Marc Heuschkel - Academia.edu (original) (raw)

Papers by Marc Heuschkel

Frontiers in Neuroscience, Jun 15, 2023

Opening the black box of traumatic brain injury: a holistic approach combining human D neural tis... more Opening the black box of traumatic brain injury: a holistic approach combining human D neural tissue and an in vitro traumatic brain injury induction device.

By enhancing the environment of micro electrode arrays with microfluidic channels we cultured pri... more By enhancing the environment of micro electrode arrays with microfluidic channels we cultured primary neuronal cells in patterned two- and three dimensional structures. Alternatively, the same microfluidic channels can be used to generate a local chemical stimulation over a two-dimensional neuronal cell culture. We demonstrate that a significantly different of spontaneous activity pattern was recorded from the same neuronal cell culture under perfusion of 4.5μM bicuculline at 20 nl/s and 200 nl/s.

These Ecole polytechnique federale de Lausanne EPFL, n° 2370 (2001)Faculte des sciences et techni... more These Ecole polytechnique federale de Lausanne EPFL, n° 2370 (2001)Faculte des sciences et techniques de l'ingenieurLaboratoire de microsystemes 4Jury: Daniel Bertrand, Hannes Bleuler, Ulrich Egert, Philippe Flueckiger, Milena Koudelka-Hep, Horst Vogel Public defense: 2001-4-20 Reference doi:10.5075/epfl-thesis-2370Print copy in library catalog Record created on 2005-03-16, modified on 2017-05-10

Neurodegenerative Diseases, 2015

This paper describes the development of microelectrodes with integrated three-dimensional electro... more This paper describes the development of microelectrodes with integrated three-dimensional electrode structures. The integration of three-dimensional structures aims at an improvement of the electrode/tissue interface. Due to the increase in surface area the electrode impedance is reduced, while the density of microelectrodes per area remains the same as with flat electrodes. Two different types of electrodes have been developed: Flexible, implantable microelectrodes with pyramidal, protruding structures and tip-shaped electrode arrays on glass substrates. The protrusion heights of the electrode sites can easily be adjusted depending on the actual application. For the flexible structures we used a polyimidebased process to fabricate microelectrodes with sharp or flat pyramidal tips and with electrode arrangements on front and backside of the devices. The tip-shaped electrode arrays were fabricated from a glass substrate by isotropic wet chemical etching and subsequent metallization and passivation. Data from impedance measurements and acute brain slice recordings indicate a considerable improvement regarding electrode impedance and obtainable signal strength.

European Journal of Neuroscience, Jul 1, 2001

Rat spinal networks generate a spontaneous rhythmic output directed to motoneurons under conditio... more Rat spinal networks generate a spontaneous rhythmic output directed to motoneurons under conditions of increased excitation or of disinhibition. It is not known whether these differently induced rhythms are produced by a common rhythm generator. To investigate the generation and the propagation of rhythmic activity in spinal networks, recordings need to be made from many neurons simultaneously. Therefore extracellular multisite recording was performed in slice cultures of embryonic rat spinal cords grown on multielectrode arrays. In these organotypic cultures most of the spontaneous neural activity was nearly synchronized. Waves of activity spread from a source to most of the network within 35±85 ms and died out after a further 30±400 ms. Such activity waves induced the contraction of cocultured muscle ®bres. Several activity waves could be grouped into aperiodic bursts. Disinhibition with bicuculline and strychnine or increased excitability with high K + or low Mg 2+ solutions could induce periodic bursting with bursts consisting of one or several activity waves. Whilst the duration and period of activity waves were similar for all protocols, the duration and period of bursts were longer during disinhibition than during increased excitation. The sources of bursting activity were mainly situated ventrally on both sides of the central ®ssure. The pathways of network recruitment from one source were variable between bursts, but they showed on average no systematic differences between the protocols. These spatiotemporal similarities under conditions of increased excitation and of disinhibition suggest a common spinal network for both types of rhythmic activity.

European Journal of Neuroscience, Jul 1, 2001

Locomotion in vertebrates is controlled by central pattern generators in the spinal cord. The rol... more Locomotion in vertebrates is controlled by central pattern generators in the spinal cord. The roles of speci®c network architecture and neuronal properties in rhythm generation by such spinal networks are not fully understood. We have used multisite recording from dissociated cultures of embryonic rat spinal cord grown on multielectrode arrays to investigate the patterns of spontaneous activity in randomised spinal networks. We were able to induce similar patterns of rhythmic activity in dissociated cultures as in slice cultures, although not with the same reliability and not always with the same protocols. The most reliable rhythmic activity was induced when a partial disinhibition of the network was combined with an increase in neuronal excitability, suggesting that both recurrent synaptic excitation and neuronal excitability contribute to rhythmogenesis. During rhythmic activity, bursts started at several sites and propagated in variable ways. However, the predominant propagation patterns were independent of the protocol used to induce rhythmic activity. When synaptic transmission was blocked by CNQX, APV, strychnine and bicuculline, asynchronous low-rate activity persisted at » 50% of the electrodes and » 70% of the sites of burst initiation. Following the bursts, the activity in the interval was transiently suppressed below the level of intrinsic activity. The degree of suppression was proportional to the amount of activity in the preceding burst. From these ®ndings we conclude that rhythmic activity in spinal cultures is controlled by the interplay of intrinsic neuronal activity and recurrent excitation in neuronal networks without the need for a speci®c architecture.

