Characterization of Spongelike Porous Polyvinylidene Fluoride (PVDF) for use as a Biosensor

Abstract

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.