Biocompatibility implications of polypyrrole synthesis techniques

Abstract

Polypyrrole (PPy) is an inherently conducting polymer that has shown great promise for biomedical applications within the nervous system. However, to effectively use PPy as a biomaterial implant, it is important to understand and reproducibly control the electrical properties, physical topography, and surface chemistry of the polymer. Although there is much research published on the use of PPy in various applications, there is no systematic study linking the methodologies used for PPy synthesis to PPy's basic polymeric properties (e.g., hydrophilicity, surface roughness), and to the biological effects these properties have on cells. Electrochemically synthesized PPy films differ greatly in their characteristics depending on synthesis parameters such as dopant, substrate, and thickness, among other parameters. In these studies, we have used three dopants (chloride (Cl), tosylate (ToS), polystyrene sulfonate (PSS)), two substrates (gold and indium tin oxide-coated glass), and a range of thicknesses, to measure and compare the biomedically-important characteristics of surface roughness, contact angle, conductivity, dopant stability, and cell adhesion (using PC-12 cells and Schwann cells). As predicted, we discovered large differences in roughness depending on the dopant used and the thickness of the film, while substrate choice had little effect. From contact angle measurements, PSS was found to yield the most hydrophilic material, most likely because of free charges from the long PSS chains exposed on the surface of the PPy. ToS-doped PPy films were tenfold more conductive than Cl-or PSS-doped films. X-ray photoelectron spectroscopy studies were used to evaluate dopant concentrations of PPy films stored in water and phosphate buffered saline over 14 days, and conductance studies over the same timeframe measured electrical stability. PSS proved to be the most stable dopant, though all films experienced significant decay in conductivity and dopant concentration. Cell adhesion studies demonstrated the dependence of cell outcome on film thickness and dopant choice. The strengths and weaknesses of different synthesis parameters, as demonstrated by these experiments, are critical design factors that must be leveraged when designing biomedical implants. The results of these studies should provide practical insight to researchers working with conducting polymers, and particularly PPy, on the relationships between synthesis parameters, polymeric properties, and biological compatibility.

Tunable conjugated polymers for bacterial differentiation

“…Water contact angle is a parameter which indicates the hydrophobicity of surface materials. These data are in agreement with other reports which indicate the role of the dopant in the wettability of polypyrrole [20]. The redox state altered the hydrophobicity of the polymer surfaces, but the impact of this effect varied due to the type of dopant.…”

“…Since the mass amount of electro-polymerised polypyrrole is directly proportional to the amount of charge passed during synthesis, all samples were equal with respect to the amount of polypyrrole. On the other hand, the thickness of polymer is related to the charge passed, surface area of the working electrode and the density of final product [20]. Because in this case the charge and surface area were fixed in all samples, the difference in thickness is related to the contribution of each dopant in the final mass product and/or the different density of each polymer type.…”

“…Surface properties of these very well studied polymers can be effectively controlled and reproduced by controlling the polymerisation conditions as well as by using appropriate counter ions. The use of various types of dopants in combination with different polymerisation conditions influences polymer surface properties like thickness, roughness, conductivity and hydrophobicity [20][21][22] and has been shown to influence cell viability [18].…”

The selective detection of dopamine at a polypyrrole film doped with sulfonated β-cyclodextrins

“…The thickness of the films was also theoretically calculated as 600 nm from the total charge passed using a relationship derived by Diaz et al [31] that assumes that 1 C cm −2 is equivalent to 2.5 m of polymer growth. This is slightly higher than the experimental analysis however, it is important to highlight that the relationship quoted by Diaz et al [31] was for a simple chloride dopant, which has been shown to form thicker films than polypyrrole films doped with tosylate and polystyrene sulfonate when the same amount of charge has been passed [32]. The values obtained from both the experimental and theoretical analyses indicate that the polypyrrole sulfonated ␤-cyclodextrin films are porous and may exhibit thin film diffusion.…”

Future Applications of Electronic-Nose Technologies in Healthcare and Biomedicine

“…A hydrogel synthesized from a poly(HEMA)-based hydrogel and poly(aniline was fashioned into a biosensor (by incorporation into recombinant cytochrome P450-2D6) that was responsive to the drug fluoxetine, the active ingredient in Prozac (Iwuoha et al, 2004). These polymeric materials provide a non-cytotoxic interface between the biosensor device and native living tissue or cell culture medium (Fonner et al, 2008). Gawel et al (2010) reviewed the various principles involved in the design of biospecific hydrogels acting through various molecular mechanisms to transduce the recognition of label-free analytes.…”