23.2 Cartilage lubrication and diarthroidal joint MechanoBiology (original) (raw)
Related papers
The Role of the Surface Amorphous Layer of Articular Cartilage in Joint Lubrication
Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine, 2006
Articular cartilage is a complex soft tissue that performs multiple functions in the joint. In particular, the amorphous layer that covers the surface of articular cartilage is thought to play some role in lubrication. This study aimed to characterize the surface amorphous layer (SAL) using a variety of techniques, including environmental scanning electron microscopy, transmission electron microscopy, white light interferometry, and biochemical analysis of its composition. Friction tests were conducted to investigate the role of the SAL in lubrication. A protocol to remove successfully the SAL without damaging the underlying cartilage was developed and the material removed from healthy cartilage was found to contain approximately equal quantities of glycosaminoglycan (GAG), protein, and lipid. Cartilage-on-cartilage friction tests were conducted on fresh, healthy cartilage with and without the SAL, under both dynamic and static operating conditions. Removal of the SAL was not found to change the friction coefficient. However, subsequent staining of specimens indicated that the SAL had replenished during the test following loading. The replenished SAL was characterized and found to contain lipids and sulphated GAGs with undetectable protein. This study revealed experimental evidence of surface layer replenishment in articular cartilage. It was postulated that the surface layer regeneration mechanism was purely mechanical and associated with movement of GAGs and lipids through the cartilage matrix during deformation, since the experimental set-up did not contain any means of biochemical activation. mixed or boundary lubrication where some surface Engineering, University of Leeds, Leeds, LS2 9JT, UK. email: contact can occur [10-13]. It has been postulated that an increase in loading time results in a reduction s.graindorge@leeds.ac.uk JEIM122
Biotribology, 2017
Quantifying surface damage on articular cartilage after exposure of the tissue to extreme or prolonged mechanical stress is not only relevant for evaluating clinically relevant alterations, e.g. when the physiological lubrication mechanisms fail, but also useful for assessing the suitability of artificial cartilage replacement materials, implants or synovia-mimetic lubricants. Here, we establish a systematic quantification method for cartilage wear formation which is based on optical profilometrya variant of confocal microscopy. With this approach, we compare three different macromolecular lubricants, i.e. solutions containing either hyaluronic acid, lubricin or porcine gastric mucin. Depending on the counter material used for tribological testing and the macromolecule used for lubrication, we detect different types of tissue damage which we quantify with suitable topographical parameters. In our setup, mucin solutions outperform the other two lubricants: when using mucin solutions for lubrication, we do not find any signs of topographical alterations on the cartilage surface. Our results underscore the supreme protective abilities of mucin solutions-even on biological surfaces where they do not occur physiologically.
Atomic force microscope investigation of the boundary-lubricant layer in articular cartilage
Osteoarthritis and Cartilage, 2010
Objective: To determine the roles of superficial zone protein (SZP), hyaluronan (HA), and surface-active phospholipids (SAPL) in boundary lubrication of articular cartilage through systematic enzyme digestion using trypsin, hyaluronidase, and phospolipase-C (PLC) surface treatments. Methods: The friction coefficient of articular cartilage surfaces was measured with an atomic force microscope (AFM) before and after enzyme digestion. Surface roughness, adhesion, and stiffness of the articular surface were also measured to determine the mechanism of friction in the boundary lubrication regime. Histology and transmission electron microscopy were used to visualize the surface changes of treatment groups that showed significant friction changes after enzyme digestion. Results: A significant increase in the friction coefficient of both load-bearing and non load-bearing regions of the joint was observed after proteolysis by trypsin. Treatment with trypsin, hyaluronidase, or PLC did not affect the surface roughness. However, trypsin treatment decreased the adhesion significantly. Results indicate that the protein component at the articular cartilage surface is the main boundary lubricant, with SZP being a primary candidate. The prevailing nanoscale deformation processes are likely plastic and/or viscoelastic in nature, suggesting that plowing is the dominant friction mechanism. Conclusions: The findings of this study indicate that SZP plays an intrinsic and critical role in boundary lubrication at the articular surface of cartilage, whereas the effects of HA and SAPL on the tribological behavior are marginal.
Osteoarthritis and cartilage / OARS, Osteoarthritis Research Society, 2009
Earlier in vitro studies have shown that the coefficient of friction (COF) of cartilage decreases with increasing load at the lower end of the physiological loading spectrum. At these lower load levels, depletion of glycosaminoglycans (GAGs) from native cartilage has been shown to elevate the COF levels. The current study evaluated the long-term friction, deformation and wear of native and GAG deficient cartilage at a wide range of physiological stress levels in vitro. A pin-on-plate machine (sliding velocity: 4 mm/s and stroke length: 4 mm) was used to measure the COF of native and GAG deficient cartilage at applied contact stress levels of 0.5 MPa, 2 MPa, and 3.15 MPa in 7h long friction tests with phosphate buffered saline (PBS) lubrication. The resultant deformation and wear of the cartilage samples due to the friction tests were measured using a height vernier apparatus and lubricant analysis respectively. An increase in contact stress from 0.5 MPa to 3.15 MPa resulted in an in...
