abstract / Mechanical Engineering / Doctoral / Doctor of Philosophy

Surfaces with nanopatterned biological functionality are important prerequisites for many applications including developing biosensors, tissue engineering scaffolds and Bio-MEMS devices. This work presents a versatile technique, termed nanoscale orthogonal biofunctionalization imprint lithography, which allows "top-down" highprecision nanopatterning of proteins that can meet the demands of various applications. To show applicability of this technique, it was used to create disposable large scale arrays of nanopatterned cell adhesion proteins for cell culture for the purpose of investigating the influence of nanoscale geometrical parameters on cell-surface interactions. These cell culture arrays were used to systematically vary the size, spacing and density of fibronectin adhesion clusters, which are expected to modulate the signaling induced by the cell adhesion, the clustering of adhesion molecules and the force generated in the cytoskeleton. As a result, it was first determined that the nanopatterned adhesion sites provided an upper limit to the size of a corresponding cell focal adhesion. Cell morphology, actin stress fibers, vinculin distribution, proliferation and motility were all influenced by nanoscale fibronectin island size, and in some cases, the distance between patterns. Several parameters depended biphasically on the pattern size, indicating a very fine regulation of the associated cell signaling. Adhesion area and local stress on the adhesion are modulated by the adhesion size, and the cell response on the nanopattern shows strong parallels to the response on elastic adhesion substrates. In addition, chemical signaling may be influenced directly by changing the activity of associated enzymes. The results of this work build a basis for an understanding of adhesion on the nanoscale level and offer design criteria for the engineering of biomaterials and tissue scaffolds.

Current biomaterials are designed to be passive in nature to prevent the initiation of adverse immune responses upon contact with biological substances. While this approach of inertness is still a crucial design component for some applications, the possibility of engineering desired cell responses in the local environment of the material exists and is of particular interest in implantable devices and tissue engineered constructs. Fundamental knowledge of the relationships between cell adhesion and gross cell behavior will provide key design criteria for the creation of advanced biomaterials that induced locally controlled cellular responses. This work investigates the possibility of engineering cell behavior by limiting adhesion site maturation. Chemically-defined nanoislands of fibronectin were created using a combination of nanosphere lithography and an orthogonal surface functionalization strategy. Investigation of the adhesive and cytoskeletal components of cells cultured on these surfaces demonstrates that chemically-defined nanopatterns provide an upper size limit to adhesion site growth which in turn influences the degree of cytoskeletal formation. The imposed restriction on adhesion site growth results in the formation of a relatively higher number of more evenly distributed, small adhesions throughout the cell body. The adhesive behavior can be tuned by changing the nanopattern properties with respect to their size, spacing, and density. Furthermore, it is demonstrated that the observed differences in cell adhesion as imposed by the nanopatterned surfaces induces changes in gross cell behavior with respect to spreading, proliferation, and motility. The results presented here parallel observations documented in cells cultured on elastic surfaces and indicate that intracellular signaling cascades initiated and governed by cellular adhesion sites are sensitive to adhesion size/maturation and possibly the amount of force generated locally at these adhesion sites. The conclusions drawn from these studies give insight into the possibility of implementing nanostructured biomaterials for cell engineering purposes and provide design criteria for the next generation of tissue engineered constructs. / text

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Polymer organosilicate nanocomposites have attracted significant attention over the last decade due to improved mechanical, thermal, and barrier properties. Several nanocomposite researchers have recognised potential for biomedical applications, however none have conducted biological investigations. In this project, the predicted ability of the organosilicate to enhance biostability, modulate the release of included drugs, and confer biofunctionality and control over the host response, were assessed as the three primary hypotheses. The studies were conducted with the objective being employment as urinary device biomaterials. Of prime importance was that no detrimental change in cytocompatibility was resultant. Biomedical thermoplastic elastomeric polyurethane organosilicate nanocomposites were prepared from poly(ether)urethane of 1000g/mol poly(tetramethylene oxide) polyol, 4,4??? diphenylmethane diisocyanate, and 1,4 butanediol chain extender chemistry, and various organosilicates with loadings from 1w% to 15w%, using a solution casting technique. Initially, partially exfoliated nanocomposites were produced using a commercially available organosilicate, Cloisite?? 30B. These nanocomposites displayed several advantageous properties, namely i) significant anti-bacterial activity, reducing S. epidermidis adherence after 24h to ~20% for a 15w% organosilicate loading, ii) enhanced biostability, with a 15w% organosilicate loading displaying only slight degradation after a 6 week subcutaneous in vivo ovine implantation, and iii) static modulation of model drug release as a factor of drug properties and organosilicate loading. The former was attributed to the Cloisite?? 30B quaternary ammonium compound, while the latter two were likely primarily barrier effect related and due to changes to poly(ether)urethane permeability. Electrostatic and chemical interactivity between drug and organosilicate was also implicated in the observed drug release modulation. Unfortunately, a lack of in vitro cytocompatibility and poor in vivo inflammatory response will limit in vivo use. Utilising bioinert 1-aminoundecanoic acid as an alternative organic modification, cytocompatible intercalated nanocomposites were produced thus likely allowing in vivo nanocomposite use and exploitation of the barrier effect related properties. However, these nanocomposites were not antibacterial. Variation of the organic modification and/or use of co-modification were viable means of modulating host response and biofunctionality, however nanoscale dispersion of co-modified silicate was poor. Use of nanocomposite technology was concluded beneficial to existing biomaterials, and specifically to biomaterial application as urinary catheters / stents.

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

Thesis (M.D.S.) - Department of Oral Pathology and Oral Surgery, University of Adelaide, 1982. / Typescript (photocopy).

Thesis (Ph.D.)--University of Nebraska-Lincoln, 2008. / Title from title screen (site viewed Oct. 31, 2008). PDF text: x, 336 p. : ill. (chiefly col.) ; 6 Mb. UMI publication number: AAT 3309211. Includes bibliographical references. Also available in microfilm and microfiche formats.

Thesis (Master)--İzmir Institute of Technology, İzmir, 2005. / Keywords: Hydroxyapatite, bioceramics, biomaterials. Includes bibliographical references (leaves.78-80).

Thesis (Master)--İzmir Institute of Technology, İzmir, 2004 / Includes bibliographical references (leaves. 95).