3.052 Nanomechanics of

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3.052 Nanomechanics of Materials and
Biomaterials
LECTURE 14 ELECTROSTATIC FORCES
BETWEENCHARGED SURFACES IN LIQUIDS MOLECULAR
MECHANICS OF CARTILAGE
Prof. Christine Ortiz DMSE, RM 13-4022 Phone
[phone] Email cortiz_at_mit.edu WWW
http//web.mit.edu/cortiz/www
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Interaction Between Two Similarly Charged
Surfaces In the Presence of an Electrolyte
D2 ltD1
D1
s
s
rs
rs
e
rs
(rx)
rs
ro
r? ro
counterions(rx)
x
coions(rx-)
x0
x-D/2
xD/2
x-D/2
xD/2
x0
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Electric Potential of a Charged Surfaces In the
Presence of an Electrolyte
s
yoys
yx
c3
yo/e
c2
c1
x
x0
1/k1
1/k2
1/k3
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Interaction Between Two Similarly Charged
Surfaces In the Presence of an Electrolyte
increased electrolyte concentration
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The DLVO Theory (Derjaguin-Landau-Verwey-Overbe
ek)
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The DLVO Theory (Derjaguin-Landau-Verwey-Overbe
ek)
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Knee Structure
Ernzt Hunziker
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Structural Hierarchy and Function of the
Components of Articular Cartilage
(Buckwalter, et al., J. Bio. Chem.,1982)
H2O65-80 vol.
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Structure of Aggrecan (Rotary Shadowing EM
Hardingham, et al. FASEB J. 1992. Mörgelin, et
al. Biophys. Chem. 1994.)
HA
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TMAFM Images of Sparse Monolayer of Fetal Bovine
Articular Cartilage Aggrecan Monomers (A1A1D1D1)
in Air on APS-Mica (Ng, et al. Polym. Prepr. 2003)
height
amplitude
? individual aggrecan monomers and GAG chains are
clearly visualized ? a thin layer of H2O keeps
the aggrecan partially hydrated (Sheiko et al.
Adv. Poly. Sci. 2000) giving an environment
closer to physiological conditions than complete
drying.
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TMAFM Images of Sparse Monolayer of Cartilage
Aggrecan Monomers (A1A1D1D1) in Air on
APS-Mica (Ng, et al. Polym. Prepr. 2003)
1.1 nm
0.6 nm
FETAL
MATURE
0 nm
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TMAFM Amplitude Images of Dense Monolayer of
Fetal Bovine Articular Cartilage Aggrecan
Monomers (A1A1D1D1) in Air on APS-Mica (Ng, et
al. Polym. Prepr. 2003)
? Core protein backbone has some degree of
flexibility and conform to each other ? hlt
8.42.3Å (diameter of 1 GAG chain 6Å) measured
heights are much smaller than expected, which are
attributed to compression by the probe tip and
attractive interactions with the surface
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Nanomechanics..... (Seog, et al. Macromolecules
2002)
32 nm
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microfabricated cantilever
F
(Seog, et al. Macromolecules 2002)
Chemical HRFS Sulfate-Functionalized Probe Tip
versus GAG Brush Surface
Rtip25 nm
s1(-)
tip diffuse counterion double layer
Si3N4 probe tip Au-coated

bulk concentration of electrolyte ions
D
FTOTAL FELECTROSTATIC FSTERIC FVDW
FHYDRATION
surface diffuse counterion double layer
end-grafted CS-GAG brush on a planar surface
s2(-)
CH3 SAM Au-coated silicon chip
Si
s6.5 nm
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SULFATE-Functionalized Probe Tip versus GAG
Surface at pH5.6 as a Function of NaCl Ionic
Strength
AVERAGED CURVES ON APPROACH
(Seog, et al. Macromolecules 2002)
Lcontour(GAG)
steric VDWlateral intermolecular electrostatic
hydration
A 0.0001M B 0.001M C 0.01M D 0.1M E 1M
A
electrostatic double layer
B
C
D
E