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Conductive polymers (Polyheretocycles (Polypyrrole (PPy) (Pros (Good in…
Conductive polymers
Polyheretocycles
Polypyrrole (PPy) 
Pros
- Good in vitro and in vivo biocompatibility - supports the growth of a large variety of cell types, including keratocytes
- No significant long term effect in vivo
- Minimal tissue response
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:warning: Repeated steps of rinsing and extraction to remove impurities, reactants, monomers and short oligomers are needed for the polymer to be completely cytocompatible
Cons
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non-thermoplastic, mechanically rigid and brittle
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Dopants: DS (dextran sulphate), PMAS, pTS, HA (hyaluronic acid), CS (chondroitin sulphate)
Polyaniline (PANI)/ aniline black
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Polythiophenes (PTh)
Derivatives
PEDOT
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Dopants: PSS, heparin, nerve growth factor (NGF), HA and fibrinogen
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Notes
:warning: Doping with biomolecules could have negative side effects (disrupt the mechanical stability and long term electrochemical performance):
- Collagen was responsible for bad film integrity
- HA reduced the electrical conductivity
:green_cross: The concentration of biomolecules within the polymer is limited ->reduced amount of signal presented/released from the CP matrices.:check: it is possible to improve the biocompatibility of the system through bonding biocompatible molecules, segments and side chains :green_cross: The dopants and the synthesis conditions (i.e. not only the material) might affect cell behaviour since it changes the surface topography of the polymer:check: Reduced biocompatibility can result from small amount of dopants and low molecular weight products leaking out from the polymer - purification needed!:warning: Fatigue of conductive polymers with repeated cycles of electrical stimulation - the continuous movement of doping agents in and out the polymer and the swelling and deswelling causes cracks, delamination and overall degradation. Eg. a PPy/PPS composite retained only 5% of its original conductivity after the application of 0.4V for 16h.
Synthesis
Electrochemical
System
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three-electrode cell
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Upon application of an electric potential, the CP monomers are oxidised to radical cations and form positively charged films with anionic doping on the working/positively charged electrode
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Conductive hydrogels
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CPs deposited within a hydrogel matrix
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:warning: the hydrogel and the CP should be completely intergrated in an interpenetratin network (IPN)
:warning: The first step in combining materials is ensure that they are miscible. CPs can range from hyrophobic to hydrophilic
:red_cross: Large mesh sizes/open structure is advantageous for transport and diffusion and is helpful while trying to load or swell the CP in the hydrogel network. However, it also means that is plenty of room to migrate out of the hydrogel
:no_entry: Electrochemical synthesis - there is a strong tendency for the CP diffuse through the hydrogel and form directly on the electrode surface
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w/ electrical potential
dopants start to move in an out the polymer disrupting the backbone - the charge passes through the polymer
Dopant + charge = polaron
Polaron travels along the chain causing a distortion of the crystal lattice
Introduces a charge carrier in the system by removing (p-doping) or adding (n-dpoing) electrons from the polymer chain
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The size and amount of dopants greatly affect the polymer properties:
- Surface roughness
- Wettability
- Morphology
- Stiffness
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Coating
Coat the electrospun fibers with the conductive polymerEg. PPy- PLGA fibersPPY - coated fibroin fibers
- black silk mesh
- PPy improved the mechanical properties
- Cells grew better on uncoated mats :red_cross: PPy may had contaminants from the synthesis
Blends
Blend the conductive polymer with a carrier (e.g. PEG) before the electrospinning process
E.g. PANI + PCL
PANI + PLCL
PANI + gelatine
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NPs
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e.g. PPy particles dispersed in insulating PDLLA continous phase
- Emulsion polymerization
- PPy non degradable and the cell viability was decreased in the presence of PPy comparing with controls - keep the content of PPy as low as possible
:warning: Deterioration of PPy in H2O - dedoping and deprotonation