title: Cartilage aggrecan can undergo self-adhesion.
abstract: Here it is reported that aggrecan, the highly negatively charged macromolecule in the cartilage extracellular matrix, undergoes Ca(2+)-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 approximately 2.5 mum) at a density ( approximately 40 mg/mL) that simulates physiological conditions in the tissue ( approximately 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 + CaCl(2) ([Cl(-)] = 0.15 M, [Ca(2+)] = 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 Ca(2+) 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.
authors.affiliation: Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA.
authors.forename: Lin
authors.initials: L
authors.lastname: Han
authors.forename: Delphine
authors.initials: D
authors.lastname: Dean
authors.forename: Laura A
authors.initials: LA
authors.lastname: Daher
authors.forename: Alan J
authors.initials: AJ
authors.lastname: Grodzinsky
authors.forename: Christine
authors.initials: C
authors.lastname: Ortiz
mesh_terms: D000268:Adhesiveness; D053674:Aggrecans / Q000737:chemistry*; D000818:Animals; D001665:Binding Sites; D002358:Cartilage, Articular / Q000737:chemistry*; D002417:Cattle; D003198:Computer Simulation; D008956:Models, Chemical; D046912:Multiprotein Complexes / Q000737:chemistry; D011485:Protein Binding; D013314:Stress, Mechanical
chemical_list: D053674:Aggrecans; D046912:Multiprotein Complexes