Langmuir, 2014
Wear resistant and ultralow friction in synovial joints is the outcome of a sophisticated synergy between the major macromolecules of the synovial fluid, e.g., hyaluronan (HA) and proteoglycan 4 (PRG4), with collagen type II fibrils and other non-collagenous macromolecules of the cartilage superficial zone (SZ). This study aimed at better understanding the mechanism of PRG4 localization at the cartilage surface. We show direct interactions between surface bound HA and freely floating PRG4 using the quartz crystal microbalance with dissipation (QCM-D). Freely floating PRG4 was also shown to bind with surface bound collagen type II fibrils. Albumin, the most abundant protein of the synovial fluid, effectively blocked the adsorption of PRG4 with HA, through interaction with C and N terminals on PRG4, but not that of PRG4 with collagen type II fibrils. The above results indicate that collagen type II fibrils strongly contribute in keeping PRG4 in the SZ during cartilage articulation in situ. Furthermore, PRG4 molecules adsorbed very well on mimicked SZ of absorbed HA molecules with entangled collagen type II fibrils and albumin was not able to block this interaction. In this last condition PRG4 adsorption resulted in a coefficient of friction (COF) of the same order of magnitude as the COF of natural cartilage, measured with an atomic force microscope in lateral mode.
Association between friction and wear in diarthrodial joints lacking lubricin
Arthritis & Rheumatism, 2007
Objective. The glycoprotein lubricin (encoded by the gene Prg4) is secreted by surface chondrocytes and synovial cells, and has been shown to reduce friction in vitro. In contrast to man-made bearings, mammalian diarthrodial joints must endogenously produce frictionreducing agents. This study was undertaken to investigate whether friction is associated with wear. Methods. The lubricating ability of synovial fluid (SF) samples from humans with genetic lubricin deficiency was tested in vitro. The coefficient of friction in the knee joints of normal and lubricin-null mice was measured ex vivo; these joints were also studied by light and electron microscopy. Atomic force microscopy was used to image and measure how lubricin reduces friction in vitro. Results. SF lacking lubricin failed to reduce friction in the boundary mode. Joints of lubricin-null mice showed early wear and higher friction than joints from their wild-type counterparts. Lubricin self-organized and reduced the work of adhesion between apposing asperities. Conclusion. These data show that friction is coupled with wear at the cartilage surface in vivo. They imply that acquired lubricin degradation occurring in inflammatory joint diseases predisposes the cartilage to damage. Lastly, they suggest that lubricin, or similar biomolecules, will have applications in man-made devices in which reducing friction is essential.
Microscale surface friction of articular cartilage in early osteoarthritis
Journal of the Mechanical Behavior of Biomedical Materials, 2013
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 topmost 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 lubricinan important cartilage surface boundary lubricantdid 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.
Role of Serum Albumin Aggregation in Lubrication and Wear Protection of Shearing Surfaces
2019
Healthy articular joints exhibit remarkable lubrication due in large part to the complex rheological and tribological behavior of the synovial fluid (SF) that lubricates the joints. Current approaches that seek to elucidate such remarkable lubrication usually focus on the roles of high molecular weight SF components such as lubricin and hyaluronic acid but frequently overlook the role of serum albumin (SA), although it represents 90% of the protein content of SF. In this thesis, we used the Surface Forces Apparatus to investigate in detail the structural and tribological response of SA thin films when sheared between model surfaces and subjected to a large range of shearing parameters. Our data indicate that, under shear, SA films reproduce closely the shear response previously reported for SF, i.e., film thickening and formation of numerous long-lived aggregates accompanied by low friction and efficient surface protection against damage. More specifically, our detailed investigation of shear parameters reveals that (i) strong anchoring of SA to surfaces promotes the formation of large rod-like shaped aggregates that enable rolling friction and keep surfaces far apart, preventing damage, (ii) aggregation mechanism is irreversible, which makes aggregates long-lived (though mobile) in the contact, and (iii) aggregate formation only occur when SA was sheared above a 'critical' amplitude Ac and a critical shear velocity Vc. Collectively, our results provide experimental evidence of the role of globular proteins, such as SA, in lubrication and establish a correlation between shearing parameters, formation and stability of aggregates, low friction and wear protection. Although our findings are based on experiments involving rigid, nonporous surfaces hence can hardly be generalized to compliant and porous cartilage surfaces, they are applicable to other rigid tribosystems such as artificial joints and will certainly advance our understanding of joint implants' lubrication in SF mediated by protein aggregation, with implications for future design of artificial joints and therapeutic interventions.
ESDA2008-59146 TECHNIQUES FOR ASSESSMENT OF WEAR BETWEEN HUMAN CARTILAGE SURFACES Izhak Etsion a
2020
Osteoarthritis (OA) is a disease of joints, affecting a large number of people worldwide. One of the symptoms of OA is wear of articular cartilage; it is thought that among other factors this may be due to failure of lubrication. Injection of biolubricants into a joint may remedy this problem. Wear of cartilage and its prevention is a focus of much interest. The present paper describes wear tests performed using cartilage on cartilage under various working conditions. Several techniques assessing wear are described, such as changes in surface morphology using optical profilometry and variation in the concentration of proteoglycans (PG) and hydroxyproline in the lubricating solution.
Journal of Biomechanics, 2012
Boundary lubrication is characterized by sliding surfaces separated by a molecularly thin film that reduces friction and wear of the underlying substrate when fluid lubrication cannot be established. In this study, the wear and replenishment rates of articular cartilage were examined in the context of friction coefficient changes, protein loss, and direct imaging of the surface ultrastructure, to determine the efficiency of the boundary lubricant (BL) layer. Depletion of cartilage lubricity occurred with the concomitant loss of surface proteoglycans. Restoration of lubrication by incubation with synovial fluid was much faster than incubation with culture media and isolated superficial zone protein. The replenishment action of the BL layer in articular cartilage was rapid, with the rate of formation exceeding the rate of depletion of the BL layer to effectively protect the tissue from mechanical wear. The obtained results indicate that boundary lubrication in articular cartilage depends in part on a sacrificial layer mechanism. The present study provides insight into the natural mechanisms that minimize wear and resist tissue degeneration over the lifetime of an organism.