Journal
BIOPHYSICAL JOURNAL
Volume 95, Issue 10, Pages 4862-4870Publisher
BIOPHYSICAL SOC
DOI: 10.1529/biophysj.107.128389
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Funding
- National Science Foundation [0403903]
- National Institutes of Health [AR45779]
- Whitaker Foundation Fellowshi
- Div Of Civil, Mechanical, & Manufact Inn
- Directorate For Engineering [0758651] Funding Source: National Science Foundation
- Div Of Engineering Education and Centers
- Directorate For Engineering [0403903] Funding Source: National Science Foundation
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Here it is reported that aggrecan, the highly negatively charged macromolecule in the cartilage extracellular matrix, undergoes Ca2+-mediated self-adhesion after static compression even in the presence of strong electrostatic repulsion in physiological-like solution conditions. Aggrecan was chemically end-attached onto gold-coated planar silicon substrates and gold-coated microspherical atomic force microscope probe tips (end radius R approximate to 2.5 mu m) at a density (similar to 40 mg/mL) that simulates physiological conditions in the tissue (similar to 20-80 mg/mL). Colloidal force spectroscopy was employed to measure the adhesion between opposing aggrecan monolayers in NaCl (0.001-1.0 M) and NaCl + CaCl2 ([Cl-] = 0.15 M, [Ca2+] = 0-75 mM) aqueous electrolyte solutions. Aggrecan self-adhesion was found to increase with increasing surface equilibration time upon compression (0-30 s). Hydrogen bonding and physical entanglements between the chondroitin sulfate-glycosaminoglycan side chains are proposed as important factors contributing to aggrecan self-adhesion. Self-adhesion was found to significantly increase with decreasing bath ionic strength ( and hence, electrostatic double-layer repulsion), as well as increasing Ca2+ concentration due to the additional ion-bridging effects. It is hypothesized that aggrecan self-adhesion, and the macromolecular energy dissipation that results from this self-adhesion, could be important factors contributing to the self-assembled architecture and integrity of the cartilage extracellular matrix in vivo.
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