(Top) Spray-coated PEDOT:DS slide laser machined to selectively remove the polymer layer. (Bottom) Chemical structure of PEDOT:DS. (Courtesy of Gordon G. Wallace.)
(Top) Spray-coated PEDOT:DS slide laser machined to selectively remove the polymer layer. (Bottom) Chemical structure of PEDOT:DS. (Courtesy of Gordon G. Wallace.)

A novel conductive, easy-to-process polymer synthesized by researchers at the University of Wollongong in Australia could be promising for bio-applications [Harman, D. G., et al., Acta Biomaterialia (2014), DOI: http://dx.doi.org/10.1016/j.actbio.2014.11.049].

Conductive polymers have the potential to serve as the interface between electronics and biological tissue in biomedical devices. Organic electronic materials are particularly attractive for this application because of their structural similarity to the molecules that make up biological tissue such as proteins, carbohydrates and nucleic acids, say researchers. The ideal material needs to be highly conductive, low toxicity, easy to prepare, and inexpensive to process. The Australian team, led by Gordon G. Wallace, believes that the novel material they have synthesized – a complex of the well-known polymer poly-3,4-dioxythiophene (or PEDOT) and sulfonated polysaccharide dextran sulfate (DS) – could be an ideal candidate.

“We have an ongoing interest expanding the materials inventory available to the bionics engineer to enhance the performance of existing implants such as the bionic ear and nerve stimulators to control the symptoms of Parkinson’s disease,” explains Wallace.

PEDOT:DS is easy to synthesize chemically in a single reaction, with the biomolecule DS effectively acting as a dopant or active additive. The resulting polymer can be readily processed using a range of fabrication tools. Just placing a small amount of the suspension onto a glass slide and leaving to dry can create a simple drop cast film of PEDOT:DS. PEDOT:DS can also be added to ethylene glycol for spray coating onto a glass surface. These approaches can be used to coat large areas of substrate, but more intricate structures are also possible.

Thin films of PEDOT:DS can be etched into patterns using laser ablation or printed directly onto a substrate. An aqueous dispersion of the versatile polymer can be formulated for use in an inkjet printer or a more viscous suspension can be created for extrusion printing. The researchers demonstrate inkjet printed patterns with 50 µm line widths spaced 500 µm and sub-centimeter multilayer structures fabricated by the extrusion method. Further refinement should be possible, say the researchers.

The synthesized PEDOT:DS has a unique set of attributes for an organic polymer – electronic conductance, electrochemical activity, and cytocompatibility. This new member of the polythiophene family shows great potential for biological applications such as the electrostimulation of cells, say the researchers.

“Our immediate target application is the development of new electrodes for neural recording and stimulation, [which] would have application in epilepsy detection and control,” says Wallace. “New materials like this could also enable regenerative bionic devices such as conduits for nerve or muscle repair to be developed.”