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Biomedical subjects

W L Rutten

Publications and source records attributed to W L Rutten.

At least 19 recordsLinked to original sources
PubMed2001

Viability of dielectrophoretically trapped neural cortical cells in culture.

Negative dielectrophoretic trapping of neural cells is an efficient way to position neural cells on the electrode sites of planar micro-electrode arrays. The preservation of viability of the neural cells is essential for this approach. This study investigates the viability of postnatal cortical rat cells that were dielectrophoretically trapped. Morphological characteristics as well as the ratio of the number of outgrowing to the number of non-outgrowing cortical cells were used to compare the viability of trapped cells to that of non-exposed cells. The morphological characteristics include the area of the cell, representing adhesive properties, and the number and length of the processes, as a measure for functional recovery. The results presented in this paper show that the viable state of dielectrophoretically trapped postnatal cortical rat cells under the conditions used was similar to that of non-exposed cells.

Animals↗
PubMed2001

Dielectrophoretic trapping of dissociated fetal cortical rat neurons.

Recording and stimulating neuronal activity at multiple sites can be realized with planar microelectrode arrays. Efficient use of such arrays requires each site to be covered by at least one neuron. By application of dielectrophoresis (DEP), neurons can be trapped onto these sites. This study investigates negative dielectrophoretic trapping of fetal cortical rat neurons. A planar quadrupole microelectrode structure was used for the creation of a nonuniform electric field. The field was varied in amplitude (1, 3, and 5 V) and frequency (10 kHz-50 MHz). Experimental results were compared with a theoretical model to investigate the yield (the number of neurons trapped in the center of the electrode structure) with respect to time, amplitude and frequency of the field. The yield was a function of time(1/3) according to theory. However, unlike the model predicted, an amplitude-dependent frequency behavior was present and unexpected peaks occurred in the DEP-spectra above 1 MHz. Gain/phase measurements showed a rather unpredictable behavior of the electrode plate above 1 MHz, and temperature measurement showed that heating of the medium influenced the trapping effect, especially for larger amplitudes and higher frequencies.

Animals↗
PubMed2000

Adhesion and patterning of cortical neurons on polyethylenimine- and fluorocarbon-coated surfaces.

Adhesion and patterning of cortical neurons was investigated on isolated islands of neuron-adhesive polyethylenimine (PEI) surrounded by a neuron-repellent fluorocarbon (FC) layer. In addition, the development of fasciculated neurites between the PEI-coated areas was studied over a time period of fifteen days. The patterns consisted of PEI-coated wells (diameter 150 microns, depth 0.5 micron) which were etched in a coating of fluorocarbon (FC) on top of polyimide (PI) coated glass. The separation distance between the PEI-coated wells were varied between 10 and 90 microns. This paper shows that chemical patterns of PEI and FC result in highly compliant patterns of adhering cortical neurons after one day in vitro. Interconnecting neurite fascicles between PEI-coated wells were especially present on patterns with a separation distance of 10 microns after eight days in vitro. A significant lower number of interconnecting neurite fascicles was observed on 20 microns separated patterns. Effective isolation of neurons into PEI-coated wells was achieved on patterns with a separation distance of 80 microns as no interconnecting neurite fascicles were observed.

Animals↗
PubMed1999

Endoneural selective stimulating using wire-microelectrode arrays.

In acute experiments eight 5- to 24-wire-microelectrode arrays were inserted into the common peroneal nerve of the rat, to investigate whether the electrodes could selectively stimulate motor units of the extensor digitorum longus (EDL) muscle. Twitch-force-recruitment curves were measured from the EDL for each array electrode. The curves were plotted on a double-logarithmic scale and parameterized by the low-force slope (which represents the power p in the power-law relationship of force F versus stimulus current I, or F approximately I(p)) and the threshold current. The slopes and threshold currents measured with array electrodes did not differ significantly from those obtained with randomly inserted single wire-microelectrodes. This indicates that, although involving a more invasive insertion procedure, electrode arrays provide neural contacts with low-force recruitment properties similar to those of single wires. Array results revealed partial blocking of neural conduction, similar to that reported with microneurographic insertion with single needles. The efficiency of the array was defined as the fraction of array electrodes selectively contacting a motor unit and evoking the corresponding threshold force. Efficiency thus expresses the practical value of the used electrode array in terms of the total number of distinct threshold forces that can be stimulated by selecting the appropriate electrodes. The eight arrays were capable of evoking threshold forces selectively with an average efficiency of 0.81 (or 81%).

