The effect of substrate surface topology on the interaction of living cells with inanimate substrates is a well-established phenomenon. When cells are placed on biomaterials, they outgrow protrusions called filopodia that sense surface features in their immediate surroundings and initiate the formation of stable cell adhesion complexes closer to the cell body. Adhesion proteins permit filopodia to constantly explore the surrounding microenvironment. A better understanding of the relationship of filopodia with surface features is highly relevant for exploiting custom-made surfaces to guide cell activity. In this work, mathematical modeling and simulation were used to describe different phenomena related to the interaction of a filopodium with its microenvironment, with the aim of reproducing experimentally observed phenomena associated to filopodia growth and interactions with substrates. The Kelvin Voigt model was used for the viscoelastic response of filopodia. Result predict filopodia protrusion under test conditions and helps improving our understanding on the effect of substrate topology on the biomechanical response of filopodial extensions.

I. The function, structure and response to environmental factors of a cytoplasmic protrusion found in rat leukemia cells IRC 741 were investigated. A greater rigidity and adhesiveness of the protrusions, as compared to the main cell body, was demonstrated by time-lapse cinematography, and this functional difference was correlated with localized ultrastructural differences in the cytoplasm and on the cell surface, and with higher negative surface-charge density, as shown by cell electrophoresis. The formation or maintenance of the cytoplasmic protrusions depended on adequate nutritional conditions, and was interfered with by diminished intercellular contact, by environmental temperatures below 37°C, by alkaline pH and by calcium-ion depletion. The protrusion appears to represent a type of adhesive organelle not previously described in either cancer cells or normal cells. II. In the course of the above work, a method was developed whereby the differential staining of viable and nonviable unfixed cells, as observed by the dye-exclusion method, can be reproduced in glutaraldehyde-fixed preparations by staining with alcian blue. The results suggest that the differential staining is due, at least in part, to structural differences that are retained following aldehyde-fixation. / Science, Faculty of / Zoology, Department of / Graduate

In the mammalian seminiferous epithelium, the cytoplasm of Sertoli cells adjacent to sites of intercellular attachment exhibits unique structural attributes. In each of these regions, a layer of hexagonally packed actin filaments lies situated between a cistern of endoplasmic reticulum and the plasma membrane. The filament layer together with the reticulum and adjacent plasma membrane are collectively termed an "ectoplasmic specialization". Ectoplasmic specializations occur in apical Sertoli cell regions at sites of attachment to spermatids and basally at sites of attachment to adjacent Sertoli cells. Ectoplasmic specializations have been hypothesized to be actin associated intercellular adhesion junctions. If this is true, molecular components that characterize actin associated adhesion junctions in general should be present in ectoplasmic specializations. In this study, I tested this prediction in two ways. First, I investigated whether or not the protein vinculin is co-distributed with actin filament bundles in ectoplasmic specializations of the ground squirrel. Second, I immunologically probed ectoplasmic specializations for three cell adhesion molecules (CAMs) that are commonly found in regions of intercellular adhesion in other tissues. My results indicate that vinculin is co-distributed with actin in Sertoli cell regions attached to spermatids. These data are consistent with the conclusion that vinculin is a component of ectoplasmic specializations and, therefore, with the hypothesis that the latter structures are a form of actin associated adhesion junction. Experiments using probes for the CAMs indicate that E-cadherin, A-CAM and N-CAM are probably not present in ectoplasmic specializations. The adhesion molecule at these sites may be a different member of the known CAMs or an as yet unidentified CAM. Based on data presented here and elsewhere indicating that ectoplasmic specializations are a form of actin associated adhesion junction, I describe the elaborate changes that occur in constituent filament bundles at sites of attachment to spermatids of the ground squirrel and interprete them in the context of the adhesion hypothesis. During the course of the co-localization studies described above, I observed that vinculin and actin are co-distributed at certain sites of intercellular attachment between interstitial cells of Leydig in the ground squirrel testis. Moreover, at the ultrastructural level I found these sites correspond to microfilament rich junction regions. These observations are consistent with the conclusion that actin associated intercellular adhesion junctions exist between interstitial cells of Leydig in the ground squirrel testis. / Medicine, Faculty of / Graduate

Acidiphilium cryptum is a heterotrophic acidophile commonly found in acidic environments and industrial bioleaching operations. Attachment to mineral surfaces may serve to maintain this organism in aqueous environments where it is subject to removal by hydrodynamic forces. Using indirect and direct methods we have looked at the binding of A.cryptum to chalcopyrite (CuFeS₂) and other mineral ores to determine whether specific adhesins mediate binding. A modified ELISA binding assay (the Ore ELISA) was developed to measure direct adherence. Finely ground chalcopyrite was bound irreversibly to the walls of an ELISA plate, the organisms were added and after incubation and washing, the number of attached bacteria were assessed by reacting with anti-A.cryptum antibody followed by goat anti-rabbit IgG conjugated to alkaline phosphatase. This assay was found to be sensitive, rapid and reproducible. The Ore ELISA allowed direct binding measurement in the presence of various inhibitors and provided a rapid screening method for adherence-defective mutants. Adherence was shown to be saturable and increased slightly as pH decreased. A moderate increase in binding affinity was recorded in the presence of monovalent and divalent cations and EDTA. Various bactericidal agents and pentose and hexose sugars had no effect on chalcopyrite attachment. Reducing agents had little effect on cell adherence. A strong increase in adherence was observed in the presence of surface active agents. Bovine serum albumin and gelatin were both found to markedly reduce mineral surface binding. Competition for attachment sites between A.cryptum and the autotrophic acidophile, Thiobacillus ferrooxidans, showed that each organism binds to unique sites on the chalcopyrite surface. A.cryptum mutant strains displaying reduced adherence to chalcopyrite were shown to lack a 31.6 kDa outer membrane protein. / Science, Faculty of / Microbiology and Immunology, Department of / Graduate

No description available.

