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 13-4022 Phone : (617) 452-3084 Email : cortiz@mit.edu WWW : http://web.mit.edu/cortiz/www

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

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

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

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

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

Knee Structure Ernzt Hunziker

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

Structure of Aggrecan HA (Rotary Shadowing EM : Hardingham, et al. FASEB J. 1992. Mörgelin, et al. Biophys. Chem. 1994.) HA - b n=25.5

● 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.

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

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

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

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

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 0.0001M B 0.001M C 0.01M D 0.1M E 1M A electrostatic double layer B C D E