Influence of Auditory Cues on the Neuronal Response to Naturalistic Visual Stimuli in a Virtual Reality Setting

Virtual reality environments offer great opportunities to study the performance of brain-computer interfaces (BCIs) in real-world contexts. As real-world stimuli are typically multimodal, their neuronal integration elicits complex response patterns. To investigate the effect of additional auditory cues on the processing of visual information, we used virtual reality to mimic safety-related events in an industrial environment while we concomitantly recorded electroencephalography (EEG) signals. We simulated a box traveling on a conveyor belt system where two types of stimuli – an exploding and a burning box – interrupt regular operation. The recordings from 16 subjects were divided into two subsets, a visual-only and an audio-visual experiment. In the visual-only experiment, the response patterns for both stimuli elicited a similar pattern – a visual evoked potential (VEP) followed by an event-related potential (ERP) over the occipital-parietal lobe. Moreover, we found the perceived severity of the event to be reflected in the signal amplitude. Interestingly, the additional auditory cues had a twofold effect on the previous findings: The P1 component was significantly suppressed in the case of the exploding box stimulus, whereas the N2c showed an enhancement for the burning box stimulus. This result highlights the impact of multisensory integration on the performance of realistic BCI applications. Indeed, we observed alterations in the offline classification accuracy for a detection task based on a mixed feature extraction (variance, power spectral density, and discrete wavelet transform) and a support vector machine classifier. In the case of the explosion, the accuracy slightly decreased by –1.64% p. in an audio-visual experiment compared to the visual-only. Contrarily, the classification accuracy for the burning box increased by 5.58% p. when additional auditory cues were present. Hence, we conclude, that especially in challenging detection tasks, it is favorable to consider the potential of multisensory integration when BCIs are supposed to operate under (multimodal) real-world conditions

Microwire crossbar arrays for chemical, mechanical, and thermal stimulation of cells

Over the past two decades, miniaturized biophysical tools, referred to as lab-on-a-chip or micro-total-analysis-systems, have become a vivid field of interdisciplinary research. This development is owed to the fact that these tools promise lower sample and time consumption and higher parallelization than classical wet-lab experiments. At the same time, these tools can offer a resolution that is often impossible to achieve with classical probe-based techniques. In this context, the present thesis investigates the use of microwire crossbar arrays to deliver chemical, mechanical, and thermal stimuli to networks of biological cells. The first part of this work considers magnetic microparticles as transducers of chemical and mechanical stimuli. To this end, a chipbased approach to exert precise control over these particles is examined. Here, microwire crossbar arrays are used as miniaturized electromagnets to generate highly localized magnetic fields. These fields, in turn, are used to exert precise control over the particles at subcellular resolution. In order to ensure successful delivery of the particles, simple but efficient protocols for the transport of particles are investigated. In the application of these protocols, a new approach to deploy and control individual particles on-chip is introduced. This method effectively [...

On-chip electromagnetic tweezers – 3-dimensional particle actuation using microwire crossbar arrays

Emerging miniaturization technologies for biological and bioengineering applications require precise control over position and actuation of microparticles. While many of these applications call for high-throughput approaches, common tools for particle manipulation, such as magnetic or optical tweezers, suffer from low parallelizability. To address this issue, we introduce a chip-based platform that enables flexible three-dimensional control over individual magnetic microparticles. Our system relies on microwire crossbar arrays for simultaneous generation of magnetic and dielectric forces, which actuate the particles along highly localized traps. We demonstrate the precise spatiotemporal control of individual particles by tracing complex trajectories in three dimensions and investigate the forces that can be generated along different axes. Furthermore, we show that our approach for particle actuation can be parallelized by simultaneously controlling the position and movement of 16 particles in parallel

Voltage-controlled stimulation of HL-1 cells with nanocavity arrays

Multielectrode arrays (MEA) have been widely used for the analysis of intercellular communication in cellular networks and pharmacological studies. Generally they are used for the recording of action potentials but have also been applied in the detection of neurotransmitter release. They allow for non-invasive multi-channel measurements and high-throughput screening. Crucial parameters for the performance of on-chip electrical stimulation and recording are the electrode impedance, sealingresistance between the cell and the electrode, and electrode size and density. These factors determine the noise level, leakage currents, necessary stimulation voltages/currents, and the spatial resolution of the system. The improvement of the electrode-cell interface has gathered great attention in the last years. Nanocavity arrays provide large electrode areas combined with a small aperture to access the reservoir above the electrode and therefore allow for low impedance and highly localized measurements. MEA-based extracellular action potential recordings and electrical stimulation of electrogenic cells are well established. Based on a formerly published method, we now present a simplified fabrication protocol for designing nanocavity arrays, which is independent of CMOS technology. This method allows for flexible and easy modification of standard MEAs to improve their electrode characteristics. We combine the advantages in electrode impedance and spatial resolution of these devices with voltage-controlled stimulation of a cardiomyocyte-like cell line (HL-1). We induce propagating action potential waves, to show the possibility of pacing cardiac tissue with the nanocavity arrays. The high-jacking of the network’s pacemaker and the influence on action potential propagation and frequency by stimulation are demonstrated and illustrated using a cross-correlation analysis of calcium imaging sequences