Animals↗
PubMed1998

Force-current relationships in intraneural stimulation: role of extraneural medium and motor fibre clustering.

Animal experiments and model simulations of monopolar, intrafascicular nerve stimulation are presented to study force-current relationships (recruitment curves). The conductivity of the extraneural medium is of prime importance to the resulting recruitment cures: an insulating extraneural medium generally leads to steeper curves with lower threshold currents than a well-conducting extraneural medium. Extensive statistical comparison of experimental and model results suggests the occurrence of clustering of alpha-motoneurons within the fascicle, manifesting itself mainly by an increased spread in threshold currents, as opposed to the situation where the fibres are distributed uniformly throughout the entire fascicle.

Animals↗
PubMed1998

Measurement of sealing resistance of cell-electrode interfaces in neuronal cultures using impedance spectroscopy.

Sealing resistance is highly significant with respect to the electrical neuron-electrode contact because it decreases the stimulation threshold of neurons cultured on a planar micro-electrode array. A method is proposed for measurement of the sealing resistance using impedance spectroscopy. The effect of the sealing resistance on the total impedance spectrum of a cell-electrode interface is modelled for complete coverage of the electrode by the cell. Sensitivity analysis demonstrates that the impedance spectrum is determined by four parameters: two electrode parameters, the sealing resistance and the shunt capacitance between the lead of the electrode and the culture medium. Experimental verification of the model is performed by simultaneous measurement of the impedance spectrum and electrode coverage. A good and unique fit between the simulated and measured impedance spectra was obtained by varying the two electrode parameters and the sealing resistance.

Animals↗
PubMed1998

Glass ring-wall sealing to prevent leakage from electrode culture chambers: a technical note.

Entellan is a good sealing substance for culture chamber walls and does not interfere with the growth of the cultured DRG cells. If the Entellan becomes brittle the glass ring can easily be loosened by placing the chamber with the sealed ring for 24 hrs in xylene. Repeated rinsing with xylene and subsequently with hydrated steps of ethanol (100%-70%-30%) allows the ring-wall and chamber floor with its electrodes to be reused.

Animals↗
PubMed1998

Extracellular potentials from active myelinated fibers inside insulated and noninsulated peripheral nerve.

A model is presented that calculates the single-fiber extracellular field and action potential (ap) of an active myelinated nerve fiber placed centrally or eccentrically inside a nerve with a cylindrical geometry, representing essentially a one-fascicle nerve. This one-fascicle nerve has the dimensions and conductivities of the rat peroneal nerve branch. The results show a wide variety of wave shapes to be measured, depending on the position of the intraneural electrode with respect to the fiber axis and to the nodes of Ranvier and depending on the presence of an isolating cuff around the nerve. Action potential shapes may range from the "classical" quasi-biphasic one, to more triphasic, or even more complicated in the case of a short insulating cuff being present around the nerve. In the latter case, when measured bipolarly, ap-wave shapes become almost monophasic.

Action Potentials↗
PubMed1997

Influence of inhomogeneities in muscle tissue on single-fibre action potentials: a model study.

The influence of changes in electrical conductivity, due to the muscle boundary, layers and compartments of intramuscular connective tissue and blood vessels, on computed single-muscle fibre action potentials (SFAPs) in rat hindleg muscle is calculated. The position of the active fibre is varied throughout the muscle. For fibres close to the muscle boundary, peak-to-peak voltages of SFAPs increase by up to a factor of 3 compared with the unbounded situation. For inner fibres, the presence of nearby connective tissue compartments causes an increase of up to 40%. A blood vessel in the neighbourhood of the active fibre leads to a decrease of at most 20%, for recording sites between the active fibre and the blood vessel. For recording sites beyond the blood vessel, peak-to-peak voltages increase by up to 20%.

