Material and functional properties of articular cartilage and patellofemoral contact mechanics in an experimental model of osteoarthritis

The purposes of this study were to determine the in situ functional and material properties of articular cartilage in an experimental model of joint injury, and to quantify the corresponding in situ joint contact mechanics. Experiments were performed in the anterior cruciate ligament (ACL) transected knee of the cat and the corresponding, intact contralateral knee, 16 weeks following intervention. Cartilage thickness, stiffness, effective Young’s modulus, and permeability were measured and derived from six locations of the knee. The total contact area and peak pressures in the patellofemoral joint were obtained in situ using Fuji Pressensor film, and comparisons between experimental and contralateral joint were made for corresponding loading conditions. Total joint contact area and peak pressure were increased and decreased significantly (=0.01), respectively, in the experimental compared to the contralateral joint. Articular cartilage thickness and stiffness were increased and decreased significantly (=0.01), respectively, in the experimental compared to the contralateral joint in the four femoral and patellar test locations. Articular cartilage material properties (effective Young’s modulus and permeability) were the same in the ACL-transected and intact joints. These results demonstrate for the first time the effect of changes in articular cartilage properties on the load transmission across a joint. They further demonstrate a substantial change in the joint contact mechanics within 16 weeks of ACL transection. The results were corroborated by theoretical analysis of the contact mechanics in the intact and ACL-transected knee using biphasic contact analysis and direct input of cartilage properties and joint surface geometry from the experimental animals. We conclude that the joint contact mechanics in the ACL-transected cat change within 16 weeks of experimental intervention.     

Load sharing between solid and fluid phases in articular cartilage: I--Experimental determination of in situ mechanical conditions in a porcine knee.

The in situ mechanical conditions of cartilage in the articulated knee were quantified during joint loading. Six porcine knees were subjected to a 445 N compressive load while cartilage deformations and contact pressures were measured. From roentgenograms, cartilage thickness before and during loading allowed the calculation of tissue deformation on the lateral femoral condyle at different times during the loading process. Contact pressures on the articular surface were measured with miniature fiber-optic pressure transducers. Results showed that the medial side of the lateral femoral condyle had higher contact pressures, as well as deformations. To begin to correlate the pressures and resulting deformations, the intrinsic material properties of the cartilage on the lateral condyle were obtained from indentation tests. Data from four normal control specimens indicated that the aggregate modulus of the medial side was significantly higher than in other areas of the condyle. These experimental measures of the in situ mechanical conditions of articular cartilage can be combined with theoretical modeling to obtain valuable information about the relative contributions of the solid and fluid phases to supporting the applied load on the cartilage surface (see Part II).     

Effect of superficial collagen patterns and fibrillation of femoral articular cartilage on knee joint mechanics-a 3D finite element analysis

Collagen fibrils of articular cartilage have specific depth-dependent orientations and the fibrils bend in the cartilage surface to exhibit split-lines. Fibrillation of superficial collagen takes place in osteoarthritis. We aimed to investigate the effect of superficial collagen fibril patterns and collagen fibrillation of cartilage on stresses and strains within a knee joint. A 3D finite element model of a knee joint with cartilage and menisci was constructed based on magnetic resonance imaging. The fibril-reinforced poroviscoelastic material properties with depth-dependent collagen orientations and split-line patterns were included in the model. The effects of joint loading on stresses and strains in cartilage with various split-line patterns and medial collagen fibrillation were simulated under axial impact loading of 1000 N. In the model, the collagen fibrils resisted strains along the split-line directions. This increased also stresses along the split-lines. On the contrary, contact and pore pressures were not affected by split-line patterns. Simulated medial osteoarthritis increased tissue strains in both medial and lateral femoral condyles, and contact and pore pressures in the lateral femoral condyle. This study highlights the importance of the collagen fibril organization, especially that indicated by split-line patterns, for the weight-bearing properties of articular cartilage. Osteoarthritic changes of cartilage in the medial femoral condyle created a possible failure point in the lateral femoral condyle. This study provides further evidence on the importance of the collagen fibril organization for the optimal function of articular cartilage.     

