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Graphene is impervious to the harsh ionic solutions found in the human body. Moreover, graphene's ability to conduct electrical signals means it can interface with neurons and other cells that communicate by nerve impulse, or action potential. These features have made graphene a material of some promise in next-generation bionic technology. In November , Jose Garrido, a nanotechnologist at the Walter Schottky Institute in Munich, Germany, took a big bionic step when he showed that arrays of transistors made of graphene can detect action potentials in heart cells.
Apart from its stability and favourable electronic properties, graphene is also flexible, so it can be wrapped around delicate tissues. No other material shares all these features, Bergonzo says, adding that graphene opens up research opportunities in neural prosthetics. To make graphene transistors, Garrido uses a method called chemical vapour deposition see 'Beyond sticky tape', page S32 and grows a layer of cardiomyocytes directly on top of the array.
Like other electrogenic cells, cardiomyocytes use action potentials to pass electrical signals along from cell to cell. Each of those voltage spikes changes the local electrostatic environment by inducing a flow of ions in the channel in the electrolyte separating the cells and the transistors. Garrido's transistors respond to this ion current by altering their electrical resistance, explains James Hone, who specializes in nanoscale devices at Columbia University in New York.
The fluctuation in resistance constitutes a detectable signal between cardiomyocytes. Unlike silicon transistors, those made of graphene can't be switched off — its physical properties don't allow for that, Hone says — and this means they're not suited to digital applications where devices must be able to generate ones and zeroes see 'Back to analogue', page S What graphene transistors are good at, according to Garrido, is biological sensing — the sort of task that eyes and ears perform.
In such analogue applications, the ability to switch off is not critical, and graphene's distinct qualities come to the fore. Should silicon transistors be used in the human body, they would need to be coated with metal oxide to boost their stability in solution, Garrido says. Those layers trap ions that produce noisy interference and thus degrade signal quality. Graphene transistors, on the other hand, don't require an oxide coat so they generate less intrinsic noise, which enables them to detect the faint signals generally below a few hundred microvolts of cell communication.
Graphene is not the only carbon-based material with bionic potential. Diamond nanocrystals show promise in retinal implants to treat blindness, says Bergonzo.
But diamond is solid, inflexible and a poor conductor. Otherwise, you risk giving too much stimulation, or not enough. Serge Picaud, principal investigator with the Vision Institute in Paris, involved in the NeuroCare project, adds that because graphene is so thin, it could improve the interface between retinal implants and eye tissues.
And those closer connections, he says, could improve sight. Hone emphasizes that research into graphene-based bioelectronics is in its infancy. Scientists still face fundamental challenges in manufacturing, he says. Chemical vapour deposition, in particular, doesn't generate perfect graphene, and this limits the material's electronic performance see 'Beyond sticky tape', page S Moreover, materials scientist John Rogers at the University of Illinois in Urbana—Champaign cautions that silicon is still a contender.
Silicon can be fabricated into structures as thin as 10 nm; while that doesn't match the 1-nm dimensions possible with graphene, it might just work. What's more, Rogers points to a deep scientific and engineering base for silicon in the semiconductor industry. Rogers says that researchers are finding new ways to encapsulate implanted silicon devices so they don't harm tissue.
Still, Rogers sees tremendous opportunities for graphene in bioelectronic sensing because of the carbon material's much lower electrical noise. He envisages a hybrid approach that takes advantage of the strengths of both silicon and graphene. For his part, Garrido says he's now working to stack graphene transistor arrays on flexible substrates, such as the biocompatible polymers parylene and polyimide, each mechanically and heat stable.
Hess, L. Download references. Reprints and Permissions. Schmidt, C. Bioelectronics: The bionic material. Nature , S37 Download citation. Published : 14 March Issue Date : 15 March Frontiers in Neuroscience Advanced Materials Journal of Materials Chemistry C Biomaterials By submitting a comment you agree to abide by our Terms and Community Guidelines.
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Advanced search. Skip to main content. Register your interest. Subjects Biomedical materials Electronic properties and devices. Graphene could make an ideal basis for a medical repair kit. Download PDF. Cortical neurons being grown on graphene for use as biological implants nuclei are stained blue. Remaining challenges. References 1 Hess, L.
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Bioelectronics: The bionic material
Bioelectronics is a field of research in the convergence of biology and electronics. At the first C. Workshop, in Brussels in November , bioelectronics was defined as 'the use of biological materials and biological architectures for information processing systems and new devices'. Bioelectronics, specifically bio-molecular electronics, were described as 'the research and development of bio-inspired i. Department of Commerce, defined bioelectronics in a report as "the discipline resulting from the convergence of biology and electronics". A key aspect is the interface between biological materials and micro and nano-electronics.
Bioelectronics: The Bionic Material