Microwire crossbar arrays for on-chip localized thermal lesion of cell cultures

Driven by an advance in microfabrication technologies, the development of miniaturized analytical platforms has become a major interest in physical, chemical, and biological research over the past two decades. On one hand, these systems offer the possibility to massively decrease the amount of resources and time necessary for current point-of-care medical diagnostics. On the other hand, the possibility to interact with biological systems in a highly controlled and easily parallelizable manner offers many promising opportunities for fundamental biological and biophysical research. For example, when studying the healing process of complex tissues after lesion, the use of simplified in vitro models can help to elucidate basic mechanisms. In this context, a means to create these lesions with high spatial control and resolution is of great importance. While the use of lasers coupled to microscopes is capable of delivering the necessary control and resolution, the requirement of external optics renders an application to on-chip devices difficult. Here, we demonstrate the use of microwire crossbar chips for the generation of localized thermally induced lesions in on-chip tissue models. Our chips consist of two orthogonal layers of parallel microwires, insulated from the culture medium by a polyimide layer. Cardiomyocyte-like HL-1 cells are cultured on the chip as an in vitro tissue model. Passing an electrical current through a given set of microwires leads to thermal heating of the active wires, which consequently imposes a localized stress on the cells cultured at the chip’s surface. We demonstrate that using this method, complex lesion patterns with a resolution in the lower micrometer regime can be created. The success of the lesion as well as the effects on the surrounding cells are evaluated using Calcein/EtHD staining methods. We further analyze the distinct Ca2+ propagation inside the cell layer revealing partially decoupled network activity depending on the applied lesion patterns. In conclusion, we believe that our method can be used as a versatile tool to study tissue lesions in simplified model systems. As a chip-based method, it also allows for low-cost production, as well as straight-forward inclusion in microsystems, which facilitates high-throughput and the generation of statistically relevant data from biological systems prone to high noise levels

On-chip 3-dimensional control of microparticles for lab-on-a-chip applications

Functionalized magnetic beads have become a versatile tool for labeling, actuation and trapping of biological cells and molecules. In order to conduct in-depth studies of individual cells and cellular networks efficient tools to handle these beads with micrometer resolution or below are necessary. We present the combined application of magnetic and dielectrophoretic forces generated by microwire crossbar arrays. This allows for precise three-dimensional control over the position of single micrometer-sized beads. The crossbar arrays are produced by standard photolithographical methods and can thus be implemented into lab-on-a-chip systems in a straight-forward manner

Nanostructured cavity devices for extracellular stimulation of HL-1 cells

Microelectrode arrays (MEAs) are state-of-the-art devices for extracellular recording and stimulation on biological tissue. Furthermore, they are a relevant tool for the development of biomedical applications like retina, cochlear and motor prostheses, cardiac pacemakers and drug screening. Hence, research on functional cell-sensor interfaces, as well as the development of new surface structures and modifications for improved electrode characteristics, is a vivid and well established field. However, combining single-cell resolution with sufficient signal coupling remains challenging due to poor cell-electrode sealing. Furthermore, electrodes with diameters below 20 µm often suffer from a high electrical impedance affecting the noise during voltage recordings. In this study, we report on a nanocavity sensor array for voltage-controlled stimulation and extracellular action potential recordings on cellular networks. Nanocavity devices combine the advantages of low-impedance electrodes with small cell-chip interfaces, preserving a high spatial resolution for recording and stimulation. A reservoir between opening aperture and electrode is provided, allowing the cell to access the structure for a tight cell-sensor sealing. We present the well-controlled fabrication process and the effect of cavity formation and electrode patterning on the sensor's impedance. Further, we demonstrate reliable voltage-controlled stimulation using nanostructured cavity devices by capturing the pacemaker of an HL-1 cell network

Inducing microscopic thermal lesions for the dissection of functional cell networks on a chip

We present a versatile chip-based method to inflict microscopic lesions on cellular networks or tissue models. Our approach relies on resistive heating of microstructured conductors to impose highly localized thermal stress on specific regions of a cell network. We show that networks can be precisely dissected into individual subnetworks using a microwire crossbar array. To this end, we pattern a network of actively beating cardiomyocyte-like cells into smaller subunits by inflicting thermal damage along selected wires of the array. We then investigate the activity and functional connectivity of the individual subnetworks using a Ca2+ imaging-based signal propagation analysis. Our results demonstrate the efficient separation of func- tional activity between individual subnetworks on a microscopic level. We believe that the presented tech- nique may become a powerful tool for investigating lesion and regeneration models in cellular networks