymer electrodes to also act as controlled drug
delivery devices. 5,27 If the bioactive molecule is mobile within the con-
ducting polymer it can be released in a controlled fashion via electrical
stimulation. This is discussed in greater detail in Section 8.3.3.

8.2.4.3 Nerve Grafts/Conduits
Nerve grafts are devices designed to repair or bridge a defect in neural tissue.
The most common application is nerve conduits for spinal injury, however,
nerve grafts can also be used to repair damage in the peripheral nervous
system. The formation of an ordered, effective neural conduction path is the
key goal of nerve grafts. Conducting polymers are a promising material
platform for nerve grafts because their electroactivity can be used to not only
guide the directional growth of neural cells but to also encourage neurite
outgrowth. Schmidt et al. have demonstrated the use of PPy in the fabri-
cation of a nerve guidance channel which showed favourable interactions
with PC12 cells and chicken sciatic nerve explants. 28 Furthermore, the PPy
guidance channels were able to promote a significant increase in neurite
outgrowth by stimulating the cells with a 100 mV potential for 2 h. Many of
the goals and approaches discussed in this chapter hold true for conducting
polymers in nerve graft applications.

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8.2.4.4 Biosensors
Biosensors are analytical electrodes designed to detect specific molecules of
interest in applications ranging from health care to environmental moni-
toring. 29 In these biosensors the conducting polymer is used as a matrix for
the entrapment of biomolecules which act as a sensing element, chosen due
to their biorecognition of the analyte (the molecule to be detected). Inter-
action between the sensing element and the analyte results in a chemical
change that is detected by the conducting polymer matrix. The conducting
polymer acts as a transducer converting the chemical signal into an electrical
signal from which the concentration of analyte can be determined.