Simulating the Use of Discontinuous Patterned Hydrogel to Improve Inter‐Electrode Resistance on Electrode Arrays

BACKGROUND: A novel form of sensory stimulation aiming to treat spasticity has been developed, and a clinical trial is currently underway. This uses an electrode array controlled by a programmable 64-channel stimulator to spatially vary the electrical stimulation over time. However, when a continuous layer of hydrogel interfaces between the array and skin, stimulation spreads, causing lower current densities applied over larger areas of tissue. A new approach was developed, modeled, and tested, utilizing discontinuous patterned hydrogel to improve inter-electrode resistance on electrode arrays. METHODS: Finite-difference modeling was used to estimate stimulation distribution within the hydrogel and subcutaneous tissue under the electrode array. Repeated simulations modeled changes due to variations in hydrogel, skin, and subcutaneous tissue resistivity. Properties of both continuous sheets and patterned hydrogel were used for the simulation. Physical prototypes of the continuous and patterned hydrogel were manufactured and tested for comparison with the simulation. RESULTS: Simulation results showed a reduced spread of stimulation between electrodes when using the discontinuous patterned hydrogel compared to the continuous hydrogel. This was demonstrated consistently for all variations in hydrogel, skin, and subcutaneous tissue resistivity. Laboratory testing supported the simulation results and suggested the improved performance of the patterned hydrogel, compared with the continuous hydrogel, may become more substantial over time. CONCLUSIONS: While the simulation only approximates the stimulation distribution on electrode arrays, the results do show potential benefits of utilizing discontinuous patterned hydrogel to increase inter-electrode resistance. Laboratory testing and initial feedback from the clinical trial support the results indicated in the simulations.