Flexural bending to approximate cortical forces exerted by electrocorticography (ECoG) arrays

Area of Science:

• Biomedical Engineering
• Materials Science
• Neuroscience

Background:

• Electrocorticography (ECoG) arrays exert force on the brain due to their bending to match cranial curvature.
• This mechanical force can adversely affect both short-term and long-term patient outcomes.
• Reducing this force is crucial for improving the clinical utility of ECoG devices.

Purpose of the Study:

• To mechanically characterize a novel liquid crystal polymer (LCP) ECoG array prototype.
• To demonstrate that a thinner ECoG array geometry reduces the force exerted on the brain's cortex.
• To establish flexural testing as a necessary method for assessing ECoG array forces.

Main Methods:

• Developed a low-force flexural testing machine to measure bending forces of ECoG arrays.
• Calculated effective flexural moduli and approximated maximum forces exerted on the brain.
• Utilized a four-point flexure testing procedure to quantify forces.

Main Results:

• The LCP ECoG prototype exhibited a maximal force less than 20% of tested commercial arrays.
• Despite LCP being 24x more rigid than silicone, the prototype's reduced force was attributed to its 2.9x-3.25x thinner profile.
• Material properties like elastic modulus are insufficient for predicting ECoG flexural behavior due to scale dependency and anisotropy.

Conclusions:

• Flexible circuit manufacturing techniques, specifically reducing ECoG array thickness, can significantly lower forces exerted on the brain.
• Flexural testing is essential for accurately assessing ECoG array forces, as material properties are scale-dependent.
• This experimental method enables the design of ECoG arrays that minimize brain force, potentially enhancing clinical utility.