Weihua Pei

Dry electrode for the measurement of biopotential signals

This paper introduces a kind of silicon-based dry electrode for measuring biological signals. It uses microneedle arrays to penetrate into the stratum corneum to reduce skin impedance. The dry electrode requires neither skin preparation nor the electrolytic gel, is easy to use and causes no skin allergy. Two different technologies are chosen to manufacture microneedle arrays of dry electrode. One is deep dry etching combined with isotropic wet etching. The other is mechanical dicing combined with chemical wet etching (including isotropic wet etching and anisotropic wet etching). Microneedle arrays are coated with metal and divided into 25 mm2 as dry electrode patch. Impedance testing shows that the impedance value of dry electrode can be comparable with that of commercial electrode in the 20 Hz-10 kHz frequency range. The steady-state visual evoked potential recording and analysis prove that the dry electrode can be used to detect electroencephalography.

A fiber-based implantable multi-optrode array with contiguous optical and electrical sites.

OBJECTIVE Although various kinds of optrodes are designed to deliver light and sense electrophysiological responses, few have a tightly closed optical delivering site or electrical recording site. The large space between them often blurs the stimulation location and light intensity threshold. APPROACH Based on an optical fiber, we develop an optrode structure which has a coniform tip where the light exit point and gold-based electrode site are located. The optrode is fabricated by integrating a metal membrane electrode on the outside of a tapered fiber. Half of the cone-shape tip is covered by a layer of gold membrane to form the electrode. A commercial fiber connector, mechanical transfer (MT) module, is chosen to assemble the multi-optrode array (MOA). The MT connector acts as both the holder of the optrode array and an aligning part to connect the MOA with the light source. MAIN RESULTS We fabricated a pluggable MOA weighing only 0.2 g. The scanning electron microscope images showed a tight cover of the metal layer on the optrode tip with an exposure area of 1500 µm(2). The electrochemical impedance of the optrode at 1 kHz was 100 kΩ on average and the light emission intensity reached 13 mW. The optical modulating and electrophysiological recording ability of the MOA was validated by monitoring the response of cells in a ChR2-expressing mouses cerebral cortex. Neurons that maintained high cluster quality (signal-to-noise ratio = 5:1) and coherence in response to trains of 20 Hz stimulation were monitored. SIGNIFICANCE The optrode array reduces the distance between the optical stimulating sites and electrophysiological sites dramatically and can supply multiple channels to guide different lights simultaneously. This optrode with its novel structure may lead to a different kind of optical neural control prosthetic device, opening up a new option for neural modulation in the brain.

Fabrication of strongly adherent platinum black coatings on microelectrodes array

Platinum black coating can effectively improve the performance of MEAs (microelectrodes array) in neural signal transduction, though its lack of adhesion strength and durability tampers its usage in long term experiments. Here a new method of composite electrodeposition provides highly adhesive platinum black coating that enables MEAs for a month’s long task and repeatable utilization. The new method was compared with present techniques on multiple aspects, e.g. actual surface area, surface morphology, interfacial impedance, durability and real application tests. Results show that the new composite coating provides greatly improved durability without compromising its performances. Neural cells were cultured on these MEAs for 40 days in vitro and spontaneous action potentials with high signal/noise ratio were recorded. Theoretical model and simulation provided preliminary understanding on the mechanism of this strengthened platinum black coating.

A low-noise fully-differential CMOS preamplifier for neural recording applications

A fully-differential bandpass CMOS preamplifier for extracellular neural recording is presented in this paper. The capacitive-coupled and capacitive-feedback topology is adopted. We describe the main noise sources of the proposed preamplifier and discuss the methods for achieving the lowest input-referred noise. The preamplifier has a midband gain of 43 dB and a DC gain of 0. The −3 dB upper cut-off frequency of the preamplifier is 6.8 kHz. The lower cut-off frequency can be adjusted for amplifying the field or action potentials located in different bands. It has an input-referred noise of 3.36 μVrms integrated from 1 Hz to 6.8 kHz for recording the local field potentials (LFPs) and the mixed neural spikes with a power dissipation of 24.75 μW from 3.3 V supply. When the passband is configured as 100 Hz-6.8 kHz for only recording spikes, the noise is measured to be 3.01 μVrms. The 0.115 mm2 prototype chip is designed and fabricated in 0.35-μm N-well CMOS (complementary metal oxide semiconductor) 2P4M process.

Fabrication of Dry Electrode for Recording Bio-potentials

Development of minimally invasive dry electrodes for recording biopotentials is presented. The detailed fabrication process is outlined. A dry electrode is formed by a number of microneedles. The lengths of the microneedles are about 150?m and the diameters are about 50?m. The tips of the microneedles are sharp enough to penetrate into the skin. The silver/silver chloride is grown on microneedle arrays and demonstrates good character. The electrocardiogram shows that the dry electrode is suitable for recording biopotentials.

