Shape-transforming brain sensor adheres to curved surfaces for ultrasound neurostimulation

Focused transcranial ultrasound, a non-invasive technique for stimulating specific areas of the brain using high-frequency sound waves, could be a promising treatment strategy for many neurological disorders. Most notably, it could help treat drug-resistant epilepsy and other conditions associated with recurrent tremors.

Researchers from Sungkyunkwan University (SKKU), Institute of Basic Sciences (IBS) and Korea Institute of Science and Technology recently developed a new sensor that could be used to perform targeted transcranial ultrasound on patients . This sensor, presented in an article published in Natural electronicsadapts its shape and can adhere tightly to cortical surfaces, allowing users to record neural signals and stimulate specific brain regions via low-intensity ultrasound waves.

“Previous research on brain sensors that contact the surface of the brain have struggled to accurately measure brain signals due to the inability to closely conform to the complex folds of the brain,” said Donghee Son, supervising author of the study, at Tech Xplore.

“This limitation has made it difficult to accurately analyze the entire surface of the brain and accurately diagnose brain damage. While a brain sensor previously developed by Professor John A. Rogers and Professor Dae-Hyeong Kim has solved this problem to some extent due to its extremely thin shape, it still faced challenges in achieving tight adhesion in regions with significant curvature.

The sensor previously developed by Professors Rogers and Kim allows more precise measurements to be collected from the surface of the brain. Despite its promise, this sensor had various limitations, such as its inability to adhere to brain surfaces with greater curvature, as well as its tendency to slip from its original attachment point due to micro-movements in the brain and the flow of light. cerebrospinal fluid (CSF).

These observed challenges limit its potential use in medical settings, as they reduce its ability to consistently measure brain signals in target regions for prolonged periods. As part of their study, Son and his colleagues set out to develop a new sensor that could overcome these limitations, adhering well to the curved surfaces of the brain and thus allowing the reliable collection of measurements over extended periods of time.

“The new sensor we developed can fit tightly to highly curved brain regions and adhere firmly to brain tissue,” Son said. “This strong adhesion allows for precise, long-term measurement of brain signals from targeted areas.”

The sensor developed by Son and his colleagues, called ECoG, adheres securely to brain tissue without forming a vacuum. This can significantly reduce noise from external mechanical movements.

“This feature is particularly important for improving the effectiveness of epilepsy treatment with low-intensity focused ultrasound (LIFU),” Son said. “Although it is well known that ultrasound can help minimize seizure activity, variability in patient conditions and differences between individuals have posed significant challenges in tailoring treatments to each patient.”

In recent years, many research groups have attempted to design personalized ultrasound stimulation treatments for epilepsy and other neurological disorders. However, to tailor treatments to each patient’s needs, they should be able to measure the patient’s brain waves in real time while stimulating specific regions of the brain.

“Conventional sensors attached to the surface of the brain struggled to solve this problem because ultrasound-induced vibrations caused significant noise, making it difficult to monitor brain waves in real time,” Son said.

“This limitation posed a major barrier to creating personalized treatment strategies. Our sensor significantly reduces noise, enabling successful treatment of epilepsy through personalized ultrasound stimulation.”

The shape-transforming, cortex-adherent brain sensor developed by Son and colleagues includes three main layers. These include a hydrogel-based layer that can bond to tissue both physically and chemically, a self-healing polymer-based layer that can change shape to conform to the shape of the surface beneath, and an ultrathin, stretchable layer containing gold electrodes and interconnects.

“When the sensor is applied to the surface of the brain, the hydrogel layer undergoes a gelation process, initiating a powerful and instantaneous attachment to the brain tissue,” Son explained.

“Following this, the self-healing polymer substrate begins to deform, conforming to the curvature of the brain, thereby increasing the contact area between the sensor and tissue over time. Once the sensor has completely adhered to the contours of the brain, it is ready to work.”

The sensor developed by this research team has several advantages over other brain sensors introduced in recent years. First, it can attach securely to brain tissue while adapting its shape to fit perfectly on brain surfaces, regardless of their level of curvature.

By adapting to the shape of curved surfaces, the sensor minimizes vibrations produced by external ultrasound simulation. This could allow doctors to accurately measure waves in their patients’ brains, both under normal conditions and during an ultrasound simulation.

“We hope that this technology will not only be applicable to the treatment of epilepsy, but also to the diagnosis and treatment of various brain disorders,” Son said. “The most critical aspect of our work is the combination of tissue adhesive technology that allows the sensor to adhere firmly to the surface of brain tissue and shape transformation technology that allows it to conform to the contours of the brain without creating gaps.”

So far, the new sensor developed by Son and his colleagues has been tested on live, awake rodents. The results collected were very promising, as the team was able to accurately measure brain waves and control seizures in the animals.

The researchers eventually plan to scale the sensor, building on their design to create a high-density network. After passing clinical trials, this improved sensor could diagnose and treat epilepsy or other neurological disorders while potentially paving the way for more effective prosthetic technologies.

“Our brain sensor is currently equipped with 16 electrode channels, which presents an area for improvement in terms of high-resolution mapping of brain signals,” Son added.

“With this in mind, we plan to significantly increase the number of electrodes to enable more detailed, high-resolution analysis of brain signals. Additionally, we aim to develop a minimally invasive method to implant the brain sensor on the surface of the brain, with the ultimate goal of applying it to clinical research.

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