Springer eBooks, Oct 22, 2006

Circulation Research, Jun 9, 2000

It is known that extracardiac factors (nervous, humoral, and hemodynamic) participate in the powe... more It is known that extracardiac factors (nervous, humoral, and hemodynamic) participate in the power-law behavior of heart-rate variability. To assess whether intrinsic properties of cardiac tissue might also be involved, beat-rate variability was studied in spontaneously beating cell cultures devoid of extracardiac influences. Extracellular electrograms were recorded from monolayer cultures of neonatal rat ventricular myocytes under stable incubating conditions for up to 9 hours. The beat-rate time series of these recordings were examined in terms of their Fourier spectra and their Hurst scaling exponents. A non-0 Hurst exponent was found in 21 of 22 preparations (0.29Ϯ0.09; range, 0.11 to 0.45), indicating the presence of fractal self-similarity in the beat-rate time series. The same preparations exhibited power-law behavior of the power spectra with a power-law exponent of Ϫ1.36Ϯ0.24 (range, Ϫ1.04 to Ϫ1.96) in the frequency range of 0.001 to 1 Hz. Furthermore, it was found that the power-law exponent was nonstationary over time. These results indicate that the power-law behavior of heart-rate variability is determined not only by extracardiac influences but also by components intrinsic to cardiac tissue. Furthermore, the presence of power-law behavior in monolayer cultures of cardiomyocytes suggests that beat-rate variability might be determined by the complex nonlinear dynamics of processes occurring at the level of the cellular network, eg, interactions among a large number of cell oscillators or metabolic regulatory systems.

Journal of Neuroscience Methods, Mar 1, 2002

Several multi-electrode array devices integrating planar metal electrodes were designed in the pa... more Several multi-electrode array devices integrating planar metal electrodes were designed in the past 30 years for extracellular stimulation and recording from cultured neuronal cells and organotypic brain slices. However, these devices are not well suited for recordings from acute brain slice preparations due to a dead cell layer at the tissue slice border that appears during the cutting procedure. To overcome this problem, we propose the use of protruding 3D electrodes, i.e. tip-shaped electrodes, allowing tissue penetration in order to get closer to living neurons in the tissue slice. In this paper, we describe the design and fabrication of planar and 3D protruding multi-electrode arrays. The electrical differences between planar and 3D protruding electrode configuration were simulated and verified experimentally. Finally, a comparison between the planar and 3D protruding electrode configuration was realized by stimulation and recording from acute rat hippocampus slices. The results show that larger signal amplitudes in the millivolt range can be obtained with the 3D electrode devices. Spikes corresponding to single cell activity could be monitored in the hippocampus CA3 and CA1 region using 3D electrodes.

Analytical Chemistry, Dec 17, 2005

Microarray technology is a powerful tool that provides a high throughput of bioanalytical informa... more Microarray technology is a powerful tool that provides a high throughput of bioanalytical information within a single experiment. These miniaturized and parallelized binding assays are highly sensitive and have found widespread popularity especially during the genomic era. However, as drug diagnostics studies are often targeted at membrane proteins, the current arraying technologies are ill-equipped to handle the fragile nature of the protein molecules. In addition, to understand the complex structure and functions of proteins, different strategies to immobilize the probe molecules selectively onto a platform for protein microarray are required. We propose a novel approach to create a (membrane) protein microarray by using an indium tin oxide (ITO) microelectrode array with an electronic multiplexing capability. A polycationic, protein- and vesicle-resistant copolymer, poly(l-lysine)-grafted-poly(ethylene glycol) (PLL-g-PEG), is exposed to and adsorbed uniformly onto the microelectrode array, as a passivating adlayer. An electronic stimulation is then applied onto the individual ITO microelectrodes resulting in the localized release of the polymer thus revealing a bare ITO surface. Different polymer and biological moieties are specifically immobilized onto the activated ITO microelectrodes while the other regions remain protein-resistant as they are unaffected by the induced electrical potential. The desorption process of the PLL-g-PEG is observed to be highly selective, rapid, and reversible without compromising on the integrity and performance of the conductive ITO microelectrodes. As such, we have successfully created a stable and heterogeneous microarray of biomolecules by using selective electronic addressing on ITO microelectrodes. Both pharmaceutical diagnostics and biomedical technology are expected to benefit directly from this unique method.

