BioMed Theses

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    The effect of air atmosphere casting and oxidation on the properties, crystallinity and biodegradability of novel Zn-3cu-0.3bi
    (Wichita State University, 2023-12) Jaraba, Khulud; Mahapatro, Anil
    The terms biodegradable, bioresorbable, and bio-absorbable, are used interchangeably in literature to describe the ability of a material to degrade in the biological environment. Nonetheless, the definitions of these three terms differ. Biodegradable materials have a natural capability to gradually and safely degrade when in direct contact with a biological organism whereas bioresorbable and bio-absorbable materials are materials that organically decompose and get absorbed by surrounding tissue [1]. In recent years and with the aging of the population, the need for biodegradable implants increase since they eliminate the complications associated with the prolonged presence of inert metallic implants and the need for an implant removal operation [2]. However, there have been many concerns associated with the use of biodegradable metals in the applications of stents and fixation devices, such as unsuitable degradation rate, loss of mechanical integrity, and increased metal ion concentrations. The performance of biomaterials in-vivo is highly correlated to the fabrication environment and technique which is an overlooked area of research Therefore, the objective of this thesis is to investigate the impact of alloy casting atmosphere and methods on the properties, crystallinity, and biodegradability of Zn-3Cu-0.3Bi. To achieve that, different casting methods were examined. The effect of metal melt oxidation and borax flux usage was investigated to help evaluate the efficiency of flux assisted air casting technique. The results suggest that the use of borax flux minimizes metals’ oxidation, increases materials’ crystallinity, reduces crystallite size, and produces more homogenous alloys. Furthermore, the ternary zinc alloy system fabricated showed superior hardness than pure zinc and achieved a uniform degradation with a corrosion rate within the design requirement for cardiovascular and fixation implants.
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    Using machine learning to predict f-actin morphology of endothelial cells: An application for mechanobiology models
    (Wichita State University, 2023-05) Hafenstine, Rex W.; Long, David S.
    The expansive monolayer of cells in direct contact with blood is called the endothelium. The endothelium is fundamentally involved with almost every human disease. The endothelium is composed of endothelial cells (EC)s that exhibit structural and phenotypical heterogeneity that vary in time and space. These cells exhibit emergent properties that allow communication with neighboring cells. Since experimental observation of ECs at a single cell level will not provide complete details on these behaviors, other techniques are needed. One method for observing these emergent properties is through 3D dynamic response of cell shape and morphology. Live-cell imaging is limited, such as the number of structures or events that can be imaged. Therefore, incorporating a complementary method such as machine learning (ML) could be a feasible option. To validate if ML could predict 3D f-actin fibers from only the cell membrane, human dermal microvascular endothelial cells were grown to confluence, the cell membrane, nucleus, and f-actin were fluorescently labeled, and imaged with confocal microscopy. The images were processed via normalization techniques, segmented, augmented, and filtered before being introduced into a conditional generative adversarial network (cGAN). The f-actin predictions from the cGAN did not perform at a level previously seen when predicting 3D nucleus and focal adhesion (FA) structures. However, these results do not necessarily mean that the f-actin fibers cannot be predicted but may require different methods, such as tuning the cGAN parameters (batch size and additional learning rates), obtaining more raw images, or testing different deep learning (DL) algorithms. Future work should also include testing a primary cell line of human dermal blood endothelial cells to minimize cell overgrowth, transfecting the cell with a K-Ras CAAX motif to improve cell membrane labeling, and developing new image similarity metrics to compare the predicted f-actin images with their corresponding ground truth images.