Biphasic indentation of articular cartilage--II. A numerical algorithm and an experimental study

Part I (Mak et al., 1987, J. Biomechanics 20, 703-714) presented the theoretical solutions for the biphasic indentation of articular cartilage under creep and stress-relaxation conditions. In this study, using the creep solution, we developed an efficient numerical algorithm to compute all three material coefficients of cartilage in situ on the joint surface from the indentation creep experiment. With this method we determined the average values of the aggregate modulus. Poisson's ratio and permeability for young bovine femoral condylar cartilage in situ to be HA = 0.90 MPa, vs = 0.39 and k = 0.44 x 10(-15) m4/Ns respectively, and those for patellar groove cartilage to be HA = 0.47 MPa, vs = 0.24, k = 1.42 x 10(-15) m4/Ns. One surprising finding from this study is that the in situ Poisson's ratio of cartilage (0.13-0.45) may be much less than those determined from measurements performed on excised osteochondral plugs (0.40-0.49) reported in the literature. We also found the permeability of patellar groove cartilage to be several times higher than femoral condyle cartilage. These findings may have important implications on understanding the functional behavior of cartilage in situ and on methods used to determine the elastic moduli of cartilage using the indentation experiments.     

Observation on the development of osteochondrosis in young rats

A histopathological study on the development of spontaneous osteochondrosis in the humeral head and medial femoral condyle of rats (6-20 weeks old) was carried out. Findings were classified into three types: normal, transitional and osteochondrotic. In the normal type, the articular cartilage at the caudal region of the humeral head and medial femoral condyle was significantly thinned between 6 and 10 weeks of age (generally the caudal region was thicker than elsewhere at all ages). In the transitional type, the thinning of the cartilage was delayed. In the third type, osteochondrotic lesions were detected in the humeral head from 6 weeks of age and in the medial femoral condyle from 10 weeks of age. The thickness of the cartilage had slightly decreased or had not changed at 20 weeks of age. In the early stages, viable chondrocytes and small destructive foci of cartilage were observed in the basal layer of the thick deep zone. These cells were present in pairs or clusters surrounded by matrix in the large lacunae. Cells and destructive foci were also seen in the surface layer of the deep zone as the rats aged. In the advanced stage, a necrotic area or cleft was formed in the basal layer of the articular cartilage and fibrosis was observed in the subchondral bone.     

Modeling of constrained articular cartilage growth in an intact knee with focal knee resurfacing metal implant

The purpose of the present study was to develop a model to simulate the articular cartilage growth in an intact knee model with a metal implant replacing a degenerated portion of the femoral cartilage. The human knee joint was approximated with a simplified axisymmetric shape of the femoral condyle along with the cartilage, meniscus and bones. Two individually growing constituents (proteoglycans and collagen) bound to solid matrix were considered in the solid phase of the cartilage. The cartilage behavior was modeled with a nonlinear biphasic porohyperelastic material model, and meniscus with a transversely isotropic linear biphasic poroelastic material model. Two criteria (permeation and shear), both driven by mechanical loading, were considered to trigger the growth in the solid constituents. Mechanical loading with sixty heavy cycles was considered to represent daily walking activity. The growth algorithm was implemented for 90 days after implantation. The results from simulations show that both cartilage layers were more stimulated near the implant which lead to more growth of the cartilage near the defect. The method developed in the present work could be a powerful technique if more accurate material data and growth laws were available.     

Osmotic loading to determine the intrinsic material properties of guinea pig knee cartilage

Few methods exist to study cartilage mechanics in small animal joints due to the difficulties associated with handling small tissue samples. In this study, we apply an osmotic loading method to quantify the intrinsic material properties of articular cartilage in small animal joints. Cartilage samples were studied from the femoral condyle and tibial plateau of two-month old guinea pigs. Swelling strains were measured using confocal fluorescence scanning microscopy in samples subjected to osmotic loading. A histochemical staining method was developed and calibrated for quantification of negative fixed charge density in guinea pig cartilage. Site-matched swelling strain data and fixed charge density values were then used with a triphasic theoretical model for cartilage swelling to determine the uniaxial modulus of the cartilage solid matrix. Moduli obtained in this study (7.2 MPa femoral condyle; 10.8 MPa, tibial plateau) compare well with previously reported values for the tensile moduli of human and other animal cartilages determined from uniaxial tension experiments. This study provides the first available data for material properties and fixed charge density in cartilage from the guinea pig knee and suggests a promising method for tracking changes in cartilage mechanics in small animal models of degeneration.     

