Tunable Lubricin-mimetics for Boundary Lubrication of Cartilage

Abstract

The glycoprotein lubricin is the primary boundary lubricant of articular cartilage. Its boundary lubricating abilities arise from two key structural features: i) a dense mucin-like domain consisting of hydrophilic oligosaccharides and ii) an end terminus that anchors the molecule to articulating surfaces. When bound, lubricin molecules attract and trap water near a surface, reducing friction and facilitating glide. Synthetic analogues were previously created to mimic lubricin using thiol-terminated polyacrylic acid-graft-polyethylene glycol (pAA-g-PEG) brush copolymers. The PEG moiety was designed to mimic the mucin-like domain of lubricin and the thiol-terminus was designed to anchor the molecules to cartilage surfaces, mimicking the binding domain. In this study, these synthetic lubricin-mimetics were bound to gold-coated surfaces to characterize the relationship between the polymers' molecular architecture and their lubricating capacity. A library of nine copolymer brushes was synthesized using different sizes of pAA and PEG. Larger molecular weight polymers created smoother, more densely covered surfaces (p<0.05). Additionally, the hydrodynamic sizes of the polymers in solution were correlated with their lubricating abilities (p<0.05). Friction coefficients of cartilage against polymer-treated gold surfaces were lower than cartilage against untreated surfaces (Δμeq=−0.065±0.050 to −0.093±0.045, p<0.05).