Solid tumours are typically first diagnosed by palpation, revealing increased stiffness, while cancer cells are usually reported to be softer. The mechanical characteristics are not universal and depend on the cell type and the stage of development. Current techniques are usually point or 2D measurement techniques that lack depth penetration in 3D samples. We are developing optical coherence mechano-microscopy integrated with a confocal fluorescence microscope as a platform to investigate the mechanical phenotypes of 3D cancer models, mimicking the conditions in the native tumour microenvironment. This platform enables unique measurement of the 3D elasticity (i.e. Young’s modulus) of metastatic and non-metastatic breast cancer cell spheroids embedded in GelMAl, presenting the extracellular matrix, co-registered with fluorescence images. Our findings show that cells at the centre of non-metastatic cancer cell spheroids are softer (5.8 kPa) than the cells at the periphery (12.7 kPa). In contrast, migrating cells at the periphery of the metastatic cancer cell spheroids are softer (5.7 kPa) than the less motile cells at the centre of these spheroids (8.0 kPa).
Multicellular tumour spheroids have recently become important tools to investigate different stages of cancer development due to their 3D nature. We propose dynamic optical coherence microscopy (OCM) as a label-free low coherence interferometric technique for 3D characterization of morphology and cell motility during cell migration in multicellular cancer cell spheroids. We integrate dynamic OCM with confocal fluorescence microscopy (CFM) to validate and co-register the subcellular-scale endogenous contrast generated by dynamic OCM signal with sub-cellular features such as cell nucleus and membrane. We apply dynamic OCM integrated with CFM to scan metastatic and non-metastatic breast cancer cell spheroids embedded in gelatin-methacryloyl (GelMA) hydrogel and demonstrate that dynamic OCM provides high-contrast morphological imaging equivalent to that of confocal fluorescence in cancer cell spheroids. We use dynamic OCM to visualize different phases of cell migration such as invadopodia formation, cells breaking off from the primary tumour model, and migrating cells presenting a spindle-like shape, and to characterize cell motility at different stages.
Multicellular spheroids are a powerful model to study biochemical and biophysical interactions between cancer cells during growth and progression. However, little is known about how the biomechanics of the three-dimensional (3-D) microenvironment control cancer cell behaviors due to the lack of enabling technologies that can measure 3-D subcellular-scale elasticity and co-register it with the morphology and function of cells in a 3-D microenvironment. Here, we propose a multimodal imaging system that integrates an optical coherence microscopy-based subcellular mechano-microscopy system with a multi-channel confocal fluorescence microscopy system. Using this multimodal imaging system, we scan non-metastatic MCF7 breast cancer cell spheroids encapsulated in gelatin methacryloyl (GelMA) hydrogels and co-register 3-D intra-spheroid elasticity with subcellular structures, such as nuclei and cell membranes.
Mechanical properties of cells and extracellular matrix play important roles in the regulation of various biological processes such as gene expression, adhesion, and migration of cells. However, it is challenging to map three-dimensional (3D) elasticity on the micro-scale using existing techniques. We propose subcellular mechano-microscopy, a variant of compression-based optical coherence elastography, for 3D elastography of cell spheroids with isotropic elasticity resolution of 10 µm, over large fields of view covering multiple spheroids. We use the proposed technique to scan multicellular non-metastatic breast cancer cell spheroids embedded in gelatin methacryloyl (GelMA) hydrogels and co-register the micro-elastograms with fluorescence microscopy images.
Quantitative micro-elastography (QME) maps tissue elasticity. We report the first application of QME with encapsulation technique on skeletal muscles by demonstrating the variations of elasticity between normal and dystrophic mouse muscles.
Variations in the mechanical properties of the extracellular environment can alter important aspects of cell function such as proliferation, migration, differentiation and survival. However, many of the techniques available to study these effects lack the ability to characterise cell-to-cell and cell-to-environment interactions on the microscopic scale in three dimensions (3D). Quantitative micro-elastography (QME) is an extension of compression optical coherence elastography that utilizes a compliant layer with known mechanical properties to estimate the axial stress at the tissue surface, which combined with axial strain, is used to map the 3D microscale elasticity of tissue into an image. Despite being based on OCT, limitations in post-processing techniques used to determine axial strain prevented QME to quantify the elasticity of individual cells. In this study we extend the capability of QME to present, to the best of our knowledge, the first images of the elasticity of cells and their environment in 3D over millimeter field-of-views. We improve the accuracy and resolution of QME by incorporating an efficient, iterative solution to the inverse elasticity problem using adjoint elasticity equations to enable QME to visualize individual cells for the first time. We present images of human stem cells embedded in soft gelatin methacryloyl (GelMa) hydrogels and demonstrate these cells elevate the stiffness of the GelMa from 3-kPa to approximately 25-kPa. Our QME system is developed using commercially available components that can be readily made available to biologists, highlighting the potential for QME to emerge as an important tool in the field of mechanobiology.
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