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Browsing by Author "Danley, Matthew"

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    Characterization of Spongelike Porous Polyvinylidene Fluoride (PVDF) for use as a Biosensor
    (2021-08) Danley, Matthew
    The Transcatheter Aortic Valve Replacement (TAVR) is a minimally invasive procedure that has grown in popularity in recent years, by using a catheter to deploy a replacement valve in patients with heart valve stenosis. Although minimally invasive, there are document complications, including a morality rate of 8.4% for TAVR procedures compared to 4.8% for tissue surgery procedures after 90 days for Medicare beneficiaries. It is proposed that the replacement valve alters blood flow and blood pressure after implantation and causes the complications. Instead of studying the changes in a living patient, creating a 3D printed model of the aortic tissue and studying the effects in-vitro is ideal, with a biosensor needed to detect these changes in blood flow and blood pressure. Polyvinylidene Fluoride (PVDF) is a piezoelectric polymer that is a promising material for the biosensor by generating different voltages in response to mechanical stresses such as compression forces. Porous PVDF samples have shown higher piezoelectric properties compared to nonporous membranes. It is thought that the increase in porosity allows the polymer chains to flex more and generate a larger piezoelectric output. Removing too much PVDF, however, negates any advantage of inducing pores, so there is an optimal porosity that will give the maximum piezoelectric output. The goal of this study is to find the optimal porosity of PVDF samples for use as a biosensor. By adding Zinc Oxide (ZnO) in various amounts to a solution of PVDF and 2-butanone during the fabrication process, and subsequently removing via an HCl acid bath once the 2-butanone was evaporated, porous PVDF sensors were made. The porosity of the PVDF samples were found using the gravimetric method. Fourier Transform Infrared (FTIR) spectroscopy was used to study the different polymer chain conformations, and to quantify the amount of piezoelectric chains in the PVDF sensors. There are three main chain conformations in PVDF, an α phase, β phase and γ phase. The β phase and γ phases are desired since they exhibit piezoelectric properties. The piezoelectric output of the PVDF sensors was quantified by calculating the d33 piezoelectric coefficient. By collecting the voltage generated from the sensors under different compressive loads. Results showed that the addition of ZnO nanoparticles to the PVDF sensors altered the porosity of the samples. As the amount of ZnO was increased during the fabrication process, the porosity of the PVDF sensors increased, which was expected. Changes in the amount of ZnO added during the fabrication process also led to statistically significant differences in the amount of piezoelectric chain conformations, but no trend or pattern with ZnO amount was observed. A trend emerged in which the piezoelectric properties increased as the amount of ZnO used during fabrication increased up to 30%wt ZnO, and then the piezoelectric output decreased at 40% and 50%wt ZnO, which is supported by literature. The d33 coefficient at 30%wt ZnO was found to be 1.8pC/N. Overall, the d33 coefficients increased as the amount of piezoelectric chain conformations increased in the sensors. This shows that the d33 values are dependent on the amount of piezoelectric chain conformations along with porosity. In summary, altering the amount of ZnO nanoparticles during the fabrication process led to changes in porosity and the amounts of piezoelectric chain conformations. Both factors affected the piezoelectric output of the sensors. Going forward, the fabrication process needs to be modified to control the amounts of piezoelectric chain conformations present in the PVDF samples which should increase the piezoelectric properties of the sensors.
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    Optimization of Fabrication Conditions and Calibration of Polyvinylidene Fluoride for use as a Biosensor
    (2022-08) Danley, Matthew
    The Transcatheter Aortic Valve Replacement (TAVR) is a minimally invasive procedure that utilizes a catheter to deploy a replacement valve in patients with valve stenosis. Although TAVR has lowered the risk of some complications, such as in-hospital mortality rates, there are documented increases in complications compared to open heart surgery, such as increasing numbers of pacemaker implantation after the procedure. The underlying mechanisms of these complications have not been identified. It is thought that 3D printing a replica of a patient’s aorta would allow for flow shear stress analysis, pressure compressive tests, and investigation of cyclic distension of the aortic walls. Polyvinylidene fluoride is a piezoelectric polymer that is a promising material to be used as a sensor to detect the shear stress, compressive forces, and distension inside the aorta model. Porous PVDF membranes have been shown to have higher piezoelectric properties compared to nonporous PVDF. It is thought the increase in porosity leads to a greater deformation, and in turn, a larger piezoelectric response to mechanical stresses. The goals of this study are to optimize the fabrication process of porous PVDF membranes using ZnO nanoparticles to induce pores and to design and build a flow chamber to then calibrate the PVDF membranes to physiological conditions. One issue identified in the fabrication process has been the removal of ZnO nanoparticles. The ZnO nanoparticles were added to a solution of PVDF and 2-butanone, cast and dried on a petri dish. 1cm by 1cm squares were cut from the PVDF membranes, weighed, and then placed in a hydrochloric acid bath. The HCl dissolved ZnO, which then diffused out of the membrane as ZnCl2. The mass of the membrane was measured at various time points while in the acid bath. These measurements were used to model the diffusion of ZnCl2 out of the membrane. The removal of ZnO was predicted to follow a shrinking core assumption, or a unimolecular diffusion of ZnCl2. The effective diffusivity of ZnCl2 was calculated for PVDF/ZnO membranes at 10%, 20%, 30%, and 40% wt ZnO as well as for 35-45nm, 80-200nm, and 500nm particle sizes. The effective diffusivities increased from 20% wt ZnO and peaked at 40% wt ZnO and decreased as the particle sizes increased from 35-45nm to 500nm. Further studying the porosity and tortuosity of PVDF membranes would allow for calculation of the diffusion coefficient of ZnCl2 out of the PVDF matrix. A flow chamber was built to calibrate PVDF membranes at physiological conditions in the aorta. 1” diameter tubing was used as the aorta segment and a submersible pump generate pressure and flow in the flow chamber. The voltages from the PVDF sensors were collected under varying flow rates (150mL/s – 400mL/s) and varying pressures (5mmHg to 30mmHg). The flow chamber mimicked the physiological flow rates of the aorta but did not mimic physiological pressure. The PVDF sensors generated decreasing signal as pressure and flow rates increased, which was not expected. Going forward, increasing the pressure in the flow chamber should allow for calibration of PVDF membranes under forces similar to those seen in the aorta.