Comparative mechanical analysis of deep brain stimulation electrodes.

The new field of neuro-prosthetics focuses on the design and implementation of neural prostheses to restore some of the lost neural functions. The electrode-tissue contacts remain one of the major obstacles of neural prostheses microstructure. Recently, Microelectrode fabrication techniques have been developed to have a long-term and stable interface with the brain. In this paper, a comparative analysis of finite element models (FEM) for several electrode layouts is conducted. FEM involves parametric and sensitivity analysis to show the effects of the different design parameters on the electrode mechanical performance. These parameters include electrode dimensions, geometry, and materials. The electrodes mechanical performance is evaluated with various analysis techniques including: linear buckling analysis, stationary analysis with axial and shear loading, and failure analysis for brittle and ductile materials. Finally, a novel figure of merit (FOM) is presented and dedicated to the various electrodes prototypes. The proposed designs take into account mechanical performance, fabrication cost, and cross sectional area of the electrode. The FOM provides important design insights to help the electrodes designers to select the best electrode design parameters that meet their design constraints.

3-D flexible nano-textured high-density microelectrode arrays for high-performance neuro-monitoring and neuro-stimulation.

We introduce a new 3-D flexible microelectrode array for high performance electrographic neural signal recording and stimulation. The microelectrode architecture maximizes the number of channels on each shank and minimizes its footprint. The electrode was implemented on flexible polyimide substrate using microfabrication and thin-film processing. The electrode has a planar layout and comprises multiple shanks. Each shank is three mm in length and carries six gold pads representing the neuro-interfacing channels. The channels are used in recording important precursors with potential clinical relevance and consequent electrical stimulation to perturb the clinical condition. The polyimide structure satisfied the mechanical characteristics required for the proper electrode implantation and operation. Pad postprocessing technique was developed to improve the electrode electrical performance. The planar electrodes were used for creating 3-D "Waterloo Array" microelectrode with controlled gaps using custom designed stackers. Electrode characterization and benchmarking against commercial equivalents demonstrated the superiority of the Flex electrodes. The Flex and commercial electrodes were associated with low-power implantable responsive neuro-stimulation system. The electrodes performance in recording and stimulation application was quantified through in vitro and in vivo acute and chronic experiments on human brain slices and freely-moving rodents. The Flex electrodes exhibited remarkable drop in the electric impedance (100 times at 100 Hz), improved electrode-electrolyte interface noise (dropped by four times) and higher signal-to-noise ratio (3.3 times).

High-density intracortical microelectrode arrays with multiple metallization layers for fine-resolution neuromonitoring and neurostimulation.

Intracortical microelectrodes play a prominent role in the operation of neural interfacing systems. They provide an interface for recording neural activities and modulating their behavior through electric stimulation. The performance of such systems is thus directly meliorated by advances in electrode technology. We present a new architecture for intracortical electrodes designed to increase the number of recording/stimulation channels for a given set of shank dimensions. The architecture was implemented on silicon using microfabrication process and fabricated 3-mm-long electrode shanks with six relatively large (110 µm ×110 µm) pads in each shank for electrographic signal recording to detect important precursors with potential clinical relevance and electrical stimulation to correct neural behavior with low-power dissipation in an implantable device. Moreover, an electrode mechanical design was developed to increase its stiffness and reduce shank deflection to improve spatial accuracy during an electrode implantation. Furthermore, the pads were post-processed using pulsated low current electroplating and reduced their impedances by ≈ 30 times compared to the traditionally fabricated pads. The paper also presents microfabrication process, electrodes characterization, comparison to the commercial equivalents, and in vitro and in vivo validations.

Massively-parallel neuromonitoring and neurostimulation rodent headset with nanotextured flexible microelectrodes.

We present a compact wireless headset for simultaneous multi-site neuromonitoring and neurostimulation in the rodent brain. The system comprises flexible-shaft microelectrodes, neural amplifiers, neurostimulators, a digital time-division multiplexer (TDM), a micro-controller and a ZigBee wireless transceiver. The system is built by parallelizing up to four 0.35 µm CMOS integrated circuits (each having 256 neural amplifiers and 64 neurostimulators) to provide a total maximum of 1024 neural amplifiers and 256 neurostimulators. Each bipolar neural amplifier features 54 dB-72 dB adjustable gain, 1 Hz-5 kHz adjustable bandwidth with an input-referred noise of 7.99 µVrms and dissipates 12.9 µW. Each current-mode bipolar neurostimulator generates programmable arbitrary-waveform biphasic current in the range of 20-250 µA and dissipates 2.6 µW in the stand-by mode. Reconfigurability is provided by stacking a set of dedicated mini-PCBs that share a common signaling bus within as small as 22 × 30 × 15 mm³ volume. The system features flexible polyimide-based microelectrode array design that is not brittle and increases pad packing density. Pad nanotexturing by electrodeposition reduces the electrode-tissue interface impedance from an average of 2 MΩ to 30 kΩ at 100 Hz. The rodent headset and the microelectrode array have been experimentally validated in vivo in freely moving rats for two months. We demonstrate 92.8 percent seizure rate reduction by responsive neurostimulation in an acute epilepsy rat model.

Finite difference time domain (FDTD) modeling of implanted deep brain stimulation electrodes and brain tissue.

This paper demonstrates the electromagnetic modeling and simulation of an implanted Medtronic deep brain stimulation (DBS) electrode using finite difference time domain (FDTD). The model is developed using Empire XCcel and represents the electrode surrounded with brain tissue assuming homogenous and isotropic medium. The model is created to study the parameters influencing the electric field distribution within the tissue in order to provide reference and benchmarking data for DBS and intra-cortical electrode development.

Real-time automated neural-network sleep classifier using single channel EEG recording for detection of narcolepsy episodes.

Conventional sleep staging and classification methods involve complicated settings to acquire multiple electrophysiological signals for extended recording durations, followed by specialists' analysis which is a time consuming exercise. These procedures need to be carried out in sleep clinics and are not suitable for applications based on real-time sleep monitoring and analysis. In this paper, a real-time sleep staging and classification technique is proposed using single EEG channel based on an artificial neural network classifier. This method is optimized to run on portable processing platforms with limited processing capabilities.

Design optimization methodology for dry EEG spikes array electrode.

Monitoring bio-electric events is a vital practice which provides medical data required in many clinical and research applications. Improving the performance of portable and ambulatory recording devices requires developing stable biomedical electrodes suitable for long term recording. This paper introduces an optimization design methodology to improve the electrical performance of dry electrodes used in electroencephalography through optimizing the geometrical design while abiding by design constraints which guarantee biocompatibility and mechanical stability.