Journal of Neuroscience Methods, Sep 1, 2006

There is increasing interest in interfacing dissociated neuronal cultures with planar multielectr... more There is increasing interest in interfacing dissociated neuronal cultures with planar multielectrode arrays (MEAs) for the study of the dynamics of neuronal networks. Here we report on the successful use of three-dimensional tip electrode arrays (3D MEAs), originally developed for use with brain slices, for recording and stimulation of cultured neurons. We observed that many neurons grew directly on protruding electrode surface, appearing to make excellent contact. A larger than usual portion of extracellular spikes had large positive peaks, while most of the spikes from conventional two-dimensional electrode arrays had large negative spikes. This may be due to the direct capacitive coupling situation provided by relatively large electrode surface area.

Micromachines, Dec 7, 2015

Polydimethylsiloxane (PDMS) and SU-8 are currently two very commonly used polymeric materials in ... more Polydimethylsiloxane (PDMS) and SU-8 are currently two very commonly used polymeric materials in the microfluidics field for biological applications. However, there is a pressing need to find a simple, reliable, irreversible bonding method between these two materials for their combined use in innovative integrated microsystems. In this paper, we attempt to investigate the aminosilane-mediated irreversible bonding method for PDMS and SU-8 with X-Ray Photoelectron Spectroscopy (XPS) surface analysis and bonding strength tests. Additionally, the selected bonding method was applied in fabricating a microelectrode array (MEA) device, including microfluidic features, which allows electrophysiological observations on compartmentalized neuronal cultures. As there is a growing trend towards microfluidic devices for neuroscience research, this type of integrated microdevice, which can observe functional alterations on compartmentalized neuronal culture, can potentially be used for neurodegenerative disease research and pharmaceutical development.

Biomedical Physics & Engineering Express, Sep 20, 2016

Objective. The importance of extracellular neural stimulation has driven the development of multi... more Objective. The importance of extracellular neural stimulation has driven the development of multiple technologies. Of growing importance is accurately stimulating single neurons in dense networks. It is unlikely that one approach is best for all applications, however comparisons between methods are lacking. We aim to show the strengths and suitable applications for two tools; micro-electrode array (MEA) stimulation and optogenetics. Approach. We compare MEA-based electrical stimulation to Channelrhodopsin 2 based optogenetic stimulation of dissociated cortical neurons in vitro. Effectivity is compared based on stimulation success rate, spatial and temporal accuracy, and reproducibility. We discuss how necessities of each method may limit performance in each category. Main Results. MEA stimulation outperformed optogenetic stimulation in the speed with which an action potential could be generated. The relation between the size of the stimulating point (electrode or illumination spot) and the area of stimulated tissue was similar in both methods. However, technical difficulties in maintaining low impedance from very small electrodes allows higher spatial specificity in optogenetic stimulation. If simultaneous recording and stimulation are desired, MEA stimulation artifacts were far more impairing than light induce artifacts on MEA recordings. Significance. The like versus like comparison of stimulation technologies provides an incomplete evaluation tool for researchers desiring to apply these technologies. This comparison highlights advantages for specific applications and should promote more cross-topic evaluations.

Since their introduction, Micro-Electrode Arrays (MEAs) have been exploited as devices providing ... more Since their introduction, Micro-Electrode Arrays (MEAs) have been exploited as devices providing distributed information about learning, memory and information processing in a cultured neuronal network, thus changing the field of view from single cell level (glass pipettes) to the scale of the complex network. MEAs represent a growing technology for the study of the functional activity of neuronal networks providing the possibility to gain information about the spatio-temporal dynamics of the network and to allow recordings of electrical activity over periods of time not compatible with conventional electrodes at several sites in parallel. More recently, according to the trend aimed at the reduction of animal tests, MEAs have been exploited as in vitro biosensors to monitor both acute and chronic effects of drugs on neuronal networks in physiological or pathophysiological conditions. On the contrary, the presence of stimulus artefacts and the poorly controlled spread of electrical s...

2001 Conference Proceedings of the 23rd Annual International Conference of the IEEE Engineering in Medicine and Biology Society

This paper describes the development of microelectrodes with integrated three-dimensional electro... more This paper describes the development of microelectrodes with integrated three-dimensional electrode structures. The integration of three-dimensional structures aims at an improvement of the electrode/tissue interface. Due to the increase in surface area the electrode impedance is reduced, while the density of microelectrodes per area remains the same as with flat electrodes. Two different types of electrodes have been developed: Flexible, implantable microelectrodes with pyramidal, protruding structures and tip-shaped electrode arrays on glass substrates. The protrusion heights of the electrode sites can easily be adjusted depending on the actual application. For the flexible structures we used a polyimidebased process to fabricate microelectrodes with sharp or flat pyramidal tips and with electrode arrangements on front and backside of the devices. The tip-shaped electrode arrays were fabricated from a glass substrate by isotropic wet chemical etching and subsequent metallization and passivation. Data from impedance measurements and acute brain slice recordings indicate a considerable improvement regarding electrode impedance and obtainable signal strength.

