http://hdl.handle.net/2268.2/2004 Thu, 14 May 2026 16:41:48 GMT 2026-05-14T16:41:48Z http://hdl.handle.net/2268.2/25186 Title: Master thesis : Design and development of non-contact electrodes electrooculogram acquisition system for sleep measurements Abstract: Physiological signal monitoring plays an important role in the assessment of sleep quality and the diagnosis of sleep disorders such as sleep apnea. During sleep, eye movements provide valuable information about sleep stages, especially during rapid eye movement (REM) sleep. The electrooculogram (EOG) is commonly used in sleep studies to detect eye movements and to support sleep-stage classification. However, conventional EOG acquisition systems rely on wet or dry contact electrodes placed near the eyes which can be uncomfortable, restrictive and poorly tolerated during overnight or long-term measurements. These limitations motivate the development of alternative acquisition techniques that improve comfort and ease of use while maintaining sufficient signal quality. This work presents the design, development and experimental validation of a non-contact electrooculogram (EOG) acquisition system. It is intended for easy-to-use, comfortable by reducing skin irritation and wearable physiological monitoring, making them more suitable for overnight and repeated measurements. Non-contact electrodes measure biopotential signals through a thin insulating layer, such as fabric. However, they also introduce very high electrode–skin impedance and increased sensitivity to environmental noise, especially power-line interference. The system was first modeled and analyzed using LTSpice simulations to understand the impact of modified skin–electrode interface of non-contact electrode. A dedicated PCB was designed and implemented, integrating an analog front-end with impedance buffers in the non-contact electrodes and amplification stages, filtering and grounding strategies in the main board. The design is made versatile to allow for the use of wet, dry or non-contact electrodes, adjustable gains and filters to study their impact on signal quality. After troubleshooting, a repeatable measurement protocol was defined with timed eye-movement phases to ensure consistent comparison between experimental runs. Experimental recordings were performed using fully non-contact recording electrodes and a grounded reference electrode. The output signal was acquired with an oscilloscope and post processed by a Python code. This code is dedicated to plot the output but can also apply digital 50 Hz notch filtering, compute the signal-to-noise ratio (SNR), apply the Fast Fourier Transform (FFT) over the signal. The results show that the system is able to detect typical eye activities such as left and right movements, blinking and random eye movements. Despite these encouraging results, the measurements remain strongly affected by power-line interference and by experimental factors such as reference electrode coupling, skin moisture, electrode pressure, and environmental conditions. Overall, this work demonstrates the feasibility of non-contact EOG acquisition as a proof of concept for sleep monitoring applications. Thu, 22 Jan 2026 23:00:00 GMT http://hdl.handle.net/2268.2/25186 2026-01-22T23:00:00Z http://hdl.handle.net/2268.2/24912 Title: Master thesis : Clarifying the Neuronal and Neurovascular Properties of the fMRI Global Signal Amplitude During Mind-Blanking Reports Abstract: Mind-blanking, a state where individuals report an absence of thought, has been associated with slow-wave electroencephalogram (EEG) activity and increased functional magnetic resonance imaging (fMRI) global signal amplitude (GSA). However, the specific contributions to GSA during this state remain unclear. The objective of this study is to identify and clarify the specific components of the fMRI global signal during mind-blanking. Understanding how these components contribute to the phenomenon can shed light on the underlying neural and physiological mechanisms driving this state. We analysed the data collected from the simultaneous EEG–fMRI. Participants performed the Sustained Attention to Response Task and were asked to report their mental state and level of alertness throughout the experiment. We extracted fMRI GSA, EEG oscillatory amplitudes, and heart rate variability derived from electrocardiogram (ECG) from these data. Then, linear mixed-effects models were used to examine how these measures relate to GSA across mind-blanking, mind-wandering, and on-task conditions. Our findings showed that when individuals reported mind-blanking episodes, the global signal amplitude was significantly negatively linked to delta and theta EEG activity, and moderately positively linked to physiological factors, particularly heart rate variability. Across all states, GSA correlated positively with theta and negatively with alpha oscillations. In summary, the observed increase in the global signal amplitude appears to be primarily driven by physiological changes, which can provide insights that mind blanking is not a purely neuronal process