Date of Award

9-2009

Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Polymer Science and Engineering

First Advisor

Alfred J. Crosby

Second Advisor

Patricia Wadsworth

Third Advisor

Harry Bermudez

Subject Categories

Materials Science and Engineering

Abstract

The relationship between cells and their environment is one of dynamic reciprocity, whereby cells can influence their surrounding and the surroundings can influence the cells. One example of this relationship arises from the effect of the mechanical properties of an environment on a cell and of a cell on its environment. Inspired by this relationship, we investigate 1) the local environment of biological materials, both native and synthetic, and 2) the forces that cell sheets exert on surfaces. We do this by developing techniques that focus on local mechanical properties and experimental strategies that provide insight into intercellular mechanics. We first focus on determining local mechanical properties of hydrogel materials by developing the Cavitation Rheology technique. This process involves inducing a cavitation event at the tip of a syringe needle. We develop theory to show that the critical pressure to cavitate can be directly related to the modulus of the material (Chapter 2). This allows us to experimentally determine the mechanical properties at arbitrary locations throughout a material scaffold over a range of length scales defined by the needle radius (Chapter 3). We then demonstrate that we can viturally elminate the energy contribution from the creation of new surface area to the critical pressure by cavitating with a media of lower surface energy (Chapter 4). In chapter 5, we show that Cavitation Rheology can be used on native biological tissues and we go on to demonstrate the importance of measuring the mechanical properties in vivo. We then focus on understanding the force development of cells as they grow to confluency on a dynamic substrate (Chapter 6). We demonstrate the method of living microlenses to measure the collective strains cell sheets attain by growing cells on a thin polystyrene film supported by a surface of microwells. The cells cause the film to buckle and the resultant buckling can be directly related to the strain. We use this technique to study the strains exerted by various cell types and to determine the importance of the cell-cell junctions on the strain development.

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