Novel Approaches in Biosensors and Rapid Diagnostic Assays, 2000

Although tobacco smoking is widespread in the population and some of its toxic effects are widely... more Although tobacco smoking is widespread in the population and some of its toxic effects are widely recognized the mechanisms underlying nicotine addiction and its toxicity still remain poorly understood. An important step toward this understanding was made with functional studies of nicotinic receptors reconstituted in host systems. However, it becomes increasingly important to understand their role in more physiological conditions. Namely, it is mandatory to be able to examine their contribution in a natural neuronal network. One of the best possible approaches would be to dispose of multiple electrode recordings that would allow investigation of acute brain slices. While planar multielectrode arrays constitute one possibility for multiple recordings of neurones in culture their signal noise ratio is, however, not sufficient for acute slices. To overcome this problem we are currently developing a “fakir bed” electrode array in which the electrode tips are brought in closer contact with intact neurones within the slice. In addition to being expressed by neurones, nicotinic acetylcholine receptors are also expressed in other cells throughout the body. For instance it has been shown that white blood cells express significant amount of these proteins and that nicotine can modulate the motility abilities of leukocytes. In a series of experiments we have been able to study these cellular processes in more detail and have established a new biochip technology with the aim of automatic evaluation of cell motility.

IFMBE Proceedings, 2009

ABSTRACT For historical reasons, the signal transduction interface of bioelectronic devices is co... more ABSTRACT For historical reasons, the signal transduction interface of bioelectronic devices is commonly based on metals or inorganic (semi-)conductors. This also applies to application areas where artificial components such as biomedical screening devices, in vitro microelectrode arrays and in vivo neuroprosthetics come into direct contact with biological tissue. In a proof-of-concept microelectrode array design study, we present an alternative all-polymer approach for the low-cost fabrication of bioelectrical signal transduction devices with adjustable flexibility, electrical impedance and transparency. The fabrication process entailed three steps. Firstly, by means of a replica-moulding strategy, different types of transparent polymers were microstructured by two-level SU-8 masters to create vias for contact pads and electrodes, and indentations for interconnecting microchannels. Secondly, recesses in the insulating polymer sheets were filled with conductive polymer composites based on quasi-transparent polystyrenesulfonate doped poly(3,4-ethylenedioxy-thiophene) (PEDOT:PSS). In a last step, the passive microelectrode arrays were backside-insulated by a second layer of a transparent polymer. The electrical properties of the resulting polymer microelectrode arrays were characterized by impedance spectroscopy, baseline noise measurements and recordings of bioelectrical signals from acute preparations of chicken cardiomyocytes. Biocompatibility was tested with in vitro cultures of cortical neurons derived from embryonic chicken. KeywordsNeural interfaces-microelectrode arrays-replica moulding-PDMS-PEDOT:PSS electroconductive polymer

Frontiers in Neuroengineering, 2009

The design of novel bidirectional interfaces for in vivo and in vitro nervous systems is an impor... more The design of novel bidirectional interfaces for in vivo and in vitro nervous systems is an important step towards future functional neuroprosthetics. Small electrodes, structures and devices are necessary to achieve high-resolution and target-selectivity during stimulation and recording of neuronal networks, while signifi cant charge transfer and large signal-to-noise ratio are required for accurate time resolution. In addition, the physical properties of the interface should remain stable across time, especially when chronic in vivo applications or in vitro long-term studies are considered, unless a procedure to actively compensate for degradation is provided. In this short report, we describe the use and fabrication of arrays of 120 planar microelectrodes (MEAs) of sputtered Iridium Oxide (IrOx). The effective surface area of individual microelectrodes is signifi cantly increased using electrochemical activation, a procedure that may also be employed to restore the properties of the electrodes as required. The electrode activation results in a very low interface impedance, especially in the lower frequency domain, which was characterized by impedance spectroscopy. The increase in the roughness of the microelectrodes surface was imaged using digital holographic microscopy and electron microscopy. Aging of the activated electrodes was also investigated, comparing storage in saline with storage in air. Demonstration of concept was achieved by recording multiple single-unit spike activity in acute brain slice preparations of rat neocortex. Data suggests that extracellular recording of action potentials can be achieved with planar IrOx MEAs with good signal-to-noise ratios.

Frontiers in Neuroscience

Traumatic brain injury (TBI) is caused by a wide range of physical events and can induce an even ... more Traumatic brain injury (TBI) is caused by a wide range of physical events and can induce an even larger spectrum of short- to long-term pathophysiologies. Neuroscientists have relied on animal models to understand the relationship between mechanical damages and functional alterations of neural cells. These in vivo and animal-based in vitro models represent important approaches to mimic traumas on whole brains or organized brain structures but are not fully representative of pathologies occurring after traumas on human brain parenchyma. To overcome these limitations and to establish a more accurate and comprehensive model of human TBI, we engineered an in vitro platform to induce injuries via the controlled projection of a small drop of liquid onto a 3D neural tissue engineered from human iPS cells. With this platform, biological mechanisms involved in neural cellular injury are recorded through electrophysiology measurements, quantification of biomarkers released, and two imaging me...

