Combinatorial techniques have changed the paradigm of materials research by allowing a faster data acquisition in complex problems with multidimensional parameter space. The focus of this thesis is to demonstrate biomaterials design and characterization via preparation of two dimensional combinatorial libraries with chemically-distinct structured patterns. These are prepared from blends of biodegradable polymers using thickness and temperature gradient techniques. The desired pattern in the library is chemically-distinct cell adhesive versus non-adhesive micro domains that improve library performance compared to previous implementations that had modest chemical differences. Improving adhesive contrast should minimize the competing effects of chemistry versus physical structure. To accomplish this, a method of blending and crosslinking cell adhesive poly(季aprolactone) (PCL) with cell non-adhesive poly(ethylene glycol) (PEG) was developed. We examine the interaction between MC3T3-E1 osteoblast cells and PCL-PEG libraries of thousands of distinct chemistries, microstructures, and roughnesses. These results show that cells grown on such patterned biomaterial are sensitive to the physical distribution and phases of the PCL and PEG domains. We conclude that the cells adhered and spread on PCL regions mixed with PEG-crosslinked non-crystalline phases. Tentatively, we attribute this behavior to enhanced physical, as well as chemical, contrast between crystalline PCL and non-crystalline PEG.

Cardiovascular disease is the main cause of death in the United States. Many of these conditions require the grafting or bypassing of compromised blood vessels. To this effect, biological vascular grafts (autografts and allografts) are the first line of action. However, when the patient lacks vasculature suitable for grafting use, several synthetic grafting options are available. The search for an inert biomaterial for vascular grafts has proven to be unsuccessful. This makes the interaction taking place on the blood-biomaterial interface critical for the success of the grafts. This thesis introduces a new bio-inspired approach to tackle the mechanical and biological challenges of vascular material design. The hypothesis of this research is that recombinant fibronectin protein can be stably incorporated onto elastin-mimetic polymers to increase endothelialization. Recombinant elastin, designed to recreate the mechanical properties of natural elastin as a candidate material for vascular graft fabrication, was used as a model surface. Recombinant fibronectin-functionalized elastin-mimetic polymer displayed significant improvement in cell adhesion. Quantification of surface bound recombinant fibronectin verified the concentration dependence of this cell adhesive behavior. Modified elastin-mimetic polymer also demonstrated an enhanced ability to support endothelial cell proliferation. Furthermore, the stability of recombinant fibronectin-modified polymers was assessed. These studies provide the foundation for fabricating elastin-mimetic vascular grafts with improved endothelialization and subsequent biological performance.

Cell adhesion plays an important role in inflammation and immunological responses. Adhesion molecules (e.g., selectins and integrins) are key modulators in mediating these cellular responses, such as leukocyte trafficking under shear stress. In this thesis, we use a bio-membrane force probe (BFP) to study force regulation on kinetics and conformations of selectin and LFA-1 integrin. A new BFP was built up, and a new assay, using thermal fluctuation of the BFP, was developed and used to monitoring selectins and their ligands association and dissociations. The new BFP was also used to investigate the force and force history dependence of selectin-ligand interactions. We found tri-phasic transition of force-dependent off-rates and force-history dependence of selectin/ligaind interactions. The BFP was also used to characterize force-dependent lifetimes of the LFA-1-ICAM-1 interaction. We found that LFA-1/ICAM-1 bonds behaved as catch bond and that LFA-1-ICAM-1's catch bonds were abolished blocking the downward movement of αA domain α7 helix. Finally, the BFP was applied to dynamically probe the global conformational changes of LFA-1 and to characterize force-regulated transitions among different conformational states on a living cell. We observed dynamic transitions of LFA-1 between extended and bent conformations on living cells. The observed average distance change of LFA-1's extensions was about 18nm, while that of the bending was only about 14nm. We also found that forces could facilitate extension but they slow down the bending of LFA-1. The observed transition time of extension was less than 0.1s, while that of contraction was longer than 0.2s. Our observations here are the first in-situ evidence to demonstrate how integrins dynamically transit different conformations and how force regulates these transitions.

The colonization of immersed surfaces by a myriad of marine organisms is a complex, multi-stage, species-specific process giving rise to economic and environmental costs. This unwanted accumulation of organisms in the marine environment, called biofouling, has been attacked from different fronts, going from the ‘problem-elimination-as-problem-solving’ strategy (essentially through the use of biocides) to more elaborated and environmentally-friendly options based on the principle of ‘non-stick’ or ‘easy foul-release’ surfaces, which do not jeopardize marine life viability. Several marine organisms rely on proteinaceous adhesives to secure a holdfast to surfaces. Proteolytic enzymes have been demonstrated to be effective agents against settlement and settlement consolidation onto surfaces of marine bacteria, algae, and invertebrates, their proposed mode-of-action being the enzymatic degradation of the proteinaceous components of the adhesives. So far, however, the evidence remains inconclusive since most of the published investigations refer to commercial preparations where the enzyme is mixed with other components, like additives, which obviously act as additional experimental variables. This work aims at providing clear, conclusive evidence about the potential of serine proteases to target the adhesives produced by a group of model marine biofoulers. The strategy towards the goal consisted in the preparation and characterization of maleic anhydride copolymer nanocoatings modified by a surface-bound enzyme, Subtilisin A, the active constituent of the commercial preparations reported as effective against biofouling. The enzyme-containing maleic anhydride copolymer films were characterized (enzyme surface concentration, activity, stability, roughness and wettability) and thereafter tested in biological assays with three major biofoulers: spores of the green alga Ulva linza, cells of the pennate diatom Navicula perminuta, and cyprid larvae of the barnacle Balanus amphitrite. The purpose of the biological assays was to elucidate the efficacy of the immobilized catalyst to discourage settlement and/or to facilitate removal of these organisms from the bioactive layers. Results confirmed the initial hypotheses related to the enzymatic degradation of the biological adhesives: the immobilized protease was effective at reducing the adhesion strength of Ulva spores and Navicula diatoms in a manner that correlated with the enzyme activity and surface concentration, and deterred settlement of Balanus amphitrite barnacle cyprids even at the lowest surface activity tested. By facilitating the removal of biofilm-forming diatoms and of spores of the troublesome alga Ulva linza, as well as by interfering with the consolidation of adhesion of the calcareous Balanus amphitrite macrofouler, the enzyme-containing coatings here disclosed are considered to constitute an appealing and promising alternative to control marine biofouling without jeopardizing marine life.

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Modification of the surface chemistry of materials used as implants in biomedical applications affords the ability to control cell adhesion, prevent inflammation and enhance integration with the host. Titanium and its alloys are strong and lightweight thereby making them desirable for applications such as hip and knee replacements, dental implants, and cardiac pacemaker implants. However, the lifetime of these implants is often limited by poor incorporation into the surrounding bone which results in loosening and wear. In order to overcome these limitations we have studied the modification of titanium substrates with a self-assembled monolayer that can be used to perform surface-initiated atom transfer radical polymerization (SI-ATRP) of a monomer to afford polymer brushes that effectively prevent the adhesion of cells. In addition, the polymer brushes afford the ability to tether a peptide sequence. Specific peptides containing adhesion sequences have been tethered to the polymer brushes. The resulting surfaces promote cell adhesion and osteoblast differentiation, thereby increasing bone tissue formation around the implant resulting in better incorporation of the implant.

Thesis (Ph. D.)--University of Virginia, 2008. / Title from title page. Includes bibliographical references. Also available online through Digital Dissertations.

Thesis (Ph. D.) -- University of Texas Southwestern Medical Center at Dallas, 2005. / Vita. Bibliography: 108-115.