title: Interaction of lubricin with type II collagen surfaces: adsorption, friction, and normal forces.
abstract: One of the major constituents of the synovial fluid that is thought to be responsible for chondroprotection and boundary lubrication is the glycoprotein lubricin (PRG4); however, the molecular mechanisms by which lubricin carries out its critical functions still remain largely unknown. We hypothesized that the interaction of lubricin with type II collagen, the main component of the cartilage extracellular matrix, results in enhanced tribological and wear properties. In this study, we examined: (i) the molecular details by which lubricin interacts with type II collagen and how binding is related to boundary lubrication and adhesive interactions; and (ii) whether collagen structure can affect lubricin adsorption and its chondroprotective properties. We found that lubricin adsorbs strongly onto denatured, amorphous, and fibrillar collagen surfaces. Furthermore, we found large repulsive interactions between the collagen surfaces in presence of lubricin, which increased with increasing lubricin concentration. Lubricin attenuated the large friction and also the long-range adhesion between fibrillar collagen surfaces. Interestingly, lubricin adsorbed onto and mediated the frictional response between the denatured and native amorphous collagen surfaces equally and showed no preference on the supramolecular architecture of collagen. However, the coefficient of friction was lowest on fibrillar collagen in the presence of lubricin. We speculate that an important role of lubricin in mediating interactions at the cartilage surface is to attach to the cartilage surface and provide a protective coating that maintains the contacting surfaces in a sterically repulsive state.
authors.affiliation: Department of Mechanical Engineering and Materials Science, Duke University, Durham, NC 27708, USA; Center for Biologically Inspired Materials and Material Systems, Duke University, Durham, NC 27708, USA.
authors.forename: Debby P
authors.initials: DP
authors.lastname: Chang
authors.affiliation: Department of Mechanical Engineering and Materials Science, Duke University, Durham, NC 27708, USA; Center for Biomolecular and Tissue Engineering, Duke University, Durham, NC 27708, USA; Department of Orthopaedic Surgery, Duke University, Durham, NC 27710, USA.
authors.forename: Farshid
authors.initials: F
authors.lastname: Guilak
authors.affiliation: Department of Emergency Medicine, and Brown University, Providence, RI 02903, USA.
authors.forename: Gregory D
authors.initials: GD
authors.lastname: Jay
authors.affiliation: Department of Mechanical Engineering and Materials Science, Duke University, Durham, NC 27708, USA; Center for Biologically Inspired Materials and Material Systems, Duke University, Durham, NC 27708, USA; Center for Biomolecular and Tissue Engineering, Duke University, Durham, NC 27708, USA. Electronic address: zauscher@duke.edu.
authors.forename: Stefan
authors.initials: S
authors.lastname: Zauscher
mesh_terms: D000327:Adsorption; D000818:Animals; D002358:Cartilage, Articular / Q000378:metabolism*; D002645:Chickens; D024043:Collagen Type II / Q000737:chemistry* / Q000493:pharmacokinetics*; D003102:Colloids / Q000378:metabolism; D017276:Friction; D006023:Glycoproteins / Q000737:chemistry* / Q000493:pharmacokinetics*; D006801:Humans; D008153:Lubrication; D018625:Microscopy, Atomic Force; D011485:Protein Binding / Q000502:physiology; D011489:Protein Denaturation; D017433:Protein Structure, Secondary; D013499:Surface Properties; D013582:Synovial Fluid / Q000378:metabolism; D000099158:Proteoglycan 4
chemical_list: D024043:Collagen Type II; D003102:Colloids; D006023:Glycoproteins; D000099158:Proteoglycan 4
keywords: Atomic force microscope; Boundary lubrication; Collagen; Colloidal probe microscopy; Friction; Glycoproteins; Lateral force microscopy; Lubricin; PRG4; SAMs; Tribology; Type II collagen; Wear