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Published byLaureen Nelson Modified over 9 years ago
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Force Microscopy of Non-adherent Cells: A Comparison of Leukemia Cell Deformability Michael J. Rosenbluth, Wilbur A. Lam, and Daniel A. Fletcher Biophysical Journal, 2006 Sophie Wong 20.309, MIT November 20, 2008
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Background AFM used to quantify mechanical properties of biological material Current methods for measuring elasticity and viscoelasticity – Require indentation of cells adhered to substrate – Not feasible for non-adherent cells Increased stiffness of lymphocytes may be the cause of diabetes mellitus and leukemia
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Three Goals Develop method for characterizing and comparing deformability of leukemia cells Compare mechanical properties of – myeloid (HL60) and lymphoid (Jurkat) lines – normal neutrophils Compare Hertzian Mechanics Model vs. Liquid Droplet Model
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Developing the Method Used microfabricated wells to trap cells 50 µm2 µm Array of 8 – 20 µm diameter wells Jurkat and HL60 cells trapped in 13.6 µm wells Neutrophils trapped in 10.8 µm wells
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Deflection-position curve Cantilever deflection small compared to indentation Piezo platform extended at constant rate = 1506 nm/s Deflect cantilever until ~ 800pN applied or cell indented 3 µm HL60
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HL60s stiffer than Jurkat cells and neutrophils consistent with a model of leukostasis Stiffness contributes to vessel blockage 855 Pa 48 Pa 156 Pa
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Fitting the model Models used to determine cell elasticity and viscoelasticity Hertzian Mechanics Model assumptions – Homogeneous, Isotropic, Linear, Elastic (HILE) – Material undergoes infinitesimally small strains Liquid Droplet Model assumptions – Internal contents are homogeneous viscous – Cortical tension constant around cell – Cortical shell deforms around tip during indentation – Radius of cell remains constant during indentation
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Hertzian Model fits better Gray line = data Dash line = Hertzian mechanics model Dotted line = Liquid droplet model
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Significance & Future Studies Deformability of leukemic cells plays important role in leukostasis Where does difference in cell stiffness originate? – Filament networks? – Cytoplasm? – Nuclear or cell membranes? Investigate other factors involved in leukostasis: adhesion, transmigration
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Questions?
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