Neuroelectronic interfacing with cultured multielectrode arrays toward a cultured probe

Efficient and selective electrical stimulation and recording of neural activity in peripheral, spinal, or central pathways requires multielectrode arrays at micrometer scale. ¿Cultured probe¿ devices are being developed, i.e., cell-cultured planar multielectrode arrays (MEAs). They may enhance efficiency and selectivity because neural cells have been grown over and around each electrode site as electrode-specific local networks. If, after implantation, collateral sprouts branch from a motor fiber (ventral horn area) and if they can be guided and contacted to each ¿host¿ network, a very selective and efficient interface will result. Four basic aspects of the design and development of a cultured probe, coated with rat cortical or dorsal root ganglion neurons, are described. First, the importance of optimization of the cell-electrode contact is presented. It turns out that impedance spectroscopy, and detailed modeling of the electrode-cell interface, is a very helpful technique, which shows whether a cell is covering an electrode and how strong the sealing is. Second, the dielectrophoretic trapping method directs cells efficiently to desired spots on the substrate, and cells remain viable after the treatment. The number of cells trapped is dependent on the electric field parameters and the occurrence of a secondary force, a fluid flow (as a result of field-induced heating). It was found that the viability of trapped cortical cells was not influenced by the electric field. Third, cells must adhere to the surface of the substrate and form networks, which are locally confined, to one electrode site. For that, chemical modification of the substrate and electrode areas with various coatings, such as polyethyleneimine (PEI) and fluorocarbon monolayers promotes or inhibits adhesion of cells. Finally, it is shown how PEI patterning, by a stamping technique, successfully guides outgrowth of collaterals from a neonatal rat lumbar spinal cord explant, after six days in cultur

Estimation of permeability for magnetic flux leakage modelling

Non-destructive testing techniques are gen-erally used for the evaluation of material properties and the detection of defects in pipelines. Especially, the measure-ment of magnetic flux leakage (MFL) is one of the most used methods for in-service monitoring of corrosion in buried oil and gas pipelines. However, for the geometrical reconstruction of defects in a pipeline from measured signals (the inverse problem), the magnetic properties of the mate-rial need to be known accurately. Due to the pipe geometry and wall thickness measurement of the bulk properties is complicated. In particular, the permeability of ferromagnetic steels shows a non-linear and hysteretic behaviour. Current research is focussed on the measurement and simulation of the permeability of pipeline material. The magnetic properties of a small ferromagnetic test sample is first investigated using a transformer set up in order to find a correct fitting equation for the non-linear permeability as a function of the magnetic flux density. This equation is then used for model simulations of a MFL test set up. Refitting the parameters of the permeability equation to the perme-ability of the pipeline material in the MFL set up proved that flux leakage signals could be predicted accurately for sev-eral defects by model simulation

A three-step approach to practical training in measurement

Abstract − This paper reports on a training program in measurement for undergraduate students, in which emphasis is put on a critical attitude with respect to the whole measurement process. A thorough analysis of the measurement environment, the measurement devices and the signal processing are prerequisites for a correct interpretation of the measurement results. These skills are trained using a complete system built up in modules that can be studied separately. The student starts with the characterization of transducers, followed by studying the associated signal processing and finally evaluates the performance of the complete measurement system, all by hands-on experiments

