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Adsorption, lubrication, and wear of lubricin on model surfaces : polymer brush-like behavior of a glycoprotein

journal contribution
posted on 2007-03-01, 00:00 authored by B Zappone, M Ruths, Wren Greene, G Jay, J Israelachvili
Using a surface force apparatus, we have measured the normal and friction forces between layers of the human glycoprotein lubricin, the major boundary lubricant in articular joints, adsorbed from buffered saline solution on various hydrophilic and hydrophobic surfaces: i), negatively charged mica, ii), positively charged poly-lysine and aminothiol, and iii), hydrophobic alkanethiol monolayers. On all these surfaces lubricin forms dense adsorbed layers of thickness 60–100 nm. The normal force between two surfaces is always repulsive and resembles the steric entropic force measured between layers of end-grafted polymer brushes. This is the microscopic mechanism behind the antiadhesive properties showed by lubricin in clinical tests. For pressures up to ∼6 atm, lubricin lubricates hydrophilic surfaces, in particular negatively charged mica (friction coefficient μ = 0.02–0.04), much better than hydrophobic surfaces (μ > 0.3). At higher pressures, the friction coefficient is higher (μ > 0.2) for all surfaces considered and the lubricin layers rearrange under shear. However, the glycoprotein still protects the underlying substrate from damage up to much higher pressures. These results support recent suggestions that boundary lubrication and wear protection in articular joints are due to the presence of a biological polyelectrolyte on the cartilage surfaces.

History

Journal

Biophysical journal

Volume

92

Issue

5

Pagination

1693 - 1708

Publisher

Cell Press

Location

St. Louis, Mo.

ISSN

0006-3495

eISSN

1542-0086

Language

eng

Publication classification

C1.1 Refereed article in a scholarly journal

Copyright notice

2007, by the Biophysical Society