Force Microscopy of Nonadherent Cells: A

Comparison of Leukemia Cell Deformability

Rosenbluth, Lam, and Fletcher (2006)

Presented by: Aisha Bobb-Semple20.309

November 20, 2008

Background Leukemia causes decreased deformability

and increased adhesion in myeloblasts and lymphoblasts.

This can lead to leukostasis – cell aggregation in vasculature.

Leukostasis can cause intracranial hemorrhages, respiratory failure, and ultimately death.

More knowledge about deformability is necessary for a better understanding of the disease.

Examples of Leukostasis

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Goals Develop a technique for probing non-

adherent cells. Develop a model for characterization

mechanical properties. Compare the deformability of: Acute

myeloid leukemia (AML) and acute lymphoid leukemia (ALL) cell lines, and human neutrophils

Use of AFM for measuring stiffness

Cells are usually firmly adhered to a substrate

Cell is indented by a cantilever at a constant rate

Deflection of the cantilever is measured and related to force.

Linear elastic model of cell based on Hertzian mechanics is commonly used to determine elasticity.

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Use of AFM for measuring stiffness Leukocytes are non-

adhesive. One solution is to coat

the surface of the substrate with polypeptides

Microfabricated wells were developed to immobilize the cells

Model for Characterization

Which of two models best describes deformability of the cells?

At what deformation rates are viscous contributions from the cytoplasm of the

cell minimized?

Model ComparisonHertzian Mechanics Model

Indentation is related to the load Piezo position related to cantilever

deflection

Liquid Droplet Model Used predominantly in micropipette

experiments Difference in pressure related to cortical

tension which is then related to deflection of the cantilever

Model Comparison Both models were fit

to experimental data Mean squared error

for the Hertz model was lower than the liquid drop model

Hertzian model used for cell stiffness comparison

Optimal Deformation Rate?

Stiffness remained constant at and below 415nm/s for AML cells. (948 nm/s for ALL cells and 501nm/s for neurtrophils)

Comparison of Deformability

AML cells found to be significantly stiffer than others.

This is not surprising since leukostasis occurs in much higher frequency in AML.

Common for clinicians to accept that AML cells are more rigid than ALL and neutrophils.

Summary Developed microwells to immobilize non-adherent

cells for atomic force microscopy. Determined that the Hertz model best fits the

data. Determined that AML cells were significantly

stiffer than ALL cells and neutrophils Consistent with finding that myeloid leukemias

result in leukostasis more frequently than lymphoid leukemias do.

QUESTIONS??

~Thank you for your attention~