Rapid evaluation of the durability of cortical neural implants using accelerated aging with reactive oxygen species

Abstract

Objective-A challenge for implementing high bandwidth cortical brain-machine interface devices in patients is the limited functional lifespan of implanted recording electrodes. Development of implant technology currently requires extensive non-clinical testing to demonstrate device performance. However, testing the durability of the implants in vivo is timeconsuming and expensive. Validated in vitro methodologies may reduce the need for extensive testing in animal models.Approach-Here we describe an in vitro platform for rapid evaluation of implant stability. We designed a reactive accelerated aging (RAA) protocol that employs elevated temperature and reactive oxygen species (ROS) to create a harsh aging environment. Commercially available microelectrode arrays (MEAs) were placed in a solution of hydrogen peroxide at 87 °C for a period of 7 days. We monitored changes to the implants with scanning electron microscopy and broad spectrum electrochemical impedance spectroscopy (1 Hz-1 MHz) and correlated the physical changes with impedance data to identify markers associated with implant failure.Main results-RAA produced a diverse range of effects on the structural integrity and electrochemical properties of electrodes. Temperature and ROS appeared to have different effects on structural elements, with increased temperature causing insulation loss from the electrode microwires, and ROS concentration correlating with tungsten metal dissolution. All array types experienced impedance declines, consistent with published literature showing chronic (>30 days) declines in array impedance in vivo. Impedance change was greatest at frequencies <10 Hz, and smallest at frequencies 1 kHz and above. Though electrode performance is traditionally characterized by impedance at 1 kHz, our results indicate that an impedance change at 1 kHz is not a reliable predictive marker of implant degradation or failure.Significance-ROS, which are known to be present in vivo, can create structural damage and change electrical properties of MEAs. Broad-spectrum electrical impedance spectroscopy

Recent advances in neural electrode–tissue interfaces

“…This correlates with in vivo findings, where tungsten wires exhibit the greatest degree of degeneration immediately after implantation, likely due to the increased free radical concentration and comparatively harsh environment around the implant post-surgery [4]. In addition to tungsten, reactive oxygen species showed corrosive effects on Pt/Ir, Pt, Ir, Au, Silicon Nitride, Polyimide, and Parylene-C [43]. Depending on the type of degrading material, degradation products may worsen the inflammation.…”

“…These species may not only damage the tissue, but also accelerate the degradation of the electrode materials. In an in vitro study, tungsten electrodes exhibit a heightened degree of corrosion when exposed to common reactive oxygen species and H 2 O 2 [42, 43]. This correlates with in vivo findings, where tungsten wires exhibit the greatest degree of degeneration immediately after implantation, likely due to the increased free radical concentration and comparatively harsh environment around the implant post-surgery [4].…”

Graphitic Carbon Electrodes on Flexible Substrate for Neural Applications Entirely Fabricated Using Infrared Nanosecond Laser Technology

“…The devices were left in solution for one week, at constant temperature of 37 °C and protected from UV light. The presence of H 2 O 2 is intended to simulate the in vivo environment surrounding the electrodes during the acute post-surgery tissue response to the implant, where reactive oxygen species (ROS) are released by the brain immune cells to attack the foreign body for the first 7 days after the implantation 30 . After one week, electrochemical impedance spectroscopy (EIS) measurements were taken to determine whether the devices remained functional.…”

Resorbierbare Implantate in der Unfallchirurgie

“…Zurzeit werden Implantate oder Füllungen aus Biomaterialien vorwiegend im Bereich der Zahn-, Herz-, Gehirn-oder Knochenchirurgie appliziert [7][8][9]. Diese sind nicht notwendigerweise resorbierbar.…”