Frontiers in Neuroscience, Jun 15, 2023

Opening the black box of traumatic brain injury: a holistic approach combining human D neural tis... more Opening the black box of traumatic brain injury: a holistic approach combining human D neural tissue and an in vitro traumatic brain injury induction device.

By enhancing the environment of micro electrode arrays with microfluidic channels we cultured pri... more By enhancing the environment of micro electrode arrays with microfluidic channels we cultured primary neuronal cells in patterned two- and three dimensional structures. Alternatively, the same microfluidic channels can be used to generate a local chemical stimulation over a two-dimensional neuronal cell culture. We demonstrate that a significantly different of spontaneous activity pattern was recorded from the same neuronal cell culture under perfusion of 4.5μM bicuculline at 20 nl/s and 200 nl/s.

These Ecole polytechnique federale de Lausanne EPFL, n° 2370 (2001)Faculte des sciences et techni... more These Ecole polytechnique federale de Lausanne EPFL, n° 2370 (2001)Faculte des sciences et techniques de l'ingenieurLaboratoire de microsystemes 4Jury: Daniel Bertrand, Hannes Bleuler, Ulrich Egert, Philippe Flueckiger, Milena Koudelka-Hep, Horst Vogel Public defense: 2001-4-20 Reference doi:10.5075/epfl-thesis-2370Print copy in library catalog Record created on 2005-03-16, modified on 2017-05-10

Neurodegenerative Diseases, 2015

This paper describes the development of microelectrodes with integrated three-dimensional electro... more This paper describes the development of microelectrodes with integrated three-dimensional electrode structures. The integration of three-dimensional structures aims at an improvement of the electrode/tissue interface. Due to the increase in surface area the electrode impedance is reduced, while the density of microelectrodes per area remains the same as with flat electrodes. Two different types of electrodes have been developed: Flexible, implantable microelectrodes with pyramidal, protruding structures and tip-shaped electrode arrays on glass substrates. The protrusion heights of the electrode sites can easily be adjusted depending on the actual application. For the flexible structures we used a polyimidebased process to fabricate microelectrodes with sharp or flat pyramidal tips and with electrode arrangements on front and backside of the devices. The tip-shaped electrode arrays were fabricated from a glass substrate by isotropic wet chemical etching and subsequent metallization and passivation. Data from impedance measurements and acute brain slice recordings indicate a considerable improvement regarding electrode impedance and obtainable signal strength.

European Journal of Neuroscience, Jul 1, 2001

Rat spinal networks generate a spontaneous rhythmic output directed to motoneurons under conditio... more Rat spinal networks generate a spontaneous rhythmic output directed to motoneurons under conditions of increased excitation or of disinhibition. It is not known whether these differently induced rhythms are produced by a common rhythm generator. To investigate the generation and the propagation of rhythmic activity in spinal networks, recordings need to be made from many neurons simultaneously. Therefore extracellular multisite recording was performed in slice cultures of embryonic rat spinal cords grown on multielectrode arrays. In these organotypic cultures most of the spontaneous neural activity was nearly synchronized. Waves of activity spread from a source to most of the network within 35±85 ms and died out after a further 30±400 ms. Such activity waves induced the contraction of cocultured muscle ®bres. Several activity waves could be grouped into aperiodic bursts. Disinhibition with bicuculline and strychnine or increased excitability with high K + or low Mg 2+ solutions could induce periodic bursting with bursts consisting of one or several activity waves. Whilst the duration and period of activity waves were similar for all protocols, the duration and period of bursts were longer during disinhibition than during increased excitation. The sources of bursting activity were mainly situated ventrally on both sides of the central ®ssure. The pathways of network recruitment from one source were variable between bursts, but they showed on average no systematic differences between the protocols. These spatiotemporal similarities under conditions of increased excitation and of disinhibition suggest a common spinal network for both types of rhythmic activity.

European Journal of Neuroscience, Jul 1, 2001

Locomotion in vertebrates is controlled by central pattern generators in the spinal cord. The rol... more Locomotion in vertebrates is controlled by central pattern generators in the spinal cord. The roles of speci®c network architecture and neuronal properties in rhythm generation by such spinal networks are not fully understood. We have used multisite recording from dissociated cultures of embryonic rat spinal cord grown on multielectrode arrays to investigate the patterns of spontaneous activity in randomised spinal networks. We were able to induce similar patterns of rhythmic activity in dissociated cultures as in slice cultures, although not with the same reliability and not always with the same protocols. The most reliable rhythmic activity was induced when a partial disinhibition of the network was combined with an increase in neuronal excitability, suggesting that both recurrent synaptic excitation and neuronal excitability contribute to rhythmogenesis. During rhythmic activity, bursts started at several sites and propagated in variable ways. However, the predominant propagation patterns were independent of the protocol used to induce rhythmic activity. When synaptic transmission was blocked by CNQX, APV, strychnine and bicuculline, asynchronous low-rate activity persisted at » 50% of the electrodes and » 70% of the sites of burst initiation. Following the bursts, the activity in the interval was transiently suppressed below the level of intrinsic activity. The degree of suppression was proportional to the amount of activity in the preceding burst. From these ®ndings we conclude that rhythmic activity in spinal cultures is controlled by the interplay of intrinsic neuronal activity and recurrent excitation in neuronal networks without the need for a speci®c architecture.