Validation of soft multipin dry EEG electrodes

Background: Current developments towards multipin, dry electrodes in electroencephalography (EEG) are promising for applications in non-laboratory environments. Dry electrodes do not require the application of conductive gel, which mostly confines the use of gel EEG systems to the laboratory environment. Aim: The aim of the current study is to validate soft, multipin, dry EEG electrodes by comparing their performance to conventional gel EEG electrodes. Methods: 15 healthy volunteers performed three tasks, with the 32-channel gel EEG system and the 32-channel dry EEG system: the 40Hz Auditory Steady-State Response (ASSR), the checkerboard paradigm, and the eyes open/closed task. Within-subject analyses were performed to compare the signal quality in time, frequency and spatial domain. Results: The results showed strong similarities between the two systems in time and frequency domain, by strong correlations of the visual (ρ=0.89) and auditory evoked potential (ρ=0.81), and moderate to strong correlations for the alpha band during eyes closure (ρ=0.81-0.86) and the 40Hz-ASSR power (ρ=0.66-0.72), respectively. However, delta and theta band power was significantly increased, and the signal-to-noise ratio was significantly decreased for the dry EEG system. Topographical distributions were comparable for both systems. Application time of the dry EEG system was significantly decreased with 8min. Conclusion: It can be concluded that the soft, multipin dry EEG system can be used brain activity research with similar accuracy as conventional gel electrodes

Avoiding Internal Capsule Stimulation With a New Eight-Channel Steering Deep Brain Stimulation Lead

Objective: Novel deep brain stimulation (DBS) lead designs are currently entering the market, which are hypothesized to provide a way to steer the stimulation field away from neural populations responsible for side effects and towards populations responsible for beneficial effects. The objective of this study is to assess the performances of a new eight channel steering-DBS lead and compare this with a conventional cylindrical contact (CC) lead. Approach: The two leads were evaluated in a finite element electric field model combined with multicompartment neuron and axon models, representing the internal capsule (IC) fibers and subthalamic nucleus (STN) cells. We defined the optimal stimulation setting as the configuration that activated the highest percentage of STN cells, without activating any IC fibers. With this criterion, we compared monopolar stimulation using a single contact of the steering-DBS lead and CC lead, on three locations and four orientations of the lead. In addition, we performed a current steering test case by dividing the current over two contacts with the steering-DBS lead in its worst-case orientation. Main Results: In most cases, the steering-DBS lead is able to stimulate a significantly higher percentage of STN cells compared to the CC lead using single contact stimulation or using a two contact current steering protocol when there is approximately a 1 mm displacement of the CC lead. The results also show that correct placement and orientation of the lead in the target remains an important aspect in achieving the optimal stimulation outcome. Significance Currently, clinical trials are set up in Europe with a similar design as the steering-DBS lead. Our results illustrate the importance of the orientation of the new steering-DBS lead in avoiding side effects induced by stimulation of IC fibers. Therefore, in clinical trials sufficient attention should be paid to implanting the steering DBS-lead in the most effective orientation

A novel lead design enables selective deep brain stimulation of neural populations in the subthalamic region

Objective. The clinical effects of deep brain stimulation (DBS) of the subthalamic nucleus (STN-DBS) as a treatment for Parkinson's disease are sensitive to the location of the DBS lead within the STN. New high density (HD) lead designs have been created which are hypothesized to provide additional degrees of freedom in shaping the stimulating electric field. The objective of this study is to compare the performances of a new HD lead with a conventional cylindrical contact (CC) lead. Approach. A computational model, consisting of a finite element electric field model combined with multi-compartment neuron and axon models representing different neural populations in the subthalamic region, was used to evaluate the two leads. We compared ring-mode and steering-mode stimulation with the HD lead to single contact stimulation with the CC lead. These stimulation modes were tested for the lead: (1) positioned in the centroid of the STN, (2) shifted 1 mm towards the internal capsule (IC), and (3) shifted 2 mm towards the IC. Under these conditions, we quantified the number of STN neurons that were activated without activating IC fibers, which are known to cause side-effects. Main results. The modeling results show that the HD lead is able to mimic the stimulation effect of the CC lead. Additionally, in steering-mode stimulation there was a significant increase of activated STN neurons compared to the CC mode. Significance. From the model simulations we conclude that the HD lead in steering-mode with optimized stimulation parameter selection can stimulate more STN cells. Next, the clinical impact of the increased number of activated STN cells should be tested and balanced across the increased complexity of identifying the optimized stimulation parameter settings for the HD lead