Conducting polymers biocompatibility

The presence of polymer, solvent, and ionic components in conducting polymers reminds one of the composition of the materials chosen by nature to produce muscles, neurons, and skin in living creatures. We will describe here some devices ready for commercial applications, such as artificial muscles, smart windows, or smart membranes other industrial products such as polymeric batteries or smart mirrors and processes and devices under development, such as biocompatible nervous system interfaces, smart membranes, and electron-ion transducers, all of them based on the electrochemical behavior of electrodes that are three dimensional at the molecular level. During the discussion we will emphasize the analogies between these electrochemical systems and analogous biological systems. Our aim is to introduce an electrochemistry for conducting polymers, and by extension, for any electrodic process where the structure of the electrode is taken into account. 

The direct electrochemistry of redox proteins has developed significantly in the past few years. Conditions now exist that permit the electrochemistry of all the proteins to be expressed at a range of electrodes, and important information about thermodynamic and kinetic properties of these proteins can be obtained. More recently, direct electron transfer between redox enzymes and electrodes has been achieved due to the more careful control of electrode surfaces. The need for biocompatible surfaces in bioelectrochemistry has stimulated the development of electrode surface engineering techniques, and protein electrochemistry has been reported at conducting polymer electrodes 82) and in membranes 83, 84). Furthermore, combination of direct protein electrochemistry with spectroscopic methods may offer 85) a novel way of investigating structure-function relationships in electron transport proteins. 

Tang and co-workers used leucine-functionalized phenyl acetylene derivatives for the construction of amphiphilic helical polymers, which were envisioned to be both semi-conducting and biocompatible, leading to diverse applications such as biosensors [36]. The polymerization was performed with a rhodium catalyst and resulted in high molecular weight polymers, particularly for polyacetylene la (1.5 10 g/mol). Interestingly, only the polymers in which the stereo-center was closely located to the helical backbone (la and lb) showed a CD signal and were optically active (Fig. 6). 

A review of micro-electromechanical systems (MEMS)-based delivery systems provides more detailed information of present and future possibilities (52). This covers both micropumps [electrostatic, piezoelectric, thermopneumatic, shape memory alloy bimetallic, and ionic conductive polymer films (ICPF)] and nonmechanical micropumps [magnetohydrodynamic (MHD), electrohydrodynamic (EHD), electroosmotic (EO), chemical, osmotic-type, capillary-type, and bubble-type systems]. The biocompatibility of materials for MEMS fabrication is also covered. The range of technologies available is very large and bodes well for the future. 

CPs designed for biomedical applications generally require good electrical conductivity, physicochemical and mechanical stability, and biocompatibility to effectively interact with biological system. A wide range of analytical techniques to characterize the feasibility of conducting polymers as biomaterials are summarized here. 

Biocompatible electromechanical actuators composed of silk-conducting polymer composites. Adv. Funct. Mater. 24,3866-3873. 

Due to the inherent conductivity and electroactivity of conducting polymers, they act as suitable substrates for the in vitro stucfy of excitable cells, including skeletal muscle cells. Biocompatible conducting polymers, such as polypyrrole, polyaniline, and PEDOT, have been used as substrates for the culture of a range of cell types, including PC12 cells, endothelial cells, fibroblasts, and keratinoqftes. 

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