Living organisms are made up of a multitude of individual cells that are surrounded by biomolecules and fluids. It is well known that cells are highly regulated by biochemical signals; however it is now becoming clear that cells are also influenced by the mechanical forces and mechanical properties of the local microenvironment. Extracellular forces causing cellular deformation can originate from many sources, such as fluid shear stresses arising from interstitial or blood flow, mechanical stretching during breathing or compression during muscle contraction. Cells are able to sense variations in the mechanical properties (elasticity) of their microenvironment by actively probing their surroundings by utilizing specialized proteins that are involved in sensing and transmitting mechanical information. The actin cytoskeleton and myosin-II motor proteins form a contractile (actomyosin) network inside the cell that is connected to the extracellular microenvironment through focal adhesion and integrin sites. The transmission of internal actomyosin strain to the microenvironment via focal adhesion sites generates mechanical traction forces. Importantly, cells generate traction forces in response to extracellular forces and also to actively probe the elasticity of the microenvironment. Many studies have demonstrated that extracellular forces can lead to rapid cytoskeletal remodeling, focal adhesion regulation, and intracellular signalling which can alter traction force dynamics. As well, cell migration, proliferation and stem cell fate are regulated by the ability of cells to sense the elasticity of their microenvironment through the generation of traction forces. In vitro studies have largely explored the influence of substrate elasticity and extracellular forces in isolation, however, in vivo cells are exposed to both mechanical cues simultaneously and their combined effect remains largely unexplored. Therefore, a series of experiments were performed in which cells were subjected to controlled extracellular forces as on substrates of increasing elasticity. The cellular response was quantified by measuring the resulting traction force magnitude dynamics. Two cell types were shown to increase their traction forces in response to extracellular forces only on substrates of specific elasticities. Therefore, cellular traction forces are regulated by an ability to sense and integrate at least two pieces of mechanical information - elasticity and deformation. Finally, this ability is shown to be dependent on the microtubule network and regulators of myosin-II activity.

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No description available.

Collagen is one of the major protein constituents in mammals and is present in all tissues and organs with the exceptions of keratin tissues such as hair and nails. Collagen monomers self-aggregate into a number of structures. In order to understand the physical bases for the structural polymorphism observed in collagen, a good starting point is one of the simplest collagen aggregates, segmental long spacing (SLS) collagen. Although SLS collagen formation induced by the presence of adenosine 5’-triphosphate is widely known, effects of other triphosphates, on the other hand, are much less studied. By varying the pH, it is discovered that all the nucleoside 5’-triphophsates, as well as inorganic triphosphate, are able to induce SLS formation over certain pH ranges. Adenosine 5’-diphosphate and para-nitrophenylphosphate cannot induce SLS formation at any pH. Based on the pH ranges at which SLS collagen can be formed, it is concluded the triphosphate functionality, with one negative charge per phosphate group, is primarily responsible for the formation of SLS collagen. Since inorganic triphosphate is able to induce SLS collagen formation, the presence of the nucleoside is optional for the assembly process; however if present, the assembly process prefers the nucleosides carrying acidic protons. Using electron spectroscopic imaging (ESI) technique, it is found phosphorus, present only in nucleotides but not in polypeptides, is localized in certain regions of SLS collagen, forming a unique banding pattern transverse the long axis of the SLS collagen. Nitrogen mapping indicates the localization of phosphorus is not due to accumulation of materials. The phosphorus banding pattern demonstrates an excellent consistency across SLS collagen assembled from both bovine and recombinant human collagen monomers. Results from molecular simulation are consistent with the experimental results. All threephosphate groups seem to be involved in the assembly process to some degree. In the last chapter of the thesis, a reliable protocol to synthesis native type collagen fibers is introduced.

Collagen is one of the major protein constituents in mammals and is present in all tissues and organs with the exceptions of keratin tissues such as hair and nails. Collagen monomers self-aggregate into a number of structures. In order to understand the physical bases for the structural polymorphism observed in collagen, a good starting point is one of the simplest collagen aggregates, segmental long spacing (SLS) collagen. Although SLS collagen formation induced by the presence of adenosine 5’-triphosphate is widely known, effects of other triphosphates, on the other hand, are much less studied. By varying the pH, it is discovered that all the nucleoside 5’-triphophsates, as well as inorganic triphosphate, are able to induce SLS formation over certain pH ranges. Adenosine 5’-diphosphate and para-nitrophenylphosphate cannot induce SLS formation at any pH. Based on the pH ranges at which SLS collagen can be formed, it is concluded the triphosphate functionality, with one negative charge per phosphate group, is primarily responsible for the formation of SLS collagen. Since inorganic triphosphate is able to induce SLS collagen formation, the presence of the nucleoside is optional for the assembly process; however if present, the assembly process prefers the nucleosides carrying acidic protons. Using electron spectroscopic imaging (ESI) technique, it is found phosphorus, present only in nucleotides but not in polypeptides, is localized in certain regions of SLS collagen, forming a unique banding pattern transverse the long axis of the SLS collagen. Nitrogen mapping indicates the localization of phosphorus is not due to accumulation of materials. The phosphorus banding pattern demonstrates an excellent consistency across SLS collagen assembled from both bovine and recombinant human collagen monomers. Results from molecular simulation are consistent with the experimental results. All threephosphate groups seem to be involved in the assembly process to some degree. In the last chapter of the thesis, a reliable protocol to synthesis native type collagen fibers is introduced.

The research described covers fundamental studies of environmentally-responsive microgel-based thin films as a function of film architecture, microgel chemistry, film thickness, and environmental stimulus. Studies of multi-layer microgel thin films were conducted primarily using atomic force microscopy (AFM), quartz crystal microgravimetry (QCM), and surface plasmon resonance (SPR), each of which probed different aspects the film architecture as a function of pH of the environment around the film. Binary thin films were constructed by changing the ratios and composition of the microgels in solution to create multi-functional thin films for surface modification applications and were studied using AFM. The basic understanding of how these components create films at surfaces gives us insight into how the films perform and will allow for greater diversity without the guesswork. The morphology of films created from microgels with a degradable cross-linker was examined by AFM as a function of degradation of the particles structure. This thesis focuses mainly on very thin microgel films (<5 layers) studied using QCM, SPR, and AFM. Additional studies involving the characterization of semi-soft colloidal paint-on photonics are discussed in Appendix A.

Thesis (Ph.D.)--University of Melbourne, Dept. of Mathematics and Statistics, 2007. / Typescript. Includes bibliographical references (leaves 143-151).

Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.

Thesis (Ph.D.). / Written for the Dept. of Physics. Title from title page of PDF (viewed 2009/06/08). Includes bibliographical references.

Thesis (M.S.)--West Virginia University, 2004 / Title from document title page. Document formatted into pages; contains vi, 30 p. : ill. (some col.) Includes abstract. Includes bibliographical references (p. 29-30).