Analyzing brain activity is crucial for diagnosing conditions like epilepsy and other mental health disorders. Among various methods, electroencephalography (EEG) is considered the least intrusive, using electrodes placed on the scalp to capture brain signals. However, the downside is that EEG has limited resolution, as brain signals get distorted and weakened by the time they reach the scalp. Electrocorticography (ECoG), on the other hand, places electrodes directly onto the brain's surface, offering much better recordings due to their proximity to the area of interest. These electrodes can also send electrical pulses to manage symptoms like epileptic seizures. But there's a hitch: conventional ECoG electrodes don't usually fit well with the brain's shape and mechanical properties, leading to issues like increased brain pressure. Although softer electrodes have been created to address this issue, they tend to lack durability or involve complex manufacturing steps. Now, researchers have designed flexible thin-film electrodes placed directly on brain tissue that align well with the brain's mechanical properties. This new design improves ECoG recordings and also allows for more targeted stimulation of neurons.

A research team at Tokyo Institute of Technology (Tokyo, Japan) has developed a novel flexible neural electrode made from a material known as polystyrene-block-polybutadiene-block-polystyrene (SBS). Using an inkjet printer, the team fabricated conductive wiring on the electrode with gold nanoink and then proceeded to cover the circuit by stacking another SBS layer as insulation, with laser-perforated microchannels as measurement or stimulation points. The team undertook extensive mechanical testing and simulations to show that these electrodes conform well to the brain's irregular shape. The straightforward design and manufacturing process also make these electrodes practical for broader applications.

To validate the effectiveness of their electrodes, the researchers conducted several tests on rat models with epilepsy. With their new ECoG electrodes, they were able to accurately gauge brain responses when the rats' whiskers were mechanically affected. Moreover, the electrodes were used to visualize seizure activities that were chemically induced. They were even able to trigger specific movements in the rats by sending electric pulses through particular channels on the electrode, indicating its potential for targeted brain stimulation. Notably, these electrodes did not result in any inflammation or negative effects in the rats' brains, even weeks after the tests. The team aims to refine this promising technology for future clinical use.

“As far as we know, this is the first study to demonstrate such ultra-conformable ECoG electrodes based on printed electronics, which closely match the mechanical properties of brain tissue,” said Associate Professor Toshinori Fujie of Tokyo Tech who led the team. “The integration of our thin-film electrode with an implantable device could make it even less invasive and more sensitive to the brain’s abnormal electrical activity. This would enable improved diagnostics and therapeutic strategies for the management of intractable epilepsy.” 

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