Combining biocompatible, flexible, conducting polymers with hydrogels is highly attractive for future biomedical devices. The fabrication of such devices, however, is not an easy task. Printing methods for making micropatterns of conducting polymers have, to date, focused on processes that require a drying step, but this means that they are incompatible with moist, hydrogel substrates.

Now, motivated by the possibility of exploiting the electronic properties of conducting polymers to make implanted electronic devices or in vitro cell culture materials, Matsuhiko Nishizawa and colleagues at Tohoku University in Japan1 have shown how micropatterns of the polymer known as PEDOT can be made on the surface of an agarose hydrogel to afford an organic, moist and flexible electrode.

To researchers poured a melted solution of agarose onto a master template of platinum electrodes and allowed the agarose to form a gel. The resulting agarose-covered platinum electrodes, in a gel about 2 mm thick, were then immersed in a monomer solution. Electropolymerization then gave a PEDOT–agarose film that had a PEDOT micropattern mirroring that of the platinum electrodes.

Fig. 1: Photograph of the PEDOT microelectrode array on a collagen sheet.

The PEDOT–agarose electrode could not be simply peeled off the master template because doing so caused the soft hydrogel to collapse. Instead, the researchers repeatedly oxidized and reduced the polymer, causing its volume to change, until the hybrid film detached from the substrate. The method is versatile and can be used to make micropatterns of PEDOT on other hydrogels, including collagen (Fig. 1) and fibrin.

Nishizawa and his colleagues then demonstrated that the PEDOT–agarose electrode could be used for electrical stimulation of the contractile fibers that make up muscle tissue (myotubes). A film of contractile myotubes within a fibrin matrix was laid on top of the electrode and stimulated with periodic voltage pulses. The electrode induced contraction of the myotubes, and the electrode itself was observed to contract in unison with the myotubes.

“These conducting polymer–hydrogel electrodes are safe, flexible, contractile and permeable,” says Nishizawa. “Their permeability for oxygen and nutrition would be a great advantage if used as implants. One possible application is therefore as an implanted electrode for recording and controlling the functions of muscle and neuronal tissues, including brain tissue.”