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Lecture: “MEMS based sensors for cellular studies” by Dr. Taher Saif.
Given August 10, 2006 during the GEM4 session at MIT in Cambridge, MA.
Please use the following citation format:
Saif, Taher. “MEMS based sensors for cellular studies.” Lecture,GEM4 session at MIT, Cambridge, MA, August 10, 2006.
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MEMS based sensors for cellular studies
Taher Saif
Mechanical Science and Engineering
University of Illinois at Urbana-Champaign
Part of GEM4 Summer School lectures on instruments for cell mechanics studies (Aug 10, 2006, MIT)
Objective
Develop portable micro sensors to study:
F
Anchorage
site
F
F
Actin filaments
• Cell mechanical response
F
• Cell adhesion
in different biochemical environments
to explore mechanotransduction and disease detection
U. of Illinois at Urbana-Champaign
Basic idea
A micro spring is used to measure cell force
Functionalized
probe
Cell membrane
U. of Illinois at Urbana-Champaign
Basic idea
Functionalized probe contacts a cell and forms
adhesion site
actin
Cell membrane
U. of Illinois at Urbana-Champaign
Basic idea
Probe is moved away from the cell. The cell applies
a force on the spring. The force is measured from the
spring deformation and its spring constant.
actin
Cell membrane
The cell may also be compressed or indented.
U. of Illinois at Urbana-Champaign
Cantilever as a mechanical spring
K (spring constant ) = 3EI/L3
L
P d
P = Kd
I=moment of inertia = width x depth3/12
Typical K ~ 10 nN/µm
Calibration: 1) Resonant frequency, geometry, elastic property
2) Comparing with another spring (e.g., AFM)
Simple implementation
Cell attached
to substrate
F=Kδ
Κ= 3EI /L3
δ
L
δ
F = cell force = Kδ
• Force sensor (such as a cantilever) is coated by fibronectin
• It is calibrated to determine spring constant, K
• The sensor tip is brought in contact with the cell - focal
adhesion sites form
• It is moved away from the cell. The cell force is measured from
the deformation δ
Advant ages: - Force sensor independent ly calibrat ed
- Force is applied at an anchorage sit e
- In-sit u observat ion
U. of Illinois at Urbana-Champaign
Experimental setup
1 µm
Resolut ion
o
Cell cult ure MEMS cant ilever 5
medium
SCS chip
z
Y
5o
cell
x
Y
Z
X-Y-Z
st age
X
Microscope
object ive
MEMS cant ilever
5o
2 0 nm resolut ion
piezo act uat or
Stage motion
5 deg
cell
U. of Illinois at Urbana-Champaign
MEMS force sensor: beams anchored at both ends
E
le
p
xam
Flexural springs (1µm wide)
Figure removed due to copyright restrictions.
Probe
K = 3.4 nN/µm
Yang and Saif.
Review of Scientific Instruments 76, 044301 (2005).
U. of Illinois at Urbana-Champaign
Courtesy Elsevier, Inc., http://www.sciencedirect.com. Used with permission.
E
le
p
x am
2D force sensor
Endothelial cells in a culture dish with MEMS cantilever
E
le
p
xam
Image removed due to copyright restrictions.
3-5 deg
5 deg
cell
Inverted
microscope
Schematic of the
MEMS cantilever
U. of Illinois at Urbana-Champaign
Force response of an endothelial cell
100
90
Cell deformation
80 begins
70
60
50
40
30
20
10
0
0
C1
4
2
A1
Microtubule
3
5
D1
B1
1
Cell deformation
20 O
40
60
80
100
120
Distance (µm) of the cantilever end from a fixed reference
C
Images removed due to copyright restrictions.
U. of Illinois at Urbana-Champaign
Force response of an endothelial cell
100
90
Cell deformation
80 begins
70
60
50
40
30
20
10
0
0
C1
4
2
A1
Microtubule
3
5
D1
B1
1
Just after
Cell deformation
20 O
40
60
80
100
120
Distance (µm) of the cantilever end from a fixed reference
C
Images removed due to copyright restrictions.
U. of Illinois at Urbana-Champaign
Force response of a monkey kidney fibroblast cell
120
Force (nN)
100
Cell force response under stretch is
linear and reversible
80
60
40
Forward
Backward
20
0
0
10
20
30
40
50
60
70
80
90
-20
Cell deformation (µm)
Reference: Yang and Saif. Experimental Cell Research 305 (2005) 42– 50.
U. of Illinois at Urbana-Champaign
Cyto-D treatment disrupts force bearing capacity
60
Stretching-1
Un-stretching-1
50
Stretching-2
Un-stretching-2
Strecthing-3
Un-strecthing-3
40
Before
CytoD
30
Cyto-D disrupts
actin network
Monkey kidney fibroblast
20
After
CytoD
10
0
-10
0
5
10
15
20
25
Cell stretching (µm)
30
35
40
Reference: Yang and Saif. Experimental Cell Research 305 (2005) 42– 50.
U. of Illi ois at Urbana-Champaign
Force response of a monkey kidney fibroblast cell
Force (nN)
Cell response under indentation is30
non-linear and hysteretic
25
Tension
20
(3)
15
Push-1
Pull-1
Push-2
Pull-2
10
5
(4)
-45
-40
-35
-30
-25
-20
0
-15
-10
-5
0
5
10
15
20
25
30
-5
(2)
Indentation
(1)
-10
-15
Cell deformation (µm)
U. of Illinois at Urbana-Champaign
Mechanism of non-linearity and irreversibility under indentation
GFP actin
Image removed due to copyright restrictions. Photograph of GFP actin protein.
140
120
100
80
60
40
20
0
-20 0
5
10
15
20
Indentation
25
30
35
40
Actin agglomerates irreversibly under indentation
Images removed due to copyright restrictions.��
Images of GFP actin undergoing indentation.
Yang and Saif Actabiomaterialia 2006 (in press) More evidence of actin agglomeration
Images removed due to copyright restrictions.
Actin in monkey kidney fibroblast is subjected to indentation.
probe
45 µm
38:42
48:00
44:18
71:42
Monkey kidney fibroblast subjected to mechanical indentation (injury simulation). Here actin stress fibers
are highlighted by green florescent protein (GFP). In response to indentation, the cell signals local
actin agglomeration at discrete locations. Such actin agglomeration is also observed in various physiological
conditions such as during ischemic attack in kidney cells. This is the first evidence of actin agglomeration due
to mechanical stimulus (Shengyuan and Saif, Actabiomaterialia 2006, in press).
Actin agglomeration in physiological condition: ischemic attack
Image removed due to copyright restrictions.
Figure 5c in Ashworth, Sharon L., et al. "ADF/cofilin Mediates Actin Cytoskeletal Alterations in LLC-PK Cells During ATP Depletion." American Journal of Physiology - Renal Physiology 284 (2003): F852-F862.
Porcine kidney cells
Ashworth et al. Am J. Physiol Renal Physiol 284: F852, 2003.
Why MEMS bio sensors:
1. Force range: 1-100 nN (natural progression
from optical tweezer, magnetic beads, AFM) 1. Flexibility of design (cell contact region may
be designed in a variety of fashions)
3. Large cell deformation range (sub µm-10s of µm)