Date of Award

Fall 2019

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical & Aerospace Engineering

Program/Concentration

Mechanical Engineering

Committee Director

Venkat Maruthamuthu

Committee Member

Moustafa Maoustafa

Committee Member

Shizhi Qian

Committee Member

Oleksandr Kravchenko

Abstract

Physical characteristics of the microenvironment, such as geometry and stiffness, influence cell adhesion and contractile forces. Here, we determined how these physical factors influenced cell force exertion and adhesion in two specific contexts that have broad relevance.

Fibroblasts are cells in connective tissues that interact with a fibrous extracellular matrix (ECM) that have a predominantly one-dimensional (1D) (fibrillar) geometry. However, it has been unclear as to how the 1D nature of the fibrillar ECM influences the forces exerted by fibroblasts. Here, we used fibroblast cells adherent on fibronectin lines on polyacrylamide (PAA) gels of stiffness 13 and 45 kPa to restrict the cells in a 1D geometry. We used traction force microscopy (TFM) to quantify fibrillar force exertion by fibroblasts. We found that, even though the cell length depended on substrate stiffness, the exerted force was independent of it. Furthermore, we found that fibrillar fibroblasts display prominent linear actin structures. Accordingly, we found that the cell length and forces exerted by fibroblasts highly depend on the actin nucleator formin. These findings have important implications for disease conditions such as fibrosis.

In epithelial tissues, epithelial cells adhere to the ECM and to neighboring cells to maintain tissue architecture. E-cadherin adhesions bind neighboring cells together, but whether these adhesions respond to surrounding cell-like stiffness is unknown. Here, we developed a biomimetic interface with oriented immobilization E-cadherin with cell-like stiffness to mimic cell-cell binding. We fabricated soft silicones with stiffness in the range of that of epithelial cells (0.4 – 8.7 kPa) (as quantified using rheology) for this purpose. We found that the single cells on stiffer substrates tend to form prominent linear adhesions whereas those on softer substrates are more likely to form just nascent adhesions. The presence of contractile circumferential actin appears to be important for large adhesion formation. We also found that the formation of large E-cadherin adhesions highly depends on the actin nucleator formin, but not Arp2/3. Our biomimetic E-cadherin substrates have thus enabled us to gain insights into the effect of cell-like stiffness on E-cadherin adhesion, which is relevant to understand morphogenesis as well as cancer.

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DOI

10.25777/f20y-xh23

ISBN

9781392699928

ORCID

0000-0003-0430-1663

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