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ÖgeTuneable carbon nanotube-based sensors for a textile-integrated respiratory system(Graduate School, 2024-08-12) Arslan, Dilan ; Sezer, Esma ; Cebeci, Hülya ; 509211285 ; ChemistryConventional medical respiratory devices, such as spirometers and airflow meters, are commonly used for monitoring respiratory signals and assessing patients' health. However, these devices require complex setups typically used in hospitals or clinical settings. Furthermore, these devices' large and bulky structures can cause patients discomfort. Additionally, measurements conducted using such devices are often intermittent, which leads to gaps in providing a complete and continuous picture of a patient's respiratory health. In response to these challenges, there is an increasing demand for patient-centered and cost-effective solutions in next-generation healthcare systems. These systems are designed to enhance patient comfort and enable continuous monitoring and evaluation of essential health metrics such as respiratory function in the home or daily life settings. Wearable technology development and widespread adoption have become a significant priority in this context. This thesis investigates the potential of sustainable and cost-effective carbon nanotubes (CNTs) and cellulose nanocrystals (CNCs)-based conductive ink production, as well as the optimization and characterization of production parameters to address the abovementioned needs. The thesis also explores the sensory behavior of wearable sensors designed to monitor respiratory signals with different geometries, including line, strain gauge, and omnidirectional patterns. Additionally, the study examines the performance of sensors using a simulation mannequin. The comprehensive analysis aims to advance the development of user-friendly and economical wearable respiratory monitoring devices that can enhance patient care and provide accurate data for healthcare professionals. In the first chapter, an overview of the thesis was presented, providing a broad context for the research and outlining the primary objectives and scope of the study. The second chapter comprises a comprehensive literature review, examining existing research and studies pertinent to the thesis topic and elucidating the current knowledge in the field. In the third chapter, firstly, five different inks were produced by varying the ratio of CNTs and CNCs as follows: CNTs:CNCs-1:1, CNTs:CNCs-1.5:1.5, CNTs:CNCs-2:2, CNTs:CNCs-2:1, and CNTs:CNCs-1:2. The rheological behavior of these water-based conductive inks with different concentrations was examined aiming to determine the inks' viscosity, flow, and spread properties. The time-dependent stability of the inks and simulation tests of the screen printing method were performed using a rheological approach. Secondly, screen printing, an accessible and cost-effective method, created sensory surfaces on fabric. Optic microscope and scanning electron microscope (SEM) images of the printed sensors were taken to understand the print quality of the surface. Then, the electrical resistances and conductivities of the printed surfaces were measured. Thirdly, the electromechanical properties of the produced respiratory sensors were examined using a specially designed test setup. 5% and 10% strains were applied to the line, strain gauge, and omnidirectional patterns to simulate the human chest. Electrical resistance values were recorded simultaneously from the sensor surfaces, and the sensor's sensitivity was calculated. Finally, tests were conducted on a humanoid mannequin to determine the suitability of a wearable sensor for practical use. The results of these tests were compared with the data obtained from the electromechanical tests to evaluate the selected pattern's suitability for the intended application. In the fourth chapter, the results of the mentioned characterization were demonstrated and discussed. The results indicated that all inks exhibited shear-thinning behavior, making them suitable for screen printing. The recovery rates of the inks were calculated, revealing that the ink with the best recovery rate was CNTs:CNCs-1:1, with approximately 100%. It was determined that CNTs:CNCs-2:1 and CNTs:CNCs-1:2 were unsuitable for printing on fabric using the screen printing method, and it concluded that the inks suitable for the screen printing method were CNTs:CNCs-1:1, CNTs:CNCs-1.5:1.5, and CNTs:CNCs-2:2. The inks maintained their stability throughout the testing period, i.e., five months. Moreover, the electrical conductivity and stability of the patterns demonstrated their suitability for the intended applications. The electrical resistance of the inks decreased as the number of layers increased due to closing gaps in the print and forming an electrical network. Also, it was found that as the amount of CNT in the ink increased, the sensor's reproducibility decreased. Therefore, the optimal ink was determined to be CNTs:CNCs-1:1. Furthermore, while the line pattern exhibited high sensitivity values, its reproducibility was low. The omnidirectional pattern was found to be the most optimal, as it provided better stress distribution due to its multiple arms. Tests performed on a humanoid mannequin supported this conclusion. The fifth chapter comprehensively discussed the conclusions and recommendations for further investigation. It highlights the most significant findings and their implications and encourages ongoing exploration in this field, potentially leading to new insights and advancements. The study's findings indicate that these CNTs/CNCs-based inks are well-suited for screen printing. This can potentially facilitate the development of user-friendly and cost-effective wearable respiratory monitoring devices. Such devices can enhance patients' quality of life and enable healthcare professionals to make more informed clinical decisions by providing more accurate and comprehensive respiratory data. The widespread use of wearable technologies in the healthcare industry will offer significant advantages for patients and healthcare professionals. Furthermore, this study's results will significantly contribute to the existing literature on developing and applying respiratory monitoring devices.