MEMS based sensors for cellular studies - Amazon S3
Transcript of MEMS based sensors for cellular studies - Amazon S3
MEMS based sensors for cellular studies
Taher SaifMechanical 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)
Anchoragesite
Actin filaments
Develop portable micro sensors to study:
• Cell mechanical response
• Cell adhesion
in different biochemical environmentsto explore mechanotransduction and disease detection
U. of Illinois at Urbana-Champaign
Objective
F
FF
F
Cell membrane
Basic idea
U. of Illinois at Urbana-Champaign
Functionalized probe
A micro spring is used to measure cell force
actin
Cell membrane
U. of Illinois at Urbana-Champaign
Basic idea
Functionalized probe contacts a cell and formsadhesion site
actin
Cell membrane
U. of Illinois at Urbana-Champaign
Basic idea
Probe is moved away from the cell. The cell appliesa force on the spring. The force is measured from the spring deformation and its spring constant.
The cell may also be compressed or indented.
P dK (spring constant ) = 3EI/L3
P = Kd
Typical K ~ 10 nN/µm
Calibration: 1) Resonant frequency, geometry, elastic property2) Comparing with another spring (e.g., AFM)
Cantilever as a mechanical spring
L
I=moment of inertia = width x depth3/12
Simple implementation
U. of Illinois at Urbana-Champaign
Lδ
Κ= 3EI /L3F=Kδ
δ
Cell attachedto substrate
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 - focaladhesion sites form
• It is moved away from the cell. The cell force is measured fromthe deformation δ
Advantages: - Force sensor independent ly calibrated- Force is applied at an anchorage site- In-situ observat ion
U. of Illinois at Urbana-Champaign
Experimental setup 1 µmResolut ion
20nm resolut ionpiezo actuator
xY
z
cell
MEMS cant ileverCell culturemedium SCS chip
Microscope object ive
5o
5oX-Y-Zst age
X
ZY
cell
5 deg5o
Stage motionMEMS cant ilever
U. of Illinois at Urbana-Champaign
MEMS force sensor: beams anchored at both ends
F = Kx
xSisubstrate
K = 3.4 nN/µm
Cell
Probe
Probe
Flexural springs (1µm wide)
Yang and Saif. Review of Scientific Instruments 76, 044301 (2005).
Example
2D force sensorExample
U. of Illinois at Urbana-Champaign
Endothelial cells in a culture dish with MEMS cantilever
Bovine endothelialcells on a substrate
MEMS cantilevercoated with fibronectin (K=18nN/µm)
100µm
The MEMS cantilever has formed adhesivecontact with the cell
5 deg3-5 deg
Schematic of theMEMS cantilever
Invertedmicroscope
cell
Example
U. of Illinois at Urbana-Champaign
Force response of an endothelial cell
Microtubule
C0
102030405060708090
100
0 20 40 60 80 100Distance (µm) of the cantilever end from a fixed reference
B1D1
C1
120
1
2 34
5
OCell deformation
Cell deformationbegins
A1
Necking
Motion
A1 B1Endothelialcell
C1
D
D1
Just afterfailure
Relaxedcell
g
U. of Illinois at Urbana-Champaign
Force response of an endothelial cell
Microtubule
C0
102030405060708090
100
0 20 40 60 80 100Distance (µm) of the cantilever end from a fixed reference
B1D1
C1
120
1
2 34
5
OCell deformation
Cell deformationbegins
A1
Necking
Motion
A1 B1Endothelialcell
C1
D
D1
Just afterfailure
Relaxedcell
g
U. of Illinois at Urbana-Champaign
Force response of a monkey kidney fibroblast cell
-20
0
20
40
60
80
100
120
0 10 20 30 40 50 60 70 80 90
Cell deformation (µm)
ForwardBackward
Forc
e (n
N)
Yang and Saif. Experimental Cell Research 305 (2005) 42– 50.
Cell force response under stretch is linear and reversible
-10
0
10
20
30
40
50
60
0 5 10 15 20 25 30 35 40Cell stretching (µm)
Stretching-1Un-stretching-1Stretching-2Un-stretching-2Strecthing-3Un-strecthing-3Before
CytoD
After CytoD
Monkey kidney fibroblast
U. of Illi ois at Urbana-Champaign
Cyto-D treatment disrupts force bearing capacity
Yang and Saif. Experimental Cell Research 305 (2005) 42– 50.
Cyto-D disruptsactin network
U. of Illinois at Urbana-Champaign
Force response of a monkey kidney fibroblast cell
-15
-10
-5
0
5
10
15
20
25
30
-45 -40 -35 -30 -25 -20 -15 -10 -5 0 5 10 15 20 25 30
Cell deformation (µm)
Push-1Pull-1Push-2Pull-2
(1)(2)
(3)
(4)Fo
rce
(nN
)
Tension
Indentation
Cell response under indentation is non-linear and hysteretic
-20
0
20
40
60
80
100
120
140
0 5 10 25 30 35 40
Indentation
15 20
Mechanism of non-linearity and irreversibility under indentation
GFP actin
Force measured from change of gap betweentwo markers
Sl=2.8, R ~ tα, α=2.8
α=.7
Log(
dia)
Log(time)
Actin agglomerates irreversibly under indentation
Yang and SaifActabiomaterialia 2006 (in press)
44:1848:00 71:42
Monkey kidney fibroblast subjected to mechanical indentation (injury simulation). Here actin stress fibersare highlighted by green florescent protein (GFP). In response to indentation, the cell signals localactin agglomeration at discrete locations. Such actin agglomeration is also observed in various physiologicalconditions such as during ischemic attack in kidney cells. This is the first evidence of actin agglomeration dueto mechanical stimulus (Shengyuan and Saif, Actabiomaterialia 2006, in press).
38:42
45 µm
probe
More evidence of actin agglomeration
Actin agglomeration in physiological condition: ischemic attack
Ashworth et al. Am J. Physiol Renal Physiol 284: F852, 2003.
Porcine kidney cells
Why MEMS bio sensors:
1. Force range: 1-100 nN (natural progressionfrom 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)