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Force Microscopy of Non-adherent Cells: A Comparison of Leukemia Cell Deformability

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. Background.

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Force Microscopy of Non-adherent Cells: A Comparison of Leukemia Cell Deformability

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  1. 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

  2. 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

  3. 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

  4. Developing the Method • Used microfabricated wells to trap cells • Array of 8 – 20 µm diameter wells • Jurkat and HL60 cells trapped in 13.6 µm wells • Neutrophils trapped in 10.8 µm wells 50 µm 2 µm

  5. 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

  6. HL60s stiffer than Jurkat cells and neutrophils • consistent with a model of leukostasis • Stiffness contributes to vessel blockage 855 Pa 156 Pa 48 Pa

  7. 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

  8. Hertzian Model fits better • Gray line = data • Dash line = Hertzian mechanics model • Dotted line = Liquid droplet model

  9. 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

  10. Questions?

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