Longitudinal imaging of a 3D model of calcific aortic valve disease, which consisted of co-cultured GFP+ Valve Endothelial Cells (VEC) and Valve Interstitial Cells (VIC), was performed with a combined Optical Coherence Microscopy (OCM), confocal reflectance and fluorescence microscopy system. The acquired confocal volumes depicted the VEC morphological changes and migration as well as collagen fiber alignment. With the aid of computational refocusing and multi-volume processing, the OCM datasets could visualize VIC cell bodies, matrix remodeling, nodule formation and calcific deposits. The complementary information derived using this combined approach could help unravel the cellular mechanisms leading to aortic valve calcification.
A combined 1300 nm Optical Coherence Microscopy (OCM) and 488 nm confocal reflectance/ fluorescence microscopy system was designed to perform high-resolution, high-specificity imaging of collagen-embedded spheroids. Spheroids of Hyaluronic Acid (HA) synthase-overexpressing breast epithelial cells alone, or co-cultured with adipose stromal cells were imaged. The volumes, acquired either after fixing and staining or longitudinally with labeling, enabled the visualization of the spheroid morphology, luminal structures, cellular organization, and collagen matrix remodeling. The morphology and internal lumen structures of spheroids, as large as 500 μm in diameter, could be obtained from the OCM volumes, even in the presence of dense collagen matrix surrounding the spheroids. The confocal stacks provided superior specificity to discriminate cells from the compacted collagen along the spheroid’s periphery, up to a depth of ~120 μm. The combined use of OCM and confocal imaging on these spheroid models has added to our understanding of how HA may contribute to tumor initiation and invasion.
We demonstrate a single-shot full-field reflection-mode off-axis quantitative phase microscopy with temporal focusing. The new imaging system is capable of achieving diffraction-limited optical sectioning quantitative phase imaging without any spatial or angular multiplexing. It has high potential to achieve ultrafast imaging with camera-limited frame rate. We show that the QPM can measure the depth-dependent intracellular scattering dynamics of cells and reveals 3D structure of tissues with different phenotypes at sub-cellular resolution.
We present an acoustic-driven quantitative phase microscope for quantifying cell biomechanics at sub-cellular level. Longitudinal acoustic standing wave is established as mechanical loadings to deform cells. A reflection quantitative phase microscopy with high axial and lateral resolution is used to quantify the cell deformations. We evaluate cancerous and normal cells undergoing standing wave modulation, where both the time-lapse cell membrane fluctuations and whole-cell volumetric shape changes are measured. Our technique can achieve high throughput, label-free and non-invasive quantification of cell mechanics with high mechanical sensitivity over broad mechanical frequency response range and can potentially be extended to study 3D tissue mechanics with sub-cellular resolution.
We demonstrate applications of photonic-force optical coherence elastography (PF-OCE) on imaging three-dimensional (3D) micro-scale mechanical heterogeneity in collagen phantoms and cell-modified extracellular matrix. In collagen, we observed strong correlations between the measured mechanical heterogeneity and local OCT intensity in the vicinity of beads, which could be related to the presence of fibrous structures. Moreover, we quantitatively imaged micro-scale localized stiffening and increased heterogeneities in fibers surrounding an isolated NIH-3T3 fibroblast enclosed in a 2.5 mg/mL fibrin gel with a volumetric field-of-view (FOV) of ~80μm×350μm×50μm. Our results show that PF-OCE is able to characterize 3D micromechanical properties of biomaterials, and has the potential to observe dynamics of cell-ECM interactions.
Photonic force optical coherence elastography (PF-OCE) is a new approach for volumetric characterization of microscopic mechanical properties of soft materials. PF-OCE utilizes harmonically modulated optical radiation pressure to exert localized mechanical excitation on individual microbeads embedded in viscoelastic media. We present microrheological quantification of complex shear modulus in polyacrylamide gels with PF OCE. Spectroscopic measurements over a frequency range spanning 1 Hz to 7 kHz revealed rich frequency-dependent microstructural dynamics of entangled polymer networks across multiple microrheological regimes. PF-OCE provides an all-optical approach to quantitative three-dimensional mechanical microscopy and broadband spectroscopic microrheological studies of soft materials.
Pulsed photothermal interferometry (PTI) gas sensor with hollow-core photonic bandgap fibre (HC-PBF) is demonstrated with a Sagnac interferometer-based phase detection system. Under the condition of constant peak pump power, the optimal pulse duration is found to be > 1:2 μs for detecting low-concentration of trace gases in nitrogen, limited by thermal conduction of gases within the hollow-core. Preliminary experiments with a 0.62-mlong HC-PBF gas cell, low peak power ( ~ 20:2mW) and a boxcar averager with 10k average times demonstrated a detection limit of 3:3 p:p:m acetylene. Detection limit down to ppb or lower is expected with high peak power pump pulses.
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