Indentation stiffness of young canine knee articular cartilage—Influence of strenuous joint loading

The indentation stiffness of knee articular cartilage subjected to strenuous physical training (SPT: treadmill running 20 km day⁻¹ for 15 weeks, n = 6) of young Beagles was tested and compared to that obtained from age-matched (55 weeks, n = 9) controls. The mathematical solution for the shear modulus, as determined from indentation of an elastic layer bonded to a rigid half space, was extended to small Poisson's ratios and applied to the analysis of cartilage response after a step stress (0.39 MPa) application. In these measurements with an impervious, plane-ended indenter, the equilibrium deformation was systematically greater than values predicted from the instant response by the linear biphasic theory. Therefore, the accurate determination of Poisson's ratio from the creep curves was not possible. The mean shear modulus (calculated by using the deformation at 900 s after load application and assuming a constant Poisson's ratio of 0.40 for the matrix) of canine knee articular cartilage was 0.37 MPa. While the cartilage thickness was not affected by SPT, the cartilage of the lateral tibial plateau was stiffer (13.3%, p<0.05) than that in controls. However, in the femoral condyles, the stiffness was at the control level or even below. Our results on cartilage structure and properties suggest that SPT, in contrast to our previous findings with moderate training, does not necessarily improve the biological properties of articular cartilage in young animals.     

The acute effect of bipolar radiofrequency energy thermal chondroplasty on intrinsic biomechanical properties and thickness of chondromalacic human articular cartilage

Radio frequency energy (RFE) thermal chondroplasty has been a widely-utilized method of cartilage debridement in the past. Little is known regarding its effect on tissue mechanics. This study investigated the acute biomechanical effects of bipolar RFE treatment on human chondromalacic cartilage. Articular cartilage specimens were extracted (n?=?50) from femoral condyle samples of patients undergoing total knee arthroplasty. Chondromalacia was graded with the Outerbridge classification system. Tissue thicknesses were measured using a needle punch test. Specimens underwent pretreatment load-relaxation testing using a spherical indenter. Bipolar RFE treatment was applied for 45?s and the indentation protocol was repeated. Structural properties were derived from the force-time data. Mechanical properties were derived using a fibril-reinforced biphasic cartilage model. Statistics were performed using repeated measures ANOVA. Cartilage thickness decreased after RFE treatment from a mean of 2.61?mm to 2.20?mm in Grade II, II-III, and III specimens (P?相似文献   

Anisotropy and inter-condyle heterogeneity of cartilage under large-strain shear

We were the first to examine the mechanical responses of skeletally mature bovine femoral cartilage under large-strain simple shear (up to ±20%) using a multiaxial shear testing device. Since shear loading is critical in both tissue failure and chondrocyte responses, we aimed to probe (1) anisotropy with respect to the split-line direction (principal alignment of the collagen fibers near the articulating surface), (2) heterogeneity between femoral condyles, and (3) the influence of local cartilage thickness. We harvested a total of 48 cuboid cartilage specimens from four bovine knee joints. With each specimen we applied shear strains both parallel and perpendicular to the local split-line direction at a rate of 75 μm/min and calculated the peak-to-peak shear stresses, shear strain–energy dissipation densities, and peak effective shear moduli. The Wilcoxon signed rank test revealed that the medial condyle was anisotropic in some mechanical measures at applied shear strains above 5%, while the lateral condyle was mechanically isotropic at all applied shear strains. The Kruskal–Wallis test revealed no significant differences in the median mechanical behavior of the lateral and medial condyles. Spearman׳s rank correlations revealed statistically significant negative monotonic correlations among thickness and most of our mechanical measures for both lateral and medial condyles at most applied strains and directions of applied shear. These results suggest that large-strain analyses account for nonlinear, anisotropic and location-dependent effects not fully realized at small strains. Our findings may inspire new experiments and models that consider anisotropy and heterogeneity of cartilage in ways previously ignored.     

Investigation into the biphasic properties of a hydrogel for use in a cushion form replacement joint.

A hydrogel with potential applications in the role of a cushion form replacement joint bearing surface material has been investigated. The material properties are required for further development and design studies and have not previously been quantified. Creep indentation experiments were therefore performed on samples of the hydrogel. The biphasic model developed by Mow and co-workers (Mak et al., 1987; Mow et al., 1989a) was used to curve-fit the experimental data to theoretical solutions in order to extract the three intrinsic biphasic material properties of the hydrogel (aggregate modulus, HA, Poisson's ratio, Vs, and permeability, k). Ranges of material properties were determined: aggregate modulus was calculated to be between 18.4 and 27.5 MPa, Poisson's ratio 0.0-0.307, and permeability 0.012-7.27 x 10(-17) m4/Ns. The hydrogel thus had a higher aggregate modulus than values published for natural normal articular cartilage, the Poisson's ratios were similar to articular cartilage, and finally the hydrogel was found to be less permeable than articular cartilage. The determination of these values will facilitate further numerical analysis of the stress distribution in a cushion form replacement joint.     