Springer eBooks, Oct 22, 2006

Circulation Research, Jun 9, 2000

It is known that extracardiac factors (nervous, humoral, and hemodynamic) participate in the powe... more It is known that extracardiac factors (nervous, humoral, and hemodynamic) participate in the power-law behavior of heart-rate variability. To assess whether intrinsic properties of cardiac tissue might also be involved, beat-rate variability was studied in spontaneously beating cell cultures devoid of extracardiac influences. Extracellular electrograms were recorded from monolayer cultures of neonatal rat ventricular myocytes under stable incubating conditions for up to 9 hours. The beat-rate time series of these recordings were examined in terms of their Fourier spectra and their Hurst scaling exponents. A non-0 Hurst exponent was found in 21 of 22 preparations (0.29Ϯ0.09; range, 0.11 to 0.45), indicating the presence of fractal self-similarity in the beat-rate time series. The same preparations exhibited power-law behavior of the power spectra with a power-law exponent of Ϫ1.36Ϯ0.24 (range, Ϫ1.04 to Ϫ1.96) in the frequency range of 0.001 to 1 Hz. Furthermore, it was found that the power-law exponent was nonstationary over time. These results indicate that the power-law behavior of heart-rate variability is determined not only by extracardiac influences but also by components intrinsic to cardiac tissue. Furthermore, the presence of power-law behavior in monolayer cultures of cardiomyocytes suggests that beat-rate variability might be determined by the complex nonlinear dynamics of processes occurring at the level of the cellular network, eg, interactions among a large number of cell oscillators or metabolic regulatory systems.

Journal of Neuroscience Methods, Mar 1, 2002

Several multi-electrode array devices integrating planar metal electrodes were designed in the pa... more Several multi-electrode array devices integrating planar metal electrodes were designed in the past 30 years for extracellular stimulation and recording from cultured neuronal cells and organotypic brain slices. However, these devices are not well suited for recordings from acute brain slice preparations due to a dead cell layer at the tissue slice border that appears during the cutting procedure. To overcome this problem, we propose the use of protruding 3D electrodes, i.e. tip-shaped electrodes, allowing tissue penetration in order to get closer to living neurons in the tissue slice. In this paper, we describe the design and fabrication of planar and 3D protruding multi-electrode arrays. The electrical differences between planar and 3D protruding electrode configuration were simulated and verified experimentally. Finally, a comparison between the planar and 3D protruding electrode configuration was realized by stimulation and recording from acute rat hippocampus slices. The results show that larger signal amplitudes in the millivolt range can be obtained with the 3D electrode devices. Spikes corresponding to single cell activity could be monitored in the hippocampus CA3 and CA1 region using 3D electrodes.

Analytical Chemistry, Dec 17, 2005

Microarray technology is a powerful tool that provides a high throughput of bioanalytical informa... more Microarray technology is a powerful tool that provides a high throughput of bioanalytical information within a single experiment. These miniaturized and parallelized binding assays are highly sensitive and have found widespread popularity especially during the genomic era. However, as drug diagnostics studies are often targeted at membrane proteins, the current arraying technologies are ill-equipped to handle the fragile nature of the protein molecules. In addition, to understand the complex structure and functions of proteins, different strategies to immobilize the probe molecules selectively onto a platform for protein microarray are required. We propose a novel approach to create a (membrane) protein microarray by using an indium tin oxide (ITO) microelectrode array with an electronic multiplexing capability. A polycationic, protein- and vesicle-resistant copolymer, poly(l-lysine)-grafted-poly(ethylene glycol) (PLL-g-PEG), is exposed to and adsorbed uniformly onto the microelectrode array, as a passivating adlayer. An electronic stimulation is then applied onto the individual ITO microelectrodes resulting in the localized release of the polymer thus revealing a bare ITO surface. Different polymer and biological moieties are specifically immobilized onto the activated ITO microelectrodes while the other regions remain protein-resistant as they are unaffected by the induced electrical potential. The desorption process of the PLL-g-PEG is observed to be highly selective, rapid, and reversible without compromising on the integrity and performance of the conductive ITO microelectrodes. As such, we have successfully created a stable and heterogeneous microarray of biomolecules by using selective electronic addressing on ITO microelectrodes. Both pharmaceutical diagnostics and biomedical technology are expected to benefit directly from this unique method.

