OPTICAL COHERENCE ELASTOGRAPHIC AND TOMOGRAPHIC MICROSCOPY FOR RESOLUTION-ENHANCED MICROMECHANICAL AND STRUCTURAL IMAGING OF BIOLOGICAL SYSTEMS

376 pagesSupplemental file(s) description: Chapter 6 Supplementary Movie 3, Chapter 6 Supplementary Movie 2, Chapter 6 Supplementary Movie 1, Chapter 2 Supplementary Movie 1.Optical microscopy has had a revolutionary impact in the biomedical sciences. Among other modalities, optical coherence tomography (OCT) offers a unique capability for label-free structural imaging of biological systems at cellular resolution over millimeter-scale volumetric field-of-view. The rapidly growing field of mechanobiology has presented immense opportunities for not only structural microscopy, but also functional imaging of biomechanical properties with emerging optical elastography techniques. Importantly, attention has been given to the role of biomechanical interactions between cells and the extracellular matrix (ECM) in various biological processes, including onset and progression of cancer, stem cell differentiation, morphogenesis, and wound healing. Although a suite of techniques is available for both biochemical and biophysical characterization of the cells, techniques for mechanical characterization of the ECM are still typically limited to surface micro-indentation via atomic force microscopy (AFM) or bulk mechanical testing. This drives the need for new imaging tools to probe spatially-resolved micromechanical properties of the ECM at the cellular scale in the physiologically relevant 3D environments. Indeed, the enhancement of spatial resolution has been an ongoing pursuit in all fields of imaging. The first portion of this dissertation presents the development and demonstrations of photonic force optical coherence elastography (PF-OCE), a new optical elastography technique to enable quantitative 3D micromechanical microscopy of biopolymer constructs and engineered cellular systems. PF-OCE utilizes long-range optical micromanipulation with radiation pressure from a weakly-focused laser beam to achieve an ‘AFM-like’ localized “pushing” of micro-beads embedded and distributed in 3D space within the sample. The second portion of this dissertation addresses fundamental questions related to the factors that limit spatial resolution and approaches for resolution enhancement in both elastography and optical coherent imaging. As a whole, this dissertation contributes technological advances in the field of optical elastography that offer new imaging capabilities to support future mechanobiological research endeavors as well as new perspectives and implications related to the fundamental imaging science of spatial resolution in both elastography and optical coherent imaging