Structural and functional changes of the articular surface in a post-traumatic model of early osteoarthritis measured by atomic force microscopy

The functional integrity of the articulating cartilage surface is a critical determinant of joint health. Although a variety of techniques exist to characterize the structural changes in the tissue with osteoarthritis (OA), some with extremely high resolution, most lack the ability to detect and monitor the functional changes that accompany the structural deterioration of this essential bearing surface. Atomic force microscopy (AFM) enables the acquisition of both structural and mechanical properties of the articular cartilage surface, with up to nanoscale resolution, making it particularly useful for evaluating the functional behavior of the macromolecular network forming the cartilage surface, which disintegrates in OA.In the present study, AFM was applied to the articular cartilage surfaces from six pairs of canine knee joints with post-traumatic OA. Microstructure (RMS roughness) and micromechanics (dynamic indentation modulus, E^?) of medial femoral condyle cartilages were compared between contralateral controls and cruciate-transected knee joints, which develop early signs of OA by three months after surgery.Results reveal a significant increase in RMS roughness and a significant four-fold decrease in E^? in cartilages from cruciate-transected joints versus contralateral controls. Compared to previous reports of changes in bulk mechanics, AFM was considerably more sensitive at detecting early cartilage changes due to cruciate-deficiency. The use of AFM in this study provides important new information on early changes in the natural history of OA because of its ability to sensitively detect and measure local structural and functional changes of the articular cartilage surface, the presumptive site of osteoarthritic initiation.     

Effects of increased chronic loading on articular cartilage material properties in the Lapine tibio-femoral joint

Methods of producing relevant and quantifiable load alterations in vivo with which to study load-induced cartilage degeneration analogous to osteoarthritis are limited. An animal model was used to investigate the effects of increased chronic loads on articular cartilage. Mature rabbits were randomized into one of three experimentally loaded groups and a fourth unoperated control group. A mechanical-loading device was skeletally fixed to the hind limb of animals in the loaded groups. Engaging the device resulted in an additional load of 0%, +22% or +44% body weight to the medial compartment of the experimental knee, while allowing normal joint function. Following a 12-week loading protocol, a creep-indentation test and needle probe test were used to determine the biphasic material properties and thickness of the cartilage at four locations of each femoral and tibial condyle of the experimental and contralateral limbs. Analyses of covariance were performed to compare outcome measures across the treatment groups. The effect of increased load was site and load-level specific with alterations of material properties and thickness most prominent in the posterior region of the medial compartment of the tibia. At this site, permeability increased 128% and thickness increased 28% in the +44% body weight group relative to the 0% body weight group. This model of altered chronic loading initiated changes in the material properties to the articular cartilage at the sites of increased load over 12-weeks that were consistent with early degenerative changes suggesting that increased tibio-femoral loading may be responsible for the alterations. This work begins to elucidate the chronic-load threshold and the time course of cartilage degeneration at different levels of altered loading.     

Experimental determination of the linear biphasic constitutive coefficients of human fetal proximal femoral chondroepiphysis

The mechanical properties of the cartilaginous regions of the proximal femoral epiphysis are an important factor in load transmission through the hip joint of young children. Cylindrical test specimens excised from the chondroepiphysis of human stillborn femoral heads were subjected to uniaxial loading in peripherally-unconfined compression, using a ramp/plateau input strain history. The corresponding load vs time curves were analyzed in terms of a recent analytical solution for a linear biphasic material (the well-known KLM model), allowing calculation of that model's three fundamental constitutive coefficients (permeability, equilibrium modulus and solid-phase Poisson ratio) for this material. The numerical algorithm developed to evaluate the biphasic solution yielded very precise replication of previously published KLM parametric plots. When fitted to experimental load histories, however, the model provided only a rather loose approximation of specimen behavior, due apparently to a substantial underestimation of the transient response component associated with interstitial fluid transport. Averaged over the series, the best-fit values for permeability (2.51 X 10(-15) m4 Ns-1) and equilibrium modulus (0.699 MPa) were in the range of values accepted for human adult articular cartilage. A consequence of the coarseness of the analytical curve fits was that a solid-phase Poisson ratio of 0.0 was inferred for all specimens. The permeability vs equilibrium modulus exhibited a nearly linear (r = 0.74) inverse relationship similar to that reported for adult articular cartilage.     

