Fabrication of Nanostructured Conductive Polymers

CPs can be fabricated through a variety of routes which are classified as either predominantly electrochemical or chemical. While electrochemical synthesis has been more widely used for preparing nanoscale CP thin films for biomedical applications, chemical polymerization can produce large quantities of CP thick films or colloidal dispersions at low cost. Despite these advantages, chemical techniques have found relatively little application in biomedical applications. The advantages and disadvantages of electrodeposition and chemical synthesis are summarized in Table 18.2. 

The main advantage of electrodeposition is its simplicity and reproducibility. CP thin films of controlled thickness and morphology can be electropolymerized on conductive surfaces, conventionally platinum, gold, or indium tin oxide (ITO), by varying the applied number of charges passed through the electrolyte solution. However, not all CPs can be formed electrochemically. For efficient electropolymerization, the chosen monomer must be able to readily oxidize into its radical cation at the potential applied to the electrolyte. 

Eleetrodeposition Short polymerization time ( 15 min) Ease of set up Uniform thin film (20 nm-100 pm) on conducting surface (control of film thickness) Ability to entrap/dope biological entities into polymer matrix Limited number of processible monomers Inability to coat nonconducting surface Minimal control over the molecular weight (MW) and the structural features 

Chemical Synthesis Flexibility of polymerization scheme Coatings of nonconducting surfaces Control over the MW and the structural features Post-processi bi 1 ity Mass-producibi 1 ity Complexity of fabrication process Powdery end product (requires post-processi ng) Intricacy of incorporating complex bulky dopant Use of oxidants 

However, dopant solubility and pH level must be considered, as these are also dependant on the choice of solvent. As mentioned previously, conventional sodium sulfonate dopants and anionic biomolecules are easily dissolved in water. Aqueous sodium sulfonate electrolytes have a pH range (pH 7-9) close to the body pH level and this would help to minimize pH-induced cytotoxicity when implanted in the body. Temperature can affect the solubility of dopant and even the viscosity of electrolyte. Generally, low temperature helps to produce smoother, more conductive films, but the reduced dopant solubility and the increased viscosity can be problematic [62]. 

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