silicon and iridium-oxide

We developed and validated silicon-based neural probes for neural stimulating and recording in long-term implantation in the brain. The probes combine the deep reactive ion etching process and mechanical shaping of their tip region, yielding a mechanically sturdy shank with a sharpened tip to reduce insertion force into the brain and spinal cord, particularly, with multiple shanks in the same array. The arrays' insertion forces have been quantified in vitro. Five consecutive chronically-implanted devices were fully functional from 3 to 18 months. The microelectrode sites were electroplated with iridium oxide, and the charge injection capacity measurements were performed both in vitro and after implantation in the adult feline brain. The functionality of the chronic array was validated by stimulating in the cochlear nucleus and recording the evoked neuronal activity in the central nucleus of the inferior colliculus. The arrays' recording quality has also been quantified in vivo with neuronal spike activity recorded up to 566 days after implantation. Histopathology evaluation of neurons and astrocytes using immunohistochemical stains indicated minimal alterations of tissue architecture after chronic implantation.

Topics: Action Potentials; Animals; Cats; Cerebral Cortex; Cochlear Nucleus; Deep Brain Stimulation; Electrodes, Implanted; Electroencephalography; Immunohistochemistry; Iridium; Microelectrodes; Rabbits; Reproducibility of Results; Silicon; Time Factors

Several variations of microelectrode arrays are used to record and stimulate intracortical neuronal activity. Bypassing the immune response to maintain a stable recording interface remains a challenge. Companies and researchers are continuously altering the material compositions and geometries of the arrays in order to discover a combination that allows for a chronic and stable electrode-tissue interface. From this interface, they wish to obtain consistent quality recordings and a stable, low impedance pathway for charge injection over extended periods of time. Despite numerous efforts, no microelectrode array design has managed to evade the host immune response and remain fully functional. This study is an initial effort comparing several microelectrode arrays with fundamentally different configurations for use in an implantable epilepsy prosthesis. Specifically, NeuroNexus (Michigan) probes, Cyberkinetics (Utah) Silicon and Iridium Oxide arrays, ceramic-based thin-film microelectrode arrays (Drexel), and Tucker-Davis Technologies (TDT) microwire arrays are evaluated over a 31-day period in an animal model. Microelectrodes are compared in implanted rats through impedance, charge capacity, signal-to-noise ratio, recording stability, and elicited immune response. Results suggest significant variability within and between microelectrode types with no clear superior array. Some applications for the microelectrode arrays are suggested based on data collected throughout the longitudinal study. Additionally, specific limitations of assaying biological phenomena and comparing fundamentally different microelectrode arrays in a highly variable system are discussed with suggestions on how to improve the reliability of observed results and steps needed to develop a more standardized microelectrode design.

Topics: Action Potentials; Animals; Artifacts; Brain; Brain Injuries; Ceramics; Electric Impedance; Electrodes, Implanted; Electronics, Medical; Electrophysiology; Foreign-Body Reaction; Iridium; Microelectrodes; Neurons; Neurophysiology; Prosthesis Implantation; Rats; Rats, Long-Evans; Signal Processing, Computer-Assisted; Silicon; Time; Time Factors

We have developed a silicon-based neural microelectrode system for long-term neural recording and stimulation. Our aim is to design robust silicon-based microelectrode arrays that are suitable for implantation into various targets in the brain and spinal cord. The microelectrode sites were electroplated with iridium oxide, thereby reducing the AC impedance and increasing charge storage capacity, compared to gold electrodes. To date, the implanted probe system has been able to record resolvable single-unit action potentials for five months in the ventral cochlear nucleus of the cats' brainstem.

Topics: Animals; Brain; Brain Stem; Cats; Electric Impedance; Electric Stimulation; Electrochemistry; Electrodes, Implanted; Iridium; Microelectrodes; Nervous System Physiological Phenomena; Neurons; Signal Transduction; Silicon; Spinal Cord