Interrelationship of cartilage composition and chondrocyte mechanics after a partial meniscectomy in the rabbit knee joint – Experimental and numerical analysis

Site-specific and depth-dependent properties of cartilage were implemented within a finite element (FE) model to determine if compositional or structural changes in the tissue could explain site-specific alterations of chondrocyte deformations due to cartilage loading in rabbit knee joints 3 days after a partial meniscectomy (PM). Depth-dependent proteoglycan (PG) content, collagen content and collagen orientation in the cartilage extracellular matrix (ECM), and PG content in the pericellular matrix (PCM) were assessed with microscopic and spectroscopic methods. Patellar, femoral groove and samples from both the lateral and medial compartments of the femoral condyle and tibial plateau were extracted from healthy controls and from the partial meniscectomy group. For both groups and each knee joint site, axisymmetric FE models with measured properties were generated. Experimental cartilage loading was applied in the simulations and chondrocyte volumes were compared to the experimental values. ECM and PCM PG loss occurred within the superficial cartilage layer in the PM group at all locations, except in the lateral tibial plateau. Collagen content and orientation were not significantly altered due to the PM. The FE simulations predicted similar chondrocyte volume changes and group differences as obtained experimentally. Loss of PCM fixed charge density (FCD) decreased cell volume loss, as observed in the medial femur and medial tibia, whereas loss of ECM FCD increased cell volume loss, as seen in the patella, femoral groove and lateral femur. The model outcome, cell volume change, was also sensitive to applied tissue geometry, collagen fibril orientation and loading conditions.     

Regional differences of tibial and femoral cartilage in the chondrocyte gene expression,immunhistochemistry and composite in different stages of osteoarthritis

The function of articular cartilage as an avascular tissue is mainly served by collagen type II and proteoglycan molecules. Within this matrix homeostasis between production and breakdown of the matrix is exceptionally sensitive.The current study was conducted to identify regional differences in specific alterations in cartilage composition during the osteoarthritic process of the human knee joint. Therefor the changes in the expression of the key molecules of the extracellular matrix were measured in dependence of the anatomical side (femoral vs tibial) and associated with immunohistochemistry and quantitative measurement.60 serial osteochondral femoral condyle and the tibial plateau samples of patients undergoing implantation of total knee endoprosthesis of areas showing mild (Group A, macroscopically ICRS grade 1b) respectively advanced (Group B, macroscopically ICRS grade 3a/3b) (30 each) osteoarthritis according to the histological-histochemical grading system (HHGS) were compared with 20 healthy biopsies with immunohistochemistry and histology. We quantified our results on the gene expression of collagen type I and II and aggrecan with the help of real-time (RT)-PCR. Proteoglycan content was measured colorometrically.In group A slightly increased colour intensity was found for collagen II in deeper layers, suggesting a persisting but initially still intact repair process. But especially on the medial tibia plateau the initial Col II increase in gene expression is followed by a decrease leading to the lowest over all Col II expression on the medial plateau, here especially in the central part. There in late stage diseases the collagen type I expression was also more pronounced. Markedly decreased safranin O staining intensity was observed in the radial zone and less reduced intensity in the transitional zone with loss of zonal anatomy in 40% of the specimens in group A and all specimens in group B. Correlation between colorometrically analysed proteoglycan GAG content and aggrecan Real Time PCR is mainly weak.Tibial and femoral cartilage in contrast to patellar cartilage both are preferential exposed to compressive stresses, but presence of menisci affects the load distribution at the tibial side, which creates varying conditions for the different cartilage surfaces in the knee.As directly measured Poissońs ratio in tibial cartilage is higher but Youn?s modulus is lower than in femoral cartilage, different resulting feedback amplification loops interact with proceeding cartilage damage. The initial loss of aggrecan may support Matrix metalloproteinases (Mmps) in the access to the collagen network and the considerably differing mechanical properties at both joint surfaces result in varying increased synthesis and release of matrix degrading enzymes.The present study has identified a selection of events which reflect the response of cartilage structure and composite, chondrocytes itself and their productivity to changes in mechanical stress depending on the anatomical site.     