Journal of Neuroscience Methods, Sep 1, 2006

There is increasing interest in interfacing dissociated neuronal cultures with planar multielectr... more There is increasing interest in interfacing dissociated neuronal cultures with planar multielectrode arrays (MEAs) for the study of the dynamics of neuronal networks. Here we report on the successful use of three-dimensional tip electrode arrays (3D MEAs), originally developed for use with brain slices, for recording and stimulation of cultured neurons. We observed that many neurons grew directly on protruding electrode surface, appearing to make excellent contact. A larger than usual portion of extracellular spikes had large positive peaks, while most of the spikes from conventional two-dimensional electrode arrays had large negative spikes. This may be due to the direct capacitive coupling situation provided by relatively large electrode surface area.

Micromachines, Dec 7, 2015

Polydimethylsiloxane (PDMS) and SU-8 are currently two very commonly used polymeric materials in ... more Polydimethylsiloxane (PDMS) and SU-8 are currently two very commonly used polymeric materials in the microfluidics field for biological applications. However, there is a pressing need to find a simple, reliable, irreversible bonding method between these two materials for their combined use in innovative integrated microsystems. In this paper, we attempt to investigate the aminosilane-mediated irreversible bonding method for PDMS and SU-8 with X-Ray Photoelectron Spectroscopy (XPS) surface analysis and bonding strength tests. Additionally, the selected bonding method was applied in fabricating a microelectrode array (MEA) device, including microfluidic features, which allows electrophysiological observations on compartmentalized neuronal cultures. As there is a growing trend towards microfluidic devices for neuroscience research, this type of integrated microdevice, which can observe functional alterations on compartmentalized neuronal culture, can potentially be used for neurodegenerative disease research and pharmaceutical development.

Biomedical Physics & Engineering Express, Sep 20, 2016

Objective. The importance of extracellular neural stimulation has driven the development of multi... more Objective. The importance of extracellular neural stimulation has driven the development of multiple technologies. Of growing importance is accurately stimulating single neurons in dense networks. It is unlikely that one approach is best for all applications, however comparisons between methods are lacking. We aim to show the strengths and suitable applications for two tools; micro-electrode array (MEA) stimulation and optogenetics. Approach. We compare MEA-based electrical stimulation to Channelrhodopsin 2 based optogenetic stimulation of dissociated cortical neurons in vitro. Effectivity is compared based on stimulation success rate, spatial and temporal accuracy, and reproducibility. We discuss how necessities of each method may limit performance in each category. Main Results. MEA stimulation outperformed optogenetic stimulation in the speed with which an action potential could be generated. The relation between the size of the stimulating point (electrode or illumination spot) and the area of stimulated tissue was similar in both methods. However, technical difficulties in maintaining low impedance from very small electrodes allows higher spatial specificity in optogenetic stimulation. If simultaneous recording and stimulation are desired, MEA stimulation artifacts were far more impairing than light induce artifacts on MEA recordings. Significance. The like versus like comparison of stimulation technologies provides an incomplete evaluation tool for researchers desiring to apply these technologies. This comparison highlights advantages for specific applications and should promote more cross-topic evaluations.

Since their introduction, Micro-Electrode Arrays (MEAs) have been exploited as devices providing ... more Since their introduction, Micro-Electrode Arrays (MEAs) have been exploited as devices providing distributed information about learning, memory and information processing in a cultured neuronal network, thus changing the field of view from single cell level (glass pipettes) to the scale of the complex network. MEAs represent a growing technology for the study of the functional activity of neuronal networks providing the possibility to gain information about the spatio-temporal dynamics of the network and to allow recordings of electrical activity over periods of time not compatible with conventional electrodes at several sites in parallel. More recently, according to the trend aimed at the reduction of animal tests, MEAs have been exploited as in vitro biosensors to monitor both acute and chronic effects of drugs on neuronal networks in physiological or pathophysiological conditions. On the contrary, the presence of stimulus artefacts and the poorly controlled spread of electrical s...

2001 Conference Proceedings of the 23rd Annual International Conference of the IEEE Engineering in Medicine and Biology Society

This paper describes the development of microelectrodes with integrated three-dimensional electro... more This paper describes the development of microelectrodes with integrated three-dimensional electrode structures. The integration of three-dimensional structures aims at an improvement of the electrode/tissue interface. Due to the increase in surface area the electrode impedance is reduced, while the density of microelectrodes per area remains the same as with flat electrodes. Two different types of electrodes have been developed: Flexible, implantable microelectrodes with pyramidal, protruding structures and tip-shaped electrode arrays on glass substrates. The protrusion heights of the electrode sites can easily be adjusted depending on the actual application. For the flexible structures we used a polyimidebased process to fabricate microelectrodes with sharp or flat pyramidal tips and with electrode arrangements on front and backside of the devices. The tip-shaped electrode arrays were fabricated from a glass substrate by isotropic wet chemical etching and subsequent metallization and passivation. Data from impedance measurements and acute brain slice recordings indicate a considerable improvement regarding electrode impedance and obtainable signal strength.