and can be associated with increased heart rate activity as well. Sun, 07 Sep 2025 22:00:00 GMT http://hdl.handle.net/2268.2/24912 2025-09-07T22:00:00Z http://hdl.handle.net/2268.2/24903 Title: Bioprinting of GelMA - Phycocyanin hydrogels for chondrogenic differentiation Abstract: Osteoarthritis (OA) is a common and severe joint disease characterized by disruption of the inflammatory process, leading to degradation of cartilage and surrounding tissues. Its onset is still not completely understood, and current treatments are not only limited but also potentially harmful due to severe adverse effects (e.g., infections or renal toxicity). Among the consequences of OA, the dedifferentiation of chondrocytes - the sole cell type in cartilage - is of particular concern, as the loss of their native phenotype further aggravates cartilage damage. One potential strategy to address this issue is the use of hydrogels. Their 3D structure can mimic the native cartilage environment and influence both cell differentiation and regenerative cascades. In addition, phycocyanin (PC), a photosynthetic pigment and protein widely consumed as a food supplement, has demonstrated strong anti-inflammatory effects as well as other beneficial properties, including applications in tissue engineering. This study investigates the effects of PC in an inflammatory model composed of IL-1β (1ng/mL) and TNF-α (25ng/mL), designed to simulate OA pathophysiology. It also evaluates the ability of PC to promote chondrocyte redifferentiation when incorporated into gelatin methacryloyl (GelMA), a promising biomaterial, to create a novel bioink. PC toxicity was assessed at concentrations up to 200 μg/mL using Alamar Blue and CCK-8 assays, with no significant effect on cell growth. In a 2D culture model, PC reduced inflammation in stimulated chondrocytes, as shown by decreased Nf-κB staining, although qPCR results were less conclusive. The bioink was then prepared by mixing PC (100 μg/mL) with 10% GelMA, the standard working concentration in the group. Hydrogel constructs showed comparable viability to GelMA-only controls, while gene expression analysis revealed complex patterns related to chondrocyte maturation. Finally, printability tests indicated that viability was largely preserved, although a cluster effect (numerous chondrocyte aggregates) was observed. In conclusion, this work represents a first step toward developing a biofunctional material with potential to advance cartilage tissue engineering, by supporting chondrocyte redifferentiation, as well as OA modeling. Sun, 07 Sep 2025 22:00:00 GMT http://hdl.handle.net/2268.2/24903 2025-09-07T22:00:00Z http://hdl.handle.net/2268.2/24855 Title: N/A Abstract: Ce travail vise à étudier l’influence réciproque de la fatigue mentale et physique sur la performance. Il se base sur une mesure de l’activité neuromusculaire grâce à l’électromyographie de surface. La fatigue est définie comme un état psychophysiologique dynamique qui affecte les processus cognitifs, physiologiques et comportementaux. Elle agit sur la performance, la sécurité et la santé dans l’ensemble des domaines de la vie courante. A travers une revue bibliographique, ce mémoire explore les mécanismes communs de la fatigue mentale et physique, notamment leurs bases neuronales, leurs marqueurs physiologiques et leurs composantes perceptives. De nombreuses études tendent à indiquer que les performances physiques peuvent être altérées par la fatigue mentale en lien avec une augmentation de la perception de l’effort plutôt qu’en limitant directement la capacité musculaire. Réciproquement, la fatigue physique peut affecter les performances cognitives, indiquant une interdépendance entre ces mécanismes. Cette recherche analyse la fatigue neuromusculaire en s’appuyant sur des résultats expérimentaux. Durant le protocole expérimental, les participants sont soumis à des conditions de tâche simple et double, avec induction de fatigue cognitive et/ou physique. Les mesures sont prises à l’aide de l’électromyographie spectrale. L’étude se concentre sur les résultats des participants ayant eu pour une tâche simple physique, afin de pouvoir comparer les effets de la tâche double sur les performances physiques. L’analyse conjointe de leur spectre et de leur amplitude (JASA) permet de distinguer la fatigue d’autres états physiques potentiels. Cette association permet de distinguer différents mécanismes de fatigue. Si l’amplitude augmente et la fréquence diminue, on parle d'un état de fatigue. Les résultats obtenus n’indiquent pas d’influence significative de la fatigue cognitive sur les performances physiques. Des techniques avancées s’inspirant de JASA ont aussi été appliquées afin d’améliorer l’analyse, mais, bien que prometteuses, celles-ci n’ont pas apporté de réponses plus significatives. Tout en contribuant à une meilleure compréhension de la fatigue, ce travail met en évidence la nécessité de protocoles d’évaluation combinant mesures subjectives, comportementales et physiologiques. Sun, 07 Sep 2025 22:00:00 GMT http://hdl.handle.net/2268.2/24855 2025-09-07T22:00:00Z