Polypyrrole Coatings as Possible Solutions for Sensing and Stimulation in Bioelectronic Medicines

Abstract

Bioelectronic medicines record biological signals and provide electrical stimulation for the treatment of diseases. Advanced bioelectronic therapies require the development of electrodes that match the softness of the implanted tissues, as the present metal electrodes do not meet this condition. The objective of the present work was to investigate whether the electroconductive polymer polypyrrole (PPy) could be used for fabricating such electrodes, as PPy is several orders softer than metals. For this purpose, we here investigated if electrodes made using coatings and films of PPy doped with naphthalin-2-sulfonic acid (PPy/N) are capable to record and elicit by stimulation cardiac monophasic action potentials (MAPs) and if PPy/N is also biocompatible. The results of this study showed that the tested PPy/N electrodes are capable of recording MAPs almost identical to the MAPs recorded with platinum electrodes and eliciting stimulation-evoked MAPs almost identical to the spontaneous MAPs. In addition, we show here that the cell cultures that we used for biocompatibility tests grew in a similar manner on PPy/N and platinum substrates. We, therefore, conclude that PPy/N coatings and films have recording and electrical stimulation capabilities that are similar to those of platinum electrodes and that PPy/N substrates are as biocompatible as the platinum substrates.

Keywords: action potentials; bioelectronic medicine; polypyrrole; recording; stimulation.

Figure 1

Electron microscopy images of uncoated (a,b) and PPy/N coated nylon filaments (c–f), and of the PPy/N strips (g,h) that were used to fabricate the recording and stimulation electrodes, respectively.

Figure 2

The experimental setup used to simultaneously record monophasic action potentials (MAPs) from the surface of chick embryo ventricles and to induce by electrical stimulation evoked MAPs.

Figure 3

Monophasic action potentials (MAPs) simultaneously recorded from the surface of chick embryo ventricles using PPy/N and Pt electrodes (a), and MAPs evoked by electrical stimulation using PPy/N electrodes (b). Note: Similar as in Knollmann et al. [26], the morphological difference between the spike-and-dome MAPs from (a) vs. the low-plateau MAPs from (b) is due to the diameter difference between the electrodes used to record those MAPs, i.e., 300/450 vs. 200/280 µm bare/insulated in (a) and (b), respectively.

Figure 4

Duration and amplitude parameters of spontaneous MAPs recorded simultaneously with Pt and PPy/N electrodes from the ventricle of 9 chick embryos (a,b), and spontaneous MAPs vs. MAPs evoked by electrical in the ventricle of 9 chick embryos (c,d).

Figure 5

Fibroblasts proliferation on substrates covered with Pt and PPy/N. (a,b): fluorescence images of fibroblasts grown on Pt and PPy/N substrates, respectively; (c–f): SEM micrographs of fibroblasts grown on Pt and PPy?n substrates, respectively; (g): density of the fibroblasts grown on Pt and PPy/N substrates.