Optimization of Fabrication Conditions and Calibration of Polyvinylidene Fluoride for use as a Biosensor
2022-08
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Optimization of Fabrication Conditions and Calibration of Polyvinylidene Fluoride for use as a Biosensor
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2022-08
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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.
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University of Minnesota M.S.Ch.E. thesis.August 2022. Major: Chemical Engineering. Advisor: Victor Lai. 1 computer file (PDF); v, 36 pages.
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Danley, Matthew. (2022). Optimization of Fabrication Conditions and Calibration of Polyvinylidene Fluoride for use as a Biosensor. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/243051.
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