Magnetically inserted neural electrodes: Immune response and functional lifetime
Abstract
Neural recording and stimulation have great potential for clinical applications, such as treating neurological conditions like Parkinson's disease or epilepsy, or for controlling prosthetic limbs. However, the feasibility of long-term neural recording is questionable because implantable electrodes eventually fail due to an immune response caused by the implantation and constant presence of the electrode. Astrocytes and microglia attempt to engulf the electrode increasing the electrical impedance between the electrode and neurons, and possibly pushing neurons away from the recording site. Faster insertion speed, finer tip geometry, smaller electrode size, and lower material stiffness all seem to decrease damage caused by insertion and reduce the intensity of the reactive tissue response. However, electrodes that are too small result in buckling during insertion. We propose that by magnetically inserting electrodes at high speeds, smaller (25 µm or less) electrodes can be implanted easily and improve the reliability of neural interfaces. To assess long-term functionality in terms of the foreign body response and ability to record from single units, 6 Long-Evans rats were implanted for 31 days with impedance measurements and neural recordings taken daily. Magnetically inserted electrodes showed the ability to resolve single unit activity throughout the duration of the study, while PlasticsOne electrodes lost all signal by day 17. PlasticsOne impedance increased up to 581.2 ± 190.8% increase on day 31 from day 0, while magnetically inserted electrode impedance saw no significant increase, with a 13.7 ± 91.8% impedance increase on day 31 from day 0. These findings suggest that these smaller (25 µm) magnetically inserted microwire electrodes reduce the reactive tissue response and allow longer functional lifetimes for neural interfaces.
Degree
M.S.B.M.E.
Advisors
Irazoqui, Purdue University.
Subject Area
Biomedical engineering
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