Action Potentials↗
PubMed1995

Force recruitment during electrical nerve stimulation with multipolar intrafascicular electrodes.

Experimentally, during electrical nerve stimulation, the influence is examined of two intrafascicular anodes on the force recruitment with one intrafascicular cathode. It is found that the anodes suppress recruitment and that this effect is more pronounced when the distance of the anodes to the cathode is decreased, or when the anodal currents are increased. The measured recruitment curve patterns can be qualitatively explained by a nerve stimulation model that calculates theoretical recruitment curves for intrafascicular multi-electrode configurations. Discrepancies between the experimental and the theoretical recruitment curves are seen, but these can be understood by taking into account a non-uniform fibre distribution.

Animals↗
PubMed1995

3D neuro-electronic interface devices for neuromuscular control: design studies and realisation steps.

In order to design the shape and dimensions of new 3D multi-microelectrode information transducers properly, i.e. adapted to the scale of information delivery to and from peripheral nerve fibres, a number of studies were, and still are, being performed on modelling and simulation of electrical volume conduction inside and outside nerves, on animal experiments on stimulation and recording with single wires and linear arrays, and on new technologies for 3D micro-fabrication. This paper presents a selection of the results of these "Neurotechnology' studies at the University of Twente. The experimental and simulation results apply primarily to the peripheral motor nerves of the rat, but are also of interest for neural interfacing with myelinated nerves in man, as fascicles in man are about the same size as in the rat.

Animals↗
PubMed1993

Reconstructing muscle activation during normal walking: a comparison of symbolic and connectionist machine learning techniques.

One symbolic (rule-based inductive learning) and one connectionist (neural network) machine learning technique were used to reconstruct muscle activation patterns from kinematic data measured during normal human walking at several speeds. The activation patterns (or desired outputs) consisted of surface electromyographic (EMG) signals from the semitendinosus and vastus medialis muscles. The inputs consisted of flexion and extension angles measured at the hip and knee of the ipsilateral leg, their first and second derivatives, and bilateral foot contact information. The training set consisted of data from six trials, at two different speeds. The testing set consisted of data from two additional trials (one at each speed), which were not in the training set. It was possible to reconstruct the muscular activation at both speeds using both techniques. Timing of the reconstructed signals was accurate. The integrated value of the activation bursts was less accurate. The neural network gave a continuous output, whereas the rule-based inductive learning rule tree gave a quantised activation level. The advantage of rule-based inductive learning was that the rules used were both explicit and comprehensible, whilst the rules used by the neural network were implicit within its structure and not easily comprehended. The neural network was able to reconstruct the activation patterns of both muscles from one network, whereas two separate rule sets were needed for the rule-based technique. It is concluded that machine learning techniques, in comparison to explicit inverse muscular skeletal models, show good promise in modelling nearly cyclic movements such as locomotion at varying walking speeds.(ABSTRACT TRUNCATED AT 250 WORDS)

Algorithms↗
PubMed1993

The bioelectrical source in computing single muscle fiber action potentials.

Generally, single muscle fiber action potentials (SFAPs) are modeled as a convolution of the bioelectrical source (being the transmembrane current) with a weighting or transfer function, representing the electrical volume conduction. In practice, the intracellular action potential (IAP) rather than the transmembrane current is often used as the source, because the IAP is relatively easy to obtain under experimental conditions. Using a core conductor assumption, the transmembrane current equals the second derivative of the IAP. In previous articles, discrepancies were found between experimental and simulated SFAPs. Adaptations in the volume conductor slightly altered the simulation results. Another origin of discrepancy might be an erroneous description of the source. Therefore, in the present article, different sources were studied. First, an analytical description of the IAP was used. Furthermore, an experimental IAP, a special experimental SFAP, and a measured transmembrane current scaled to our experimental situation were applied. The results for the experimental IAP were comparable to those with the analytical IAP. The best agreement between experimental and simulated data was found for a measured transmembrane current as source, but differences are still apparent.

