1. Materials and Biomaterials MOLECULAR MECHANICS OF CARTILAGE
3.052 Nanomechanics of
Materials and Biomaterials
LECTURE # 14 : • ELECTROSTATIC FORCES BETWEEN CHARGED SURFACES IN LIQUIDS &
MOLECULAR MECHANICS OF CARTILAGE
Prof. Christine Ortiz
DMSE, RM
Phone : (617)
WWW :

2. Interaction Between Two Similarly Charged Surfaces
In the Presence of an Electrolyte
D2 <D1 D1 s s rs e rs rs
(rx+) rs ro
r =ro
counterions(rx+) x
x=-D/2
coions(rx-)
x=0
x=+D/2
x=-D/2
x=0
x=+D/2

3. Electric Potential of a Charged Surfaces
In the Presence of an Electrolyte s
yo=ys yx
yo/e c3 c2 c1
x=0 x
1/k1
1/k2
1/k3

4. Interaction Between Two Similarly Charged Surfaces
In the Presence of an Electrolyte
D2 <D1 x
x=0
x=-D/2
x=+D/2 yx
yo=ys ym
D2 <D1 x
x=0
x=-D/2
x=+D/2 yx
yo=ys ym
increased
electrolyte
concentration

5. (*Derjaguin-Landau-Verwey-Overbeek)
The DLVO* Theory
(*Derjaguin-Landau-Verwey-Overbeek)

6. (*Derjaguin-Landau-Verwey-Overbeek)
The DLVO* Theory
(*Derjaguin-Landau-Verwey-Overbeek)
Double Layer Repulsion
Total
van der Waals attraction

7. Knee Structure
Ernzt Hunziker

8. Structural Hierarchy and Function of
the Components of Articular Cartilage
(*Buckwalter, et al., J. Bio. Chem.,1982)
H2O~65-80% vol.

9. Structure of Aggrecan HA
(Rotary Shadowing EM : Hardingham, et al. FASEB J Mörgelin, et al. Biophys. Chem ) HA - b
n=25.5

10. ● individual aggrecan monomers and GAG chains are clearly visualized
TMAFM Images of Sparse Monolayer of Fetal Bovine Articular Cartilage Aggrecan Monomers (A1A1D1D1) in Air on APS-Mica
(Ng, et al. Polym. Prepr. 2003)
amplitude
height
● 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.

11. TMAFM Images of Sparse Monolayer of Cartilage Aggrecan Monomers (A1A1D1D1) in Air on APS-Mica
(Ng, et al. Polym. Prepr. 2003)
1.1 nm
50 nm
50 nm
0.6 nm
FETAL
MATURE
0 nm

12. 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
● h< 8.4±2.3Å (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

13. (Seog, et al. Macromolecules 2002)
Nanomechanics.....
(Seog, et al. Macromolecules 2002)
~32 nm

14. FTOTAL = F D FELECTROSTATIC + FSTERIC + FVDW + FHYDRATION
microfabricated cantilever
(Seog, et al. Macromolecules 2002)
Chemical HRFS :
Sulfate-Functionalized
Probe Tip versus GAG
Brush Surface -
Rtip~25 nm - - - + - - + - - + - - - - + - - - - + + - - - - + + - - - - - - - + + + - + + + +
s1(-) + + + - + - + + +
tip diffuse
counterion
double layer - + + - + + + +
Si3N4 probe tip : Au-coated + + + + + + + + + + + + + + + - + + - + - + + + + + + D + - + - +
bulk
concentration
of electrolyte ions + - - + - + - - - + - + + + - +
FTOTAL =
FELECTROSTATIC
+ FSTERIC
+ FVDW
+ FHYDRATION + - + - + + + +
surface diffuse
counterion double layer + + + - + + + + + - + - + + + + + + + + + + + + + + + + - - - - + - - - + + - + - - + - - + + + - + - - - - + - - + - - - - - + - - - - -
end-grafted CS-GAG brush on a planar surface + - - - - +
s2(-) + - - + - + - - - + + - + + + - + - + - + - - + + + - - - - + - - + - + - - - - - - + - + - + - - + - + - - - + + - - + - - + + - + - - - + + - + - - - + - + - - - - - - Si + + + - + - +
CH3 SAM
Au-coated silicon chip
s~6.5 nm

15. SULFATE-Functionalized Probe Tip versus GAG Surface
at pH=5.6 as a Function of NaCl Ionic Strength
AVERAGED CURVES ON APPROACH
(Seog, et al. Macromolecules 2002)
Lcontour(GAG)
steric
+VDW+lateral
intermolecular
electrostatic+hydration
A M
B 0.001M
C 0.01M
D 0.1M
E 1M A
electrostatic
double layer B C D E