www.elsevier.com/locate/jmbbm Available online at www.sciencedirect.com Research Paper Microscale surface friction of articular cartilage in early osteoarthritis Jane Desrochers a , Matthias W. Amrein b , John R. Matyas c,n a McCaig Institute for Bone and Joint Health, University of Calgary, Calgary, AB, Canada T2N 4N1 b Director, Microscopy and Imaging Facility, Faculty of Medicine, University of Calgary, Calgary, AB, Canada T2N 4N1 c McCaig Institute for Bone and Joint Health, University of Calgary, Heritage Medical Research Building, HMRB 440, 3330 Hospital Drive NW, Calgary, AB, Canada T2N 4N1 article info Article history: Received 7 November 2012 Received in revised form 4 March 2013 Accepted 13 March 2013 Available online 2 April 2013 Keywords: Atomic force microscopy Articular cartilage surface Cartilage friction Osteoarthritis abstract Articular cartilage forms the articulating surface of long bones and facilitates energy dissipation upon loading as well as joint lubrication and wear resistance. In normal cartilage, boundary lubrication between thin films at the cartilage surface reduces friction in the absence of interstitial fluid pressurization and fluid film lubrication by synovial fluid. Inadequate boundary lubrication is associated with degenerative joint conditions such as osteoarthritis (OA), but relations between OA and surface friction, lubrication and wear in boundary lubrication are not well defined. The purpose of the present study was to measure microscale boundary mode friction of the articular cartilage surface in an in vivo experimental model to better understand changes in cartilage surface friction in early OA. Cartilage friction was measured on the articular surface by atomic force microscopy (AFM) under applied loads ranging from 0.5 to 5 μN. Microscale AFM friction analyses revealed depth dependent changes within the top-most few microns of the cartilage surface in this model of early OA. A significant increase of nearly 50% was observed in the mean engineering friction coefficient for OA cartilage at the 0.5 μN load level; no significant differences in friction coefficients were found under higher applied loads. Changes in cartilage surface morphology observed by scanning electron microscopy included cracking and roughening of the surface indicative of disruption and wear accompanied by an apparent disintegration of the thin surface lamina from the underlying matrix. Immunohistochemical staining of lubricin – an important cartilage surface boundary lubricant – did not reveal differences in spatial distribution near the cartilage surface in OA compared to controls. The increase in friction at the 0.5 μN force level is interpreted to reflect changes in the interfacial mechanics of the thin surface lamina of articular cartilage: increased friction implies reduced lubrication efficiency and a higher potential for cartilage surface wear in OA. The effects of mechanical or biochemical changes or loss of the thin surface lamina on the remaining tissue with respect to OA progression is unknown and requires further study, but preservation of the surface lamina seems an important early target for the maintenance of cartilage health and prevention of OA. & 2013 Elsevier Ltd. All rights reserved. 1751-6161/$ - see front matter & 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jmbbm.2013.03.019 n Corresponding author. Tel.: +1 403 220 7189. E-mail addresses: jedesroc@ucalgary.ca (J. Desrochers), mamrein@ucalgary.ca (M.W. Amrein), jmatyas@ucalgary.ca (J.R. Matyas). journal of the mechanical behavior of biomedical materials 25 (2013) 11–22