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    A bluetooth-enabled, light weight, flexible epidermal electronic system for ECG monitoring
    (Wichita State University, 2022-12) Chowdhury, Rakhi; Lee, Yongkuk
    With 17.9 million deaths annually, cardiovascular diseases (CVDs) have become the leading cause of mortality worldwide. This increased death rate creates a significant need for long-term ambulatory ECG monitoring for early diagnosis and treatment. Commercially existing ECG monitors use rigid materials, aggressive adhesives, and lack mechanical compliance with skin. Here, a wireless, Bluetooth-enabled, flexible, low-profile epidermal ECG monitoring device is presented with high-quality ECG signals. Electrode placements with different distances are investigated to find the optimal placement position of the electrode on the chest for identical readings with traditional ECG lead I and II. Afterward, the dry electrode and circuit are microfabricated using 2 $\mu{m}$-thick copper foil. The functionality of the electrode is demonstrated with stretchability, contact impedance, and EMG SNR measurement. The device's functionality is presented with a flexibility test, antenna performance test, RSSI measurement, and ECG signal collection. Contact impedance values for gel and dry electrodes are comparable, which are 3.94 and 3.96, respectively. Also, EMG SNR values are comparable for gel and dry electrodes, with 18.12 dB and 17.84 dB, respectively. Mechanical and electrical experiments suggest a 2 mm radius of curvature at 180° bending as the maximum flexibility of the device and a 30m long working distance for constant wireless communication between the device and a portable device. The morphology and quality of ECG signals acquired from human subjects during different activities demonstrate the device's potential for ambulatory monitoring. Overall, our findings prove the device is flexible, Bluetooth enabled, and can provide conformal contact with skin to achieve ECG monitoring in real-time effortlessly. Future work should include validating the device's functionality with data collection during different activities of the human subject.
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    Characterization of an RF resonator to measure fluid volume for biomedical applications
    (Wichita State University, 2022-12) Arafah, Suhaib Amjad; Cluff, Kim
    Wearable technologies have gained a huge interest in recent years due its advantages in the early diagnosis of medical conditions such as heart attack and monitoring intercranial pressure. Additionally, wearable technologies are an attractive solution in the medical field due to wearable form factor and minimal required training for uses. As such, in this study we are investigating a wearable RF skin patch resonator for the measurement of fluid volume changes. Specifically, this study aims to characterize the sensitivity, dynamic range, and repeatability of the sensor response to changes in fluid volume. The wearable skin patch sensor is an open circuit resonator that is energized wirelessly via an external antenna placed within closed proximity. Once the resonator is energized via the external antenna, it develops its own electromagnetic field and measure the changes in fluid volume nearby. For this study, we used a vector network analyzer for the purpose of energizing the wearable sensor and collecting the $S_{11}$ return loss. From the VNA, we measure the resonance frequency shift in terms of frequency in MHz and amplitude in dB. In this study, the characterizations of the skin patch sensitivity and dynamic range were performed by dynamically increasing the fluid $(H_{2}0)$ volume inside a chamber and collecting the sensor response. The result of this study illustrates that the larger square planner resonators has higher dynamic range than the others sensor designs such as triangle, circle, and pentagon while measuring fluid volume changes up to 540 mL. Furthermore, the sensitivity of large square skin patch resonator was greater than 0.75 mL. In this study, we are able to characterize the sensitivity and dynamic range of the wearable skin patch sensor which will lead into future advancement and development.
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    Inkjet printing techniques for wearable/stretchable electronics in healthcare
    (Wichita State University, 2022-12) Al Wahid, Ali Mohammed; Lee, Yongkuk
    Inkjet printing techniques, a good alternative of the traditional MEMS techniques, can be utilized to fabricate flexible and stretchable electronics, which can be used for healthcare applications. Therefore, the objectives of this study are 1) Providing proof of concept for the inkjet printing parameters for silver (Ag) and polyimide (PI) inks, 2) understanding the relationship between the dynamics of inkjet-printed patterns and surface energies of the substrate, and 3) demonstrating printing a flexible circuit on a PI coated substrate. During experiments, the effects of the printing parameters including jetting voltages, cartridge temperatures, and drop spacings of both the Ag and PI inks via the drop size and line width measurements were explored. The surface energies were manipulated by applying $O_2$ and $CF_4$ plasma for different durations using Reactive Ion Etching (RIE) that were measured by the means of contact angle measurements and ink drop size and line width measurements. Our results indicated that 1) the drop sizes increase as jetting voltages and cartridge temperatures increase, respectively, 2) the line widths decrease with increasing drop spacings, and 3) the $CF_4$ plasma increases the hydrophobicity of the surface while $O_2$ increases the hydrophilicity of the surface. Collectively, we successfully demonstrated accurate printing of multi-layered ECG circuit with a drop size of 40 $\mu{m}$ for the Ag ink and PI ink. The next goal will be to demonstrate wireless continuous monitoring of reliable ECG signals using the printed ECG circuit.