The design of neural electrodes has changed in the past
decade,
driven mainly by the development of new materials that open the possibility
of manufacturing electrodes with adaptable mechanical properties and
promising electrical properties. In this paper, we report on the mechanical
and electrochemical properties of a polydimethylsiloxane (PDMS)
composite with edge-functionalized graphene (EFG) and demonstrate
its potential for use in neural implants with the fabrication of a
novel neural cuff electrode. We have shown that a 200 μm thick
1:1 EFG/PDMS composite film has a stretchability of up to 20%, a Young’s
modulus of 2.52 MPa, and a lifetime of more than 10000 mechanical
cycles, making it highly suitable for interfacing with soft tissue.
Electrochemical characterization of the EFG/PDMS composite film showed
that the capacitance of the composite increased up to 35 times after
electrochemical reduction, widening the electrochemical water window
and remaining stable after soaking for 5 weeks in phosphate buffered
saline. The electrochemically activated EFG/PDMS electrode had a 3
times increase in the charge injection capacity, which is more than
double that of a commercial platinum-based neural cuff. Electrochemical
and spectrochemical investigations supported the conclusion that this
effect originated from the stable chemisorption of hydrogen on the
graphene surface. The biocompatibility of the composite was confirmed
with an in vitro cell culture study using mouse spinal
cord cells. Finally, the potential of the EFG/PDMS composite was demonstrated
with the fabrication of a novel neural cuff electrode, whose double-layered
and open structured design increased the cuff stretchability up to
140%, well beyond that required for an operational neural cuff. In
addition, the cuff design offers better integration with neural tissue
and simpler nerve fiber installation and locking.