Date of Graduation

12-2015

Document Type

Thesis

Degree Name

Master of Science in Biomedical Engineering (MSBME)

Degree Level

Graduate

Department

Biomedical Engineering

Advisor/Mentor

Kartik Balachandran

Committee Member

Timothy Muldoon

Second Committee Member

Jeffrey Wolchok

Keywords

Applied sciences, Aortic valve, Cell geometry, Cell phenotype, Stress calculations, Valve interstitial cells

Abstract

The aortic valve is a highly dynamic structure responding to actively to the chemical, mechanical and physical cues of the valve microenvironment. Valve interstitial cells are dispersed throughout the valve tissue and play an important role in maintaining the integrity and optimum function of the valve. They are a heterogeneous population composed of various phenotype. These phenotypes have specific functions characteristic of valve physiological and pathological conditions. The effect of mechanical loading and chemical modulators on the behavior of the valve interstitial cells have largely been studied. However the role of valve interstitial cell shape as an intrinsic physical cue on cell behavior has not been considered yet. Based on the actively responsive nature of the valve interstitial cells and the evidence of the relationship between cellular shape and behavior for the other types of cells, we decided to investigate the effects of valve interstitial cells shape on the contractile function and phenotype modulation. Various cell shapes were designed by constraining the cells into different line/pattern widths (10µm, 20µm, 40µm, 60µm, and 80µm) using soft lithographic techniques. Cells were aligned into the lines exhibiting varied cytoskeletal organizations. Orientation of the actin filaments significantly decreased with increasing the pattern width. A similar trend was observed for the cell aspect ratio and nuclear eccentricity. Contractile function of the cells was examined utilizing a custom valavular thin film assay. All the films of the tissue construct responded to the vasoconstrictive and vasodilatory drugs. Cellular maximum contraction did not reveal any specific trend while cell basal tone had some statistical variations showing the maximum value for 40µm in which cell-cell contact and cell elongation may have interacted optimally. Analysis of the contractile and activated phenotype markers was performed using western blot on vimentin, α-smooth muscle actin and smooth muscle myosin heavy chain. The expression of these proteins did not change significantly for the patterns suggesting that the cell contractility may be more correlated to the cell shape than phenotype. In conclusion we were able to modulate valve interstitial cellular shape using soft lithographic techniques and cause alterations in cellular function. Cell phenotype may not be a regulating factor of the cell behavior as commonly measured.

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