Precision MRI-based joint surface and cartilage density analysis of the knee joint using rapid water-excitation sequence and semi-automatic segmentation algorithm]

The aim of this study was to analyse the precision of three-dimensional joint surface and cartilage thickness measurements in the knee, using a fast, high-resolution water-excitation sequence and a semiautomated segmentation algorithm. The knee joint of 8 healthy volunteers, aged 22 to 29 years, were examined at a resolution of 1.5 mm x 0.31 mm x 0.31 mm, with four sagittal data sets being acquired after repositioning the joint. After semiautomated segmentation with a B-spline Snake algorithm and 3D reconstruction of the patellar, femoral and tibial cartilages, the joint surface areas (triangulation), cartilage volume, and mean and maximum thickness (Euclidean distance transformation) were analysed, independently of the orientation of the sections. The precision (CV%) for the surface areas was 2.1 to 6.6%. The mean cartilage thickness and cartilage volume showed coefficients of 1.9 to 3.5% (except for the femoral condyles), the value for the medial femoral condyle being 9.1%, and for the lateral condyle 6.5%. For maximum thickness, coefficients of between 2.6 and 5.9% were found. In the present study we investigate for the first time the precision of MRI-based joint surface area measurements in the knee, and of cartilage thickness analyses in the femur. Using a selective water-excitation sequence, the acquisition time can be reduced by more than 50%. The poorer precision in the femoral condyles can be attributed to partial volume effects that occur at the edges of the joint surfaces with a sagittal image protocol. Since MRI is non-invasive, it is highly suitable for examination of healthy subjects (generation of individual finite element models, analysis of functional adaptation to mechanical stimulation, measurement of cartilage deformation in vivo) and as a diagnostic tool for follow-up, indication for therapy, and objective evaluation of new therapeutic agents in osteoarthritis.     

Age-related changes in the tensile properties of human articular cartilage: a comparative study between the femoral head of the hip joint and the talus of the ankle joint

Specimens of articular cartilage from the superficial and mid-depth zones of the human femoral head and the talus of the ankle joint were tested in tension in planes parallel to the articular surface and parallel to the predominant orientation of the superficial collagen fibrils. The tensile fracture stress of cartilage from both the superficial and mid-depth zones of the femoral head decreased considerably with age. The superficial zone decreased from 33 MPa at 7 years to 10 MPa by the age of 90 years, while the mid-depth zone decreased from 32 MPa at 7 years to 2 MPa by the age of 85 years. In contrast the fracture stress of both levels of cartilage from the talus of the ankle did not decrease significantly with increasing age. The tensile stiffness at 10 MPa of both the superficial and mid-depth zones of the femoral head decreased with age. That of the superficial zone decreased from 150 MPa at 7 years to 80 MPa at 90 years, while the mid-depth zone decreased from 60 MPa at 7 years to 10 MPa at 60 years. The stiffness of talar cartilage from the superficial zone decreased by 20%, while that of the mid-depth zone showed a slight increase in stiffness at 10 MPa with increasing age. There was no significant decrease in the tensile stiffness at 1 MPa with age for either the femoral head or talar cartilage. Based on the results of previous studies it is possible to conclude that the decrease in tensile properties seen in the femoral head results from a deterioration in the tensile properties of the network of collagen fibrils. It is suggested that progressive fatigue failure, perhaps with associated changes in the structure of cartilage due to altered chondrocyte metabolism, causes the reduction in tensile properties with age. The results offer a potential explanation for the observation that osteoarthritis commonly occurs in the hip and knee joints at an increasing incidence as age increases, while the condition only rarely occurs in the ankle joint except as a secondary event to trauma.     

Poly(vinyl alcohol) hydrogel as a biocompatible viscoelastic mimetic for articular cartilage

The prevalence of suboptimal outcome for surgical interventions in the treatment of full-thickness articular cartilage damage suggests that there is scope for a materials-based strategy to deliver a more durable repair. Given that the superficial layer of articular cartilage creates and sustains the tribological function of synovial joints, it is logical that candidate materials should have surface viscoelastic properties that mimic native articular cartilage. The present paper describes force spectroscopy analysis by nano-indentation to measure the elastic modulus of the surface of a novel poly(vinyl alcohol) hydrogel with therapeutic potential as a joint implant. More than 1 order of magnitude decrease in the elastic modulus was detected after adsorption of a hyaluronic acid layer onto the hydrogel, bringing it very close to previously reported values for articular cartilage. Covalent derivatization of the hydrogel surface with fibronectin facilitated the adhesion and growth of cultured rat tibial condyle chondrocytes as evidenced morphologically and by the observance of metachromatic staining with toluidine blue dye. The present results indicate that hydrogel materials with potential therapeutic benefit for injured and diseased joints can be engineered with surfaces with biomechanical properties similar to those of native tissue and are accepted as such by their constituent cell type.