1. Magnetic Tweezer System Development
Probing mechanical properties across multiple scales
Jason Sherfey
Senior BME, Vanderbilt University
Advisor: Dr. Franz Baudenbacher

2. Force displacement measurements on magnetic beads linked to the cell surface through E-Cadherin
1 nN 1 2 3
displacement [mm]
Time [s] F
T=0 s
T=1.5 s
Fit to Mechanical Analog
Extract Model parameter

3. Force-Displacement Curves MDCK cells
Wild-type
P120 Knockout

4. Viscosity (Pa-s-m)
N = 10

5. Elasticity (Pa-m)
N = 10

6. Relaxation Time (s)
N = 10

7. Viscosity (Pa-s-m) Elasticity (Pa-m) Relaxation Time (s) p = 0.364
0.0020
0.0044
Wild-type MDCK
0.0019
0.0038
P120 Knockout MDCK
Standard Deviation
Mean
p = 0.364
No significant difference in WT & KO Viscosities
Elasticity (Pa-m)
0.0088
0.0217
Wild-type MDCK
0.0106
0.0118
P120 Knockout MDCK
Standard Deviation
Mean
p =
WT Elasticity is significantly larger than KO
Relaxation Time (s)
0.0006
0.0421
Wild-type MDCK
0.0725
P120 Knockout MDCK
Standard Deviation
Mean
p =
WT Relaxation Time is significantly faster than KO
N = 10 cells

8. Conclusions
The stiffness and relaxation time constants are significantly different in p120 knockout and wild-type MDCK cells.
2. The stiffness decreases & relaxation time slows down when p120 expression is reduced in MDCK cells.

9. Strain Hardening
Stiffness (Pa-m)
The stiffness of the adhesion protein linker system increases when stress is repeatedly applied.
Pull 
Wild-type Cell 1
0.0132 2
0.0152 3
0.0193 4
0.0249
Knockout Cell
0.0051
0.0063
0.0081