Action Potentials↗
PubMed1992

Potential distribution and single-fibre action potentials in a radially bounded muscle model.

In modelling the electrical behaviour of muscle tissue, we used to employ a frequency-dependent volume conductor network model, which was infinitely extended in all directions. Equations in this model could be solved using a finite-difference approach. The most important restriction of this model was the fact that no boundary effects could be incorporated. Analytical models of muscle tissue normally do not have this disadvantage, but in those models the microscopic structure of muscle tissue cannot be taken into account. In the paper, we present a combined numerical/analytical approach, which enables the study of potential distributions and SFAPs in simulated microscopic muscle tissue in which the influence of the muscle boundary has been considered. We considered muscle models with radii of 1.5 mm and 10 mm. Both models were compared with an unbounded network model. In the model with a radius of 1.5 mm we varied the position of the active fibre relative to the muscle surface. It appeared that in most cases the presence of a boundary had a considerable effect on the potential distribution. An increase in the peak-to-peak value of the SFAP amplitude up to 300 per cent was noticed when the active fibre was positioned 500 microns beneath the muscle surface in a model with a radius of 1.5 mm.

Action Potentials↗
PubMed1992

Simulation of multipolar fiber selective neural stimulation using intrafascicular electrodes.

A realistic, quantitative model is presented for the excitation of myelinated nerve fibers by intrafascicular electrodes. It predicts the stimulatory regions of any configuration of any number of electrodes, positioned anywhere inside the fascicle. The model has two parts. First, the nerve fiber is represented by a lumped electrical network and its response to an arbitrary extracellular potential field is calculated. Second, assuming a cylindrical geometry of the nerve bundle and its surroundings, an analytical expression for this field is derived. With realistic parameters, the model is applied to two cases: monopolar stimulation by a single cathode and stimulation by a specific tripolar configuration. It is shown that tripolar stimulation has the better spatial selectivity. Also tripolar stimulation is less sensitive to the conductivity of the medium surrounding the nerve and yields a more natural recruitment order.

Electric Conductivity↗
PubMed1991

Selectivity of intraneural prosthetic interfaces for muscular control.

Intraneural stimulation with multi-electrodes in principle offers the best possibilities to reach selectivity at motor unit level and to improve recruitment order. The selectivity of stimulation in the peroneal nerve of the rat is explored in the paper by calculations and measurements, using a linear 12-electrode array and a newly devised selectivity test method. With analytical models for potential field distributions, areas of excitation can be calculated for arbitrary electrode configurations. It is demonstrated, using tripolar electrode combinations, how selectivity can be further enhanced and recruitment order improved.

Action Potentials↗
PubMed1991

Sensitivity and selectivity of intraneural stimulation using a silicon electrode array.

Artificial electrical stimulation of peripheral nerves needs the development of multielectrode devices which stimulate individual fibers or small groups in a selective and sensitive way. To this end, a multielectrode array in silicon technology has been developed, as well as experimental paradigms and model calculations for sensitivity and selectivity measures. The array consists of twelve platinum electrode sites (10 x 50 microns at 50 microns interdistance) on a 45 microns thick tip-shaped silicon substrate and a Si3N4 insulating glass cover layer. The tip is inserted in the peroneal nerve of the rat during acute experiments to stimulate alpha motor fibers of the extensor digitorum longus muscle. Sensitivity calculations and experiments show a cubic dependence of the number of stimulated motor units on current amplitude of the stimulatory pulse (recruitment curves), starting at single motor level. Selectivity was tested by a method based on the refractory properties of neurons. At the lowest stimulus levels (for one motor unit) selectivity is maximal when two electrodes are separated by 200-250 microns, which was estimated also on theoretical grounds. The study provides clues for future designs of two- and three-dimensional devices.

Animals↗