Doctor of Philosophy, University of Akron, 0, Biomedical Engineering

The tricuspid valve, which is located on the right side of the heart, prevents blood backflow from the right ventricle to the right atrium. Regurgitation in this valve occurs when its leaflets do not close normally. Tricuspid valve regurgitation is one of the most common tricuspid valve dysfunctions, often requiring valve repair or replacement. The long-term success rate of the repair surgeries has not been promising; in many cases, reoperations are required within a few years after the first surgery. A limiting factor in understanding the etiology of tricuspid valve repair failure is our lack of knowledge regarding tricuspid valve biomechanics. In particular, tricuspid valve mechanical behavior has not been accurately studied. In addition, there is no precise analytical and/or computerized model to predict the mechanical responses of the valve under normal and pathological conditions. In the current study, we have used biaxial tensile testing, small angle light scattering, ex-vivo passive heart beating simulation, and sonomicrometry techniques to quantify the mechanical characteristics, microstructure, dynamic deformations, and geometric parameters of the tricuspid valve. We aimed to develop a more accurate computerized model of the tricuspid valve for simulation purposes. Our studies are important both for understanding the normal valvular function as well as for development/improvement of surgical procedures and medical devices.

Committee: Rouzbeh Amini Dr. (Advisor); Brian Davis Dr. (Committee Member); Ge Zhang Dr. (Committee Member); Francis Loth Dr. (Committee Member); Rolando Ramirez Dr. (Committee Member) Subjects: Anatomy and Physiology; Biomechanics; Biomedical Engineering; Biomedical Research; Engineering; Surgery; Technology

Doctor of Philosophy, The Ohio State University, 2016, Biomedical Engineering

Volume overload (VO) induced heart failure results from an increase in blood volume (preload) to the heart. The heart responds to increases in hemodynamic load through compensative remodeling. VO has a distinct pattern of remodeling compared to pressure overload induced heart failure, which results in fibrosis. VO results in a net decrease in extracellular matrix (ECM). This loss of ECM contributes to the progression of the disease due to the loss of structural integrity. Since cardiac fibroblasts (CFs) are the main cells responsible for maintaining ECM in the heart, we characterized the in vitro phenotype of CFs isolated from a rat VO model, aortocaval fistula (ACF). Compared to sham operated animals, ACF fibroblasts displayed a phenotype that we described as “hypofibrotic”. ACF CFs secreted relatively less collagen and profibrotic molecules, such as a-smooth muscle actin (aSMA) and connective tissue growth factor (CTGF). Interestingly, ACFs produce approximately twice as much transforming growth factor-ß1 (TGF-ß), a key profibrotic stimulus, as their sham counterparts. However, there were no changes in the canonical TGF-ß pathway that could account for the hypofibrotic phenotype observed in ACF fibroblasts. Since others have shown that the cytoskeleton and the Rho/ROCK pathway play a role in fibroblast phenotype, we characterized the actin cytoskeleton in sham and ACF fibroblasts. We found that ACF CFs have significantly less F-actin than sham CFs. We were able to show that it is possible the actin cytoskeleton might account for phenotypic differences in CFs by chemically altering the amounts of F-actin and G-actin. When the cells were treated with a ROCK inhibitor, which allows F-actin to depolymerize into G-actin, CFs displayed a more hypofibrotic phenotype. Conversely, enhancement of F-actin with jasplakinolide treatment forced the CFs to have a profibrotic phenotype. Numerous studies have linked substrate modulus with effects on the cytoskeleton. S (open full item for complete abstract)

Committee: Keith Gooch PhD (Advisor); Jun Liu PhD (Committee Member); Pamela Lucchesi PhD (Committee Member); Aaron Trask PhD (Committee Member) Subjects: Biomedical Engineering