Bioactive Conducting Polymers for Optimising the Neural Interface - Biointerfaces: Where Material Meets Biology - page 207

8.3.1.1 Incorporation of Charged Biomolecules as Dopants
As stated previously, the presence of a charged dopant molecule is required
during electrochemical deposition in order to form a functional conducting
polymer. If the biomolecule of interest has one or multiple sites of ionic
charges (dopant groups) then it can be electrostatically incorporated within
the conducting polymer as a dopant. There is typically one dopant group
associated with every three to four monomer units, and as such the bioactive
dopant needs to be supplied at a high enough concentration within the
electrolyte precursor solution to ensure successful polymerisation. 5 Large,
bulky, biological dopants may experience mass transport limitations during
polymerisation resulting in a concentration deficit at the deposition inter-
face, interfering with the electrodeposition process. 3,33
A critical aspect of creating bioactive conducting polymers is the retention
of the dopants biofunctionality. In particular, biofunctionality may be
compromised during electrodeposition due to chemical or electrical de-
naturation as a result of the organic solvents and electrical charge used
during electrodeposition.

d n 3 r 4 n g | 2

TIP: Both PPy and PEDOT can be fabricated from aqueous solutions in the
absence of organic solvents. Unlike PPy, PEDOT has very poor solubility in
water (the authors typically use a 1 : 1 water-acetonitrile solution for PEDOT
when organic solvents are not a concern). Due to the low concentration of
PEDOT in aqueous solutions, low current densities should be used during
deposition to avoid mass-transport limitations.

.

Also of critical importance is the effect of dopant choice on the properties
of the resultant conducting polymer film. 7 The three main factors deter-
mining conducting polymer properties are choice of monomer (conducting
polymer chemistry), electrodeposition parameters (solvent, pH, current
density, time) and choice of dopant. As such, when using bioactive dopants
there is typically a trade-off between biofunctionality and dopant ecacy.

8.3.1.2 Incorporation of Neutral and Weakly Charged
Biomolecules as Non-dopant Inclusions
There are three pathways through which bioactive molecules can be in-
corporated within conducting polymers as non-dopant inclusions; physical
entrapment within the polymer matrix or attachment to the polymer surface
through physical adsorption or covalent tethering. 3,26,34
Non-dopant bioactive molecules can be incorporated within conducting
polymer matrices through their inclusion in the electrolyte solution used for
electrodeposition. As the conducting polymer deposits on the electrode the
bioactive molecules present in the electrolyte become physically entrapped
within the polymer matrix as it forms. Incorporation of bioactive molecules
using this method can disrupt the formation of the conducting polymer,