Novel Approaches in Biosensors and Rapid Diagnostic Assays, 2000

Although tobacco smoking is widespread in the population and some of its toxic effects are widely... more Although tobacco smoking is widespread in the population and some of its toxic effects are widely recognized the mechanisms underlying nicotine addiction and its toxicity still remain poorly understood. An important step toward this understanding was made with functional studies of nicotinic receptors reconstituted in host systems. However, it becomes increasingly important to understand their role in more physiological conditions. Namely, it is mandatory to be able to examine their contribution in a natural neuronal network. One of the best possible approaches would be to dispose of multiple electrode recordings that would allow investigation of acute brain slices. While planar multielectrode arrays constitute one possibility for multiple recordings of neurones in culture their signal noise ratio is, however, not sufficient for acute slices. To overcome this problem we are currently developing a “fakir bed” electrode array in which the electrode tips are brought in closer contact with intact neurones within the slice. In addition to being expressed by neurones, nicotinic acetylcholine receptors are also expressed in other cells throughout the body. For instance it has been shown that white blood cells express significant amount of these proteins and that nicotine can modulate the motility abilities of leukocytes. In a series of experiments we have been able to study these cellular processes in more detail and have established a new biochip technology with the aim of automatic evaluation of cell motility.

IFMBE Proceedings, 2009

ABSTRACT For historical reasons, the signal transduction interface of bioelectronic devices is co... more ABSTRACT For historical reasons, the signal transduction interface of bioelectronic devices is commonly based on metals or inorganic (semi-)conductors. This also applies to application areas where artificial components such as biomedical screening devices, in vitro microelectrode arrays and in vivo neuroprosthetics come into direct contact with biological tissue. In a proof-of-concept microelectrode array design study, we present an alternative all-polymer approach for the low-cost fabrication of bioelectrical signal transduction devices with adjustable flexibility, electrical impedance and transparency. The fabrication process entailed three steps. Firstly, by means of a replica-moulding strategy, different types of transparent polymers were microstructured by two-level SU-8 masters to create vias for contact pads and electrodes, and indentations for interconnecting microchannels. Secondly, recesses in the insulating polymer sheets were filled with conductive polymer composites based on quasi-transparent polystyrenesulfonate doped poly(3,4-ethylenedioxy-thiophene) (PEDOT:PSS). In a last step, the passive microelectrode arrays were backside-insulated by a second layer of a transparent polymer. The electrical properties of the resulting polymer microelectrode arrays were characterized by impedance spectroscopy, baseline noise measurements and recordings of bioelectrical signals from acute preparations of chicken cardiomyocytes. Biocompatibility was tested with in vitro cultures of cortical neurons derived from embryonic chicken. KeywordsNeural interfaces-microelectrode arrays-replica moulding-PDMS-PEDOT:PSS electroconductive polymer

Frontiers in Neuroengineering, 2009

The design of novel bidirectional interfaces for in vivo and in vitro nervous systems is an impor... more The design of novel bidirectional interfaces for in vivo and in vitro nervous systems is an important step towards future functional neuroprosthetics. Small electrodes, structures and devices are necessary to achieve high-resolution and target-selectivity during stimulation and recording of neuronal networks, while signifi cant charge transfer and large signal-to-noise ratio are required for accurate time resolution. In addition, the physical properties of the interface should remain stable across time, especially when chronic in vivo applications or in vitro long-term studies are considered, unless a procedure to actively compensate for degradation is provided. In this short report, we describe the use and fabrication of arrays of 120 planar microelectrodes (MEAs) of sputtered Iridium Oxide (IrOx). The effective surface area of individual microelectrodes is signifi cantly increased using electrochemical activation, a procedure that may also be employed to restore the properties of the electrodes as required. The electrode activation results in a very low interface impedance, especially in the lower frequency domain, which was characterized by impedance spectroscopy. The increase in the roughness of the microelectrodes surface was imaged using digital holographic microscopy and electron microscopy. Aging of the activated electrodes was also investigated, comparing storage in saline with storage in air. Demonstration of concept was achieved by recording multiple single-unit spike activity in acute brain slice preparations of rat neocortex. Data suggests that extracellular recording of action potentials can be achieved with planar IrOx MEAs with good signal-to-noise ratios.

Frontiers in Neuroscience

Traumatic brain injury (TBI) is caused by a wide range of physical events and can induce an even ... more Traumatic brain injury (TBI) is caused by a wide range of physical events and can induce an even larger spectrum of short- to long-term pathophysiologies. Neuroscientists have relied on animal models to understand the relationship between mechanical damages and functional alterations of neural cells. These in vivo and animal-based in vitro models represent important approaches to mimic traumas on whole brains or organized brain structures but are not fully representative of pathologies occurring after traumas on human brain parenchyma. To overcome these limitations and to establish a more accurate and comprehensive model of human TBI, we engineered an in vitro platform to induce injuries via the controlled projection of a small drop of liquid onto a 3D neural tissue engineered from human iPS cells. With this platform, biological mechanisms involved in neural cellular injury are recorded through electrophysiology measurements, quantification of biomarkers released, and two imaging me...