Bioelectrodes designed to match a person’s brain surface may help advance neural interfaces for neurodegenerative disease monitoring and treatment, according to a study led by Penn State researchers.
These sensors are usually made from stiff materials in a one-size-fits-all design that struggles to match the brain’s complex structure. The researchers said they have created a novel approach to 3D printing bioelectrodes that can stretch and morph to fit the minor differences that make every brain unique. Their work is detailed in Advanced Materials.
The team used software to simulate detailed brains based on MRI scans taken from 21 human patients, shaping a set of electrodes tailored for brains’ specific structures before 3D printing the electrodes and models of the brains.
In their paper, the team reported that their electrodes better fit the structure of the brain than traditional designs, while remaining effective and biologically compatible, as seen in tests with rats.
The folds in the human brain are created through gyrification, where the cortical sheet on the outer wall of the brain bunches up into ridges called gyri and grooves called sulci. This helps cells across the brain communicate at high speeds and allows for a relatively large organ to fit compactly in the skull.
Although the major cortical folds are consistent across individuals, the precise layout of the brain’s gryi and sulci changes from person to person, according to corresponding author Tao Zhou, Wormley Family Early Career Professor and assistant professor of engineering science and mechanics at Penn State University.
“Each person has a different brain structure, depending on their height, weight, age, sex and more,” said Zhou. “Despite this, we try to fit neural interfaces onto brains like they have identical structures. This motivated us to create electrodes that are tailored for each individual.”
The electrodes are built mainly from a hydrogel to better match with the soft tissues and patient-specific geometry of a brain. Furthermore, the team used a novel honeycomb-inspired structure that offers flexibility and strength, while remaining cost-effective and quick to print, said Zhou.
“The honeycomb structure helps us significantly reduce the stiffness of the electrodes, without sacrificing their mechanical strength,” Zhou said in a statement. “What’s more, the structure helps us reduce the overall material used during fabrication, reducing production time, cost and environmental impact.”
Production starts by taking an MRI scan of a patient's brain. This analysis is then rendered as a 3D model of the patient's brain, where the team uses computer software to tailor a bioelectrode specifically morphed to fit the ridges and grooves of the cerebral cortex.
After shaping, the team 3D printed the hydrogel electrode using direct ink printing, a technique that can create electrodes capable of monitoring and transmitting brain signals over a relatively small surface.
For this study, the team 3D printed models of 21 different participant brains, applying their electrodes and physically measuring how accurately the electrodes could fit the brain surface.
Compared to traditional approaches, the hydrogel-based electrodes follow the structure of the brain more precisely. Zhou said their approach produces electrodes that exhibit nearly perfect connectivity to electrical signals present in the brain. Additionally, its high malleability allows the gel to be applied to delicate brain tissue without causing damage.
According to Zhou, the softness of their electrodes enables closer and more stable contact with the brain, which facilitates higher-quality, more reliable monitoring. Moreover, bioelectrodes made with this approach do not impact fluid transport around the brain.
To further study their electrodes, the team placed them onto the brains of rats over 28 days. The rats did not exhibit any immune response to the printed electrodes, a key consideration in biodevice development, said Zhou. Additionally, the electrodes did not exhibit performance degradation, while offering sensitive and accurate readings of the electric and physiological signals in the brain.
source: Custom 3D-Printed Bioelectrodes Improve Neural Fit - The Engineer