This thesis presents a simple force-based model of moving and interacting cells that incorporates a realistic description of cell adhesion and applies it to a system of spherical cells. In addition, several results in matrix theory are proved with the end of showing that the equations produced by the model uniquely determine the motion of the system or cells.

No description available.

Finite element models have been successfully used to analyze adhesive bonds in actual structures, but this takes a considerable amount of time and a high computational cost. The objective of this study is to develop a simple and cost-effective finite element model for adhesively bonded joints which could be used in industry. Stress and durability analyses of crack patch geometries are possible applications of this finite element model. For example, the lifetime of aging aircraft can be economically extended by the application of patches bonded over the flaws located in the wings or the fuselage. Special two and three- dimensional adhesive elements have been developed for stress and displacement analyses in adhesively bonded joints. Both the 2-D and 3-D elements are used to model the whole adhesive system: adherends and adhesive layer. In the 2-D elements, adherends are represented by Bernoulli beam elements with axial deformation and the adhesive layer by plane stress or plane strain elements. The nodes of the plane stress-strain elements that lie in the adherend-adhesive interface are rigidly linked with the nodes of the beam elements. The 3-D elements consist of shell elements that represent the adherends and solid brick elements to model the adhesive. This technique results in smaller models with faster convergence than ordinary finite element models. The resulting mesh can represent arbitrary geometries of the adhesive layer and include cracks. Since large displacements are often observed in adhesively bonded joints, geometric nonlinearity is modeled. 2-D and 3-D stress analyses of single lap joints are presented. Important 3-D effects can be appreciated. Fracture mechanics parameters are computed for both cases. A stress analysis of a crack patch geometry is presented. A numerical simulation of the debonding of the patch is also included. / Ph. D.

N cadherin is one member of the cadherin superfamily. It like other classes of cell adhesion molecules (CAMs and FAKs) is responsible for cell-cell adhesion ... specifically during early morphogenesis. · N cadherin is the designated cell adhesion molecule for neural tissue. It, in concert with several signal transduction pathways, allows an early neurite to follow chemical and adhesive gradients from its origin to its destination. N cadherin can only operate as an affector of neurite or growth cone guidance when in complex. As a mediator of information from the outside environment to the inside cytoskeleton, N cadherin must rely on cooperation with PTPµ ( a protein tyrosine phosphatase), ~ and a catenin to make firm connection with actin. With that connection established, an early growth cone can make decisions based on chemical and adhesive cues. Movement of the growth cone, as a function of adhesion or "homophilic binding," is termed "haptotaxis." Intracellular concentrations of catenin pools and the activity of two pathways (Src and Wnt) regulate the entire system. Based on studies and experimental data, a model, with respect to complex orientation and behavior is proposed.

Peritoneal adhesions occur in up to 93% of adults after peritoneal trauma during surgery. Most adhesions are asymptomatic but can cause female infertility, small bowel obstruction (SBO) and chronic abdominal pain. Adhesion prophylaxis is needed to reduce the significant morbidity and increased health care costs resulting from peritoneal adhesions. This thesis aims to establish a relevant and reproducible experimental adhesion model to simultaneously study the healing processs and adhesion formation and later to examine whether carbazate-activated polyvinyl alcohol (PVAC), an aldehyde-carbonyl scavenger, can reduce adhesion formation or not; and, in a long-term follow-up, to investigate the incidence of and identify risk factors for adhesive SBO requiring surgical treatment after laparotomy during infancy and to survey the prevalence of self-reported chronic abdominal pain and female infertility. Male Sprague-Dawley rats were subjected to laparotomy, cecal abrasion, and construction of a small bowel anastomosis and examined at various time points after surgery. Early elevation of IL-6, IL-1β and TNF-α concentrations in peritoneal fluid but not in plasma correlate to adhesion formation in this rodent adhesion model, indicating that anti-adhesion treatment should be early, local and not systemic. The animals were treated with either peritoneal instillation of PVAC, or the anastomosis was sutured with PVAC-impregnated resorbable polyglactin sutures. At day 7, bursting pressure of the anastomosis was measured and adhesions were blindly evaluated using Kennedy- and Nair scoring systems. PVAC-impregnated sutures reduced adhesion formation without reducing bursting pressure. Infants who underwent laparotomy between 1976 and 2011 were identified (n=1185) and 898 patients were included with a median follow-up time of 14.7 (range 0.0-36.0) years. The median age at first laparotomy was 6 (range 1.0-365.0) days. There were 113 patients (12.6%) with adhesive SBO, with the highest incidence found in patients with Hirschsprung’s disease (19 of 65, 29%), malrotation (13 of 45, 29%), intestinal atresia (11 of 40, 28%) and necrotizing enterocolitis (16 of 64, 25%). Lengthy duration of surgery (hazard ratio (HR) 1.25, 95% CI, 1.07 to 1.45), stoma formation (HR 1.72, 1.15 to 2.56) and postoperative complications (HR 1.81, 1.12 to 2.92) were independent risk factors. Chronic abdominal pain was reported in 180 (24.0%) of 750 patients, and 17 (13.8%) of 123 women reported infertility. The morbidity after laparotomy in neonates and infants is high. Awareness of the risk factors may promote changes in surgical practice.