Swarm Intelligence-Inspired Spontaneous Fabrication of Optimal Interconnect at the Micro/Nanoscale

A spontaneous process is demonstrated to assemble nanoparticles into an optimal interconnect, as natural systems spontaneously figure out the shortest path. The optimal interconnect leads to a 65.9% decrease in electromagnetic interference, a 17.1% decrease in delay, and a 24.5% decrease in energy-delay. It will be of great significance for interconnect fabrication of versatile electronic circuits.

Design of Portable Multi-Channel EEG Signal Acquisition System

A portable multi-channel electroencephalography (EEG) signal acquisition system operated by battery is designed in this paper. EEG is a recording of the electrical activity of the brain from the scalp and the recorded waveforms provide insights into the dynamic aspects of brain activity. The amplifier with a bandwidth of 0.8-35Hz is designed by use of integrated circuits such as the low-power instrumentation amplifier AD623, low-power, high gain operational amplifiers TLC27L4, etc. The amplified EEG signals are digitized by an A/D (analog to digital) converter built-in MSP 430 MCU (micro-controller unit). The digitized signals are transmitted to a PC by a wired serial port or stored in the SD (secure digital) memory card. Experimental results show that the system could implement the acquisition and storage of the EEG signals efficiently. This system would be of benefit to all involved in the use of EEG for clinical diagnosis and monitoring, or even BCI (brain computer interface).

Effects of subretinal implant materials on the viability, apoptosis and barrier function of cultured RPE cells

BackgroundSubretinal microphotodiode array (MPDA) is a type of visual prosthesis used for the implantation in the subretinal space of patients with progressive photoreceptor cell loss. The present study aimed to evaluate the effect of materials for MPDA on the viability, apoptosis and barrier function of cultured pig retinal pigment epithelium (RPE) cells.MethodsPrimary culture of pig RPE cells was performed and 24 pig eyes were used to start RPE culture. The third passage of the cultures was plated on different materials for MPDA and MPDAs. The tetrazolium dye-reduction assay (MTT) was used to determine RPE cell viability. Flow cytometry was measured to indicate the apoptosis rates of RPE cells on different materials. RPE cells were also cultured on microporous filters, and the transepithelial resistance and permeability of the experimental molecule were measured to determine the barrier function.ResultsThe data from all the methods indicated no significant difference between the materials groups and the control group, and the materials tested showed good biocompatibility.ConclusionsThe materials for MPDA used in the present study had no direct toxicity to the RPE cells and did not release harmful soluble factors that affected the barrier function of RPE in vitro.

Efficacy and reliability of long-term implantation of multi-channel microelectrode arrays in the optical nerve sheath of rabbit eyes

In addition to epiretinal and subretinal areas, the optic nerve (ON) is also a candidate location for implanting visual prosthesis to restore vision of patients with retinitis pigmentosa (RP). Since the ON receives all the signals from the retina, stimulating the ON may potentially evoke phosphenes over a wider range of visual field. In this study, we designed a 9-channel microelectrode array and implanted it between the dura mater and pia mater of rabbit ONs by lateral orbitotomy. We recorded the current thresholds and evaluated the efficacy of the array using electrically evoked potentials (EEPs). Spatial discrimination of approximately 20° was verified by EEP maps over visual cortex. A large area of the visual field (over 130° along horizontal meridian) could be activated by this microelectrode array. Visual evoked potentials (VEPs) and different pathological examinations were used to examine potential damage of ONs. One year post implantation, we did not notice significant damages to either the ONs or the microelectrode arrays. EEPs were successfully recorded up to 6months post implantations. However, further studies are still needed to reduce fibrous encapsulation of the microelectrode array, which resulted in a gradual elevation of current thresholds to elicit EEPs.

Implantable CMOS neuro-stimulus chip for visual prosthesis

A prototype chip with 2×2 pixels for implanting in blind patients affected by outer retinal degeneration is presented in this paper. This visual prosthesis chip imitates the degenerated photoreceptor cells, senses the incident light and stimulates the remaining healthy layers of retina or optic nerve. Each pixel integrates photodiode and stimulus pulse generator, converting the illumination on the eyes into 3-bit resolution bi-phasic current pulses. On-chip charge cancellation modules are used to discharge each electrode site for tissue safety. The prototype chip is designed and fabricated in 0.18-μm N-well CMOS (complementary metal oxide semiconductor) 1P6M Mix-signal process, with a ±2.5 V dual voltage supply. The functionality of the fabricated chip is demonstrated on anesthetized rabbits. Neural responses in visual cortex are successfully evoked by the neuro-stimulus chip through an on-board trigger interface and flexible electrode.