Figuring out a way to allow electrodes to directly interface with neurons without harming them is one of the most pressing tasks facing neuroscientists today. The resolution of this dilemma could have far reaching implications for treating a number of neurological disorders such as Parkinson’s disease or restoring sensory functions for amputees or paralyzed patients. But so far the going has been slow due to the complexity and sensitivity of the human brain.
However, a team of researchers from Italy’s University of Trieste and the Cambridge Graphene Center recently made significant headway in this direction when it successfully demonstrated that untreated graphene can be used to interface with neurons without damaging their integrity.
"For the first time we interfaced graphene to neurons directly," said Professor Laura Ballerini of the University of Trieste in Italy in a press release. "We then tested the ability of neurons to generate electrical signals known to represent brain activities, and found that the neurons retained their neuronal signaling properties unaltered. This is the first functional study of neuronal synaptic activity using uncoated graphene based materials."
The team’s research, published in ACS Nano, details how it used rat brain cell cultures to discover that untreated graphene electrodes interfaced perfectly with neurons. Other groups had previously shown how treated graphene (graphene typically coated in peptides, amino acid chains that “favor neuronal cohesion”) could be used to interact with neurons, although this produced a relatively low signal to noise ratio when compared with untreated graphene.
Graphene, a honeycomb lattice made of carbon atoms that can be 100 times stronger than steel, has a number of advantageous properties when compared with other materials that are frequently used to make electrodes for brain implants, such as silicon and tungsten. Electrodes made from these latter materials often suffer from a partial or total loss of signal over time due to the formation of scar tissue from the electrode insertion. This scar tissue partially or completely blocks the electric impulses which are normally able propagate without problems through gray matter, so the trick is figuring out how to implant an electrode without damaging neurons and thereby triggering the build up of scar tissue around the electrode.
Enter graphene, which has excellent conductivity, plasticity, and bioconductivity in the body, making it the ideal material for manufacturing electrodes which could be implanted without promoting the buildup of scar tissue.
As the team details in its report, it used electron microscopy and immunofluorescence to study how the graphene interacted with neuron cultures and found that the neurons remained healthy and capable of transmitting electrical signals normally without any adverse reactions which would lead to the formation of scar tissue.
"Hopefully this will pave the way for better deep brain implants to both harness and control the brain."
"We are currently involved in frontline research in graphene technology towards biomedical applications," said Professor Maurizio Prato from the University of Trieste. "In this scenario, the development and translation in neurology of graphene-based high-performance biodevices requires the exploration of the interactions between graphene nano- and micro-sheets with the sophisticated signaling machinery of nerve cells. Our work is only a first step in that direction."
The graphene electrodes imagined by the team could have far reaching implications for treating a number of neurological disorders, ranging from Parkinson’s disease to sensory restoration for amputees or paralyzed patients. Our understanding of the brain is such that we now know how to manipulate electrical impulses to control a robotic arm, or interfere with electrical signals to treat motor disorders (such as Parkinson’s or epilepsy). The dilemma is in trying to figure out a way to successfully integrate electrodes capable of manipulating these electric impulses in the desired manner without harming brain tissue in the process, which is exactly what makes Cambridge-Trieste team’s success with graphene such a big deal.
Although Prato calls it “only a first step” in that direction, it is a very significant first step. Now that the team has had an initial success with pristine graphene neuro-interfaces, it hopes to conduct more research with different forms of graphene, such as multi-layer or monolayer, to see how altering graphene’s material properties affects neural connections.
"These initial results show how we are just scratching the tip of an iceberg when it comes to the potential of graphene and related materials in bio-applications and medicine," said Professor Andrea Ferrari, Director of the Cambridge Graphene Centre. This sentiment was echoed by Ballerini, who optimistically added, “Hopefully this will pave the way for better deep brain implants to both harness and control the brain, with higher sensitivity and fewer unwanted side effects."