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The interactions of microparticles, particularly those possessing nano- and microstructured asperities, play a critical role in many industrial applications. As a result, control over particle-particle and particle-surface interactions can be accomplished by designing microparticles with well-defined surface morphologies. Nature provides remarkable examples of evolutionary-optimized microscale biological particles with structures and/or chemistries tailored for effective adhesion to a variety of surfaces under different dynamic and environmental conditions. Prominent among these are pollen, which possess a range of ornamentations consisting of combinations of various morphologies and feature sizes. These surface structures, provided by a highly chemically and mechanically stable outer shell, make pollen a model bioparticle for evaluating geometric effects on adhesion. This research aims to take advantage of pollen's unique architecture by utilizing it as a biotemplate for designing pollen-derived particles with tailorable microparticle adhesion. In this work, the adhesion behavior of pollen and pollen-derived particles is characterized using atomic force microscopy (AFM). Cleaned natural pollen particles were found to exhibit short-range van der Waals (VDW) adhesion strengths that were independent of surface chemistry and scaled with the tip radius of pollen's ornamentations. Employing pollen as a core material, electrostatic interactions were utilized to controllably coat metal nanoparticles onto pollen's surface. Metal nanoparticle-coated pollen particles displayed enhanced adhesion facilitated by multiple nanoparticle contacts with probe surfaces, while also showing potential for use as surface enhanced Raman scattering (SERS) substrates. Using pollen as a template, a layer-by-layer (LbL) surface sol-gel (SSG) technique allowed for the preparation of high-fidelity ferro- and ferrimagnetic replicas exhibiting short-range VDW-based adhesion governed by the contact of nanocrystals present, and long-range magnetic attraction governed by the magnetic properties of ferrimagnetic pollen replicas. The results of this work highlight the feasibility of utilizing pollen as a bio-organic template and the potential for designing pollen-derived particles with tailorable adhesion.

No description available.

Cell-extracellular matrix and cell-cell adhesion are essential for biological processes such as cell motility, signaling, proliferation, cytoskeletal organization and gene expression. For this reason, extensive effort has been devoted in the past few decades to measure cell adhesion as well as identify key molecules involved. This thesis focuses on two outstanding problems in this area, namely, how to quantitatively characterize the adhesion between neural cells and the substrate and how to model the turnover of adhesions in the intriguing phenomenon of stretch-induced cell realignment. First of all, using a combined atomic force (AFM) and total internal reflection fluorescence microscope (TIRFM) system a novel method was developed to systematically and quantitatively examine the adhesion between neurite branches and the extracellular matrix. Specifically, a tipless AFM cantilever was used to penetrate between a well-developed neurite and the functionalized substrate and then gradually peel the neurite from the surface. At the same time, a laser TIRFM was utilized to monitor the activities of different adhesion molecules during the detaching process. This approach provides a solution to the long-standing problem of how to quantitatively measure neuron-extracellular matrix interactions while, simultaneously, identify the roles of various adhesion proteins in the process. Besides heathy neurons, testes have also been conducted on cells affected by the Alzheimer's disease (AD) where the influence of such disease on the mechanical response of neural cells was demonstrated. Secondly, to better understand the observed peeling response of the neurite, as well as extract key information from it, finite element (FEM) simulation was carried out using ABAQUS. It was shown that a good fit between the simulation results and experimental data can be achieved by representing the adhesion between two surfaces with simple cohesive interactions. In particular, it was found that the apparent adhesion energy density, a quantity of central interest in cell adhesion studies, is in the range of 0.2-0.8 mj/m^2. Last but not the least, a mechanochemical modeling framework was developed to investigate the mechanism of cell reorientation induced by cyclic stretching on the substrate. It was shown that the final alignment of cells reflects the competition between stress fiber assembly or disassembly, focal adhesion growth or disruption, substrate stiffening and whole-cell rotation. Predictions from the model are consistent with a variety of experimental observations, suggesting that the main physics of this intriguing phenomenon may have been well captured. / published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

Thesis (PhD)--University of South Australia, 1999

Thesis (PhD)--University of South Australia, 1999

Diss. (sammanfattning) Stockholm : Karol. inst. / Härtill 6 uppsatser.

Diss. (sammanfattning) Stockholm : Karol. inst. / Härtill 5 uppsatser.

Diss. (sammanfattning) Stockholm : Karol. inst. / Härtill 7 uppsatser.

Diss. (sammanfattning) Stockholm : Karol. inst. / Härtill 5 uppsatser.