The ability to interface with neural tissues is enabling a new range of health interventions. Applications include pacemakers, deep brain stimulators for treating Parkinson's disease, cochlear implants, functional artificial limbs and smart contact lenses.

An obvious key to these interactions is an effective and reliable means for establishing a connection between an electrode and the neural tissue.

A research team at the University of Delaware looked into the possibility of using a conjugated polymer known as PEDOT — poly (3,4-ethylene dioxytheopine).

David Martin, University of DelawareDavid Martin, University of DelawarePEDOT has been widely used in applications such as energy conversion and storage, organic light emitting diodes (OLEDs), electrochemical transistors, and sensors. The problem is that conjugated polymers have low mechanical stability and relatively limited adhesion on solid substrates. This can limit the lifetime and performance of the devices and cause mechanical failure that might leave behind undesirable residue in the tissue.

The Delaware team has developed a method of electrografting that enhances the adhesion. It is a process in which organic molecules are electrochemically oxidized or reduced, followed by the formation of a high quality electrically conductive metal-organic bond at the substrate-polymer interface.

In this video, team leader David Martin draws an analogy with Teflon coatings on frying pans. It is straightforward that food will not stick to the Teflon coating. The real technical challenge was to get the Teflon to stick to the metal pan and to make sure that the coatings will not peel off or crack.

Not only is the adhesion effective with this technique, but the process takes just minutes, whereas similar approaches require multiple steps. It is also effective with a variety of substrate materials including gold, platinum, glassy carbon, stainless steel, nickel, silicon and metal oxides.

"Our results suggest that this is an effective means to selectively modify microelectrodes with highly adherent and highly conductive polymer coatings as direct neural interfaces," says Martin.