Implantable devices for use in the body of a subject, such as neural prosthetic systems, have had limited success due to the challenges presented by the environment the devices are exposed to.
Long-term interaction with the implantable device and the body takes a toll on these implantable devices. Impedance degradation, scar tissue formation, and inflammation around the implant area can have deleterious effects on the functioning of implanted devices. Building robust and scalable long-term implants could advance the understanding of brain networks related to network disorders. Therefore, it is desirable to develop long-lasting, high performance implantable devices.
The Litt Lab has developed a bio-inert graphene coating for biological sensors and stimulation applications. The method encapsulates electrode materials so that normal tissue reactions with the substrate, such as immunoreactivity, are dramatically reduced, as only the graphene interacts with tissues. Single layer graphene reduces the electrical impedance and improves the charge injection capacity, thus reducing noise. The improved signal to noise ratio has been confirmed by tests of graphene/metal bilayer electrodes fabricated on a Si substrate evaluated on a mouse brain and a rat hippocampal slice.
The electrode contains a bi-component conductor comprising a metal layer and a graphene passivation layer. As a passivation layer, graphene may block chemical reactions between the underlying metal and body tissues. This allows for the use of metals more efficient in charge transfer which may increase device battery life and lower the cost of current implantable devices. Additionally, graphene has potential to decrease tissue damage over metals currently used for electrodes, thus allowing probes to remain implanted for longer times than is currently practiced.
- The metal electrodes have a graphene passivation layer that prevents corrosion and chemical reactions with the underlying layers and the surrounding environment. As a passivation layer, the graphene may block chemical reactions between the underlying metal and body tissues.
- Graphene has low impedance and a high charge injection capacity that may allow scaling to single-cell levels. Graphene monolayers have a thickness of about 0.34nm, therefore adding minimal thickness to the electrode.
- The graphene passivation layer also prevents diffusion of gas molecules, thus preventing metal corrosion and potential longer implantation times.
- Highly sensitive
Graphene-passivated implantable electrodes
Stage of Development:
- Tested on mouse and rat brain slices
- Future work involves in vivo animal testing to evaluate the efficacy and safety of these graphene coated electrodes
PCT application filed Jan. 6, 2015 PCT/US2015/010224 pending