Biomedical subjects

Gerard A Ateshian

Publications and source records attributed to Gerard A Ateshian.

9 recordsLinked to original sources

PubMed2003

Optical determination of anisotropic material properties of bovine articular cartilage in compression.

The precise nature of the material symmetry of articular cartilage in compression remains to be elucidated. The primary objective of this study was to determine the equilibrium compressive Young's moduli and Poisson's ratios of bovine cartilage along multiple directions (parallel and perpendicular to the split line direction, and normal to the articular surface) by loading small cubic specimens (0.9 x 0.9 x 0.8 mm, n =15) in unconfined compression, with the expectation that the material symmetry of cartilage could be determined more accurately with the help of a more complete set of material properties. The second objective was to investigate how the tension-compression nonlinearity of cartilage might alter the interpretation of material symmetry. Optimized digital image correlation was used to accurately determine the resultant strain fields within the specimens under loading. Experimental results demonstrated that neither the Young's moduli nor the Poisson's ratios exhibit the same values when measured along the three loading directions. The main findings of this study are that the framework of linear orthotropic elasticity (as well as higher symmetries of linear elasticity) is not suitable to describe the equilibrium response of articular cartilage nor characterize its material symmetry; a framework which accounts for the distinctly different responses of cartilage in tension and compression is more suitable for describing the equilibrium response of cartilage; within this framework, cartilage exhibits no lower than orthotropic symmetry.

Animals↗

PubMed2003

Sequential wear patterns of the articular cartilage of the thumb carpometacarpal joint in osteoarthritis.

PURPOSE: The thumb carpometacarpal (CMC) joint is a primary location for osteoarthritis (OA) in the body; however, articular cartilage thickness distribution during progression of OA in the joint has not been reported previously. Determining the cartilage wear patterns within the joint is important in understanding the etiology and treatment of thumb CMC joint OA. This study used cadaveric specimens to investigate the wear patters of the articular surfaces of the trapezium and thumb metacarpal. METHODS: A total of 104 fresh-frozen thumb CMC joints were radiographed, disarticulated, and visually staged for OA. Cartilage thickness maps of the trapezium and metacarpal were determined for each joint by using stereophotogrammetry. Average cartilage thickness maps for the trapezium and metacarpal were generated from all specimens for each of 4 stages of OA, showing the progression of cartilage thickness changes with disease. RESULTS: In normal joints, the surface-wide mean thickness of the articular layers is 0.8 +/- 0.2 mm for the trapezium and 0.7 +/- 0.2 mm for the metacarpal. The average thickness maps were analyzed by anatomic quadrant (dorsal-radial, dorsal-ulnar, volar-radial, volar-ulnar) within the 4 stages of OA. Corresponding quadrants also were compared across the increasing stages of OA. Results show that cartilage degradation is initiated in the radial quadrants of the metacarpal and progresses to the volar quadrants of the articular surface, while significant wear is seen on the dorsal-radial quadrant of the trapezium and progresses to the volar quadrants in late-stage osteoarthritis. CONCLUSIONS: These quantitative results on cartilage thinning agree with previous investigators' reports of high load bearing and low load bearing areas in the CMC joint during functional pinch and grasp positions. Understanding the progression of OA in the thumb CMC joint may aid in the surgical treatment of this disease.

Adolescent↗

PubMed2003

Synergistic action of growth factors and dynamic loading for articular cartilage tissue engineering.

It has previously been demonstrated that dynamic deformational loading of chondrocyte-seeded agarose hydrogels over the course of 1 month can increase construct mechanical and biochemical properties relative to free-swelling controls. The present study examines the manner in which two mediators of matrix biosynthesis, the growth factors TGF-beta1 and IGF-I, interact with applied dynamic deformational loading. Under free-swelling conditions in control medium (C), the [proteoglycan content][collagen content][equilibrium aggregate modulus] of cell-laden (10 x 10(6) cells/mL) 2% agarose constructs reached a peak of [0.54% wet weight (ww)][0.16% ww][13.4 kPa]c, whereas the addition of TGF-beta1 or IGF-I to the control medium led to significantly higher peaks of [1.18% ww][0.97% ww][23.6 kPa](C-TGF) and [1.00% ww][0.63% ww][19.3 kPa](C-IGF), respectively, by day 28 or 35 (p<0.01). Under dynamic loading in control medium (L), the measured parameters were [1.10% ww][0.52% ww][24.5 kPa]L, and with the addition of TGF-beta1 or IGF-I to the control medium these further increased to [1.49% ww][1.07% ww][50.5 kPa](L-TGF) and [1.48% ww][0.81% ww][46.2 kPa](L-IGF), respectively (p<0.05). Immunohistochemical staining revealed that type II collagen accumulated primarily in the pericellular area under free-swelling conditions, but spanned the entire tissue in dynamically loaded constructs. Applied in concert, dynamic deformational loading and TGF-beta1 or IGF-I increased the aggregate modulus of engineered constructs by 277 or 245%, respectively, an increase greater than the sum of either stimulus applied alone. These results support the hypothesis that the combination of chemical and mechanical promoters of matrix biosynthesis can optimize the growth of tissue-engineered cartilage constructs.

Animals↗

PubMed2003

Experimental verification of the roles of intrinsic matrix viscoelasticity and tension-compression nonlinearity in the biphasic response of cartilage.

A biphasic-CLE-QLV model proposed in our recent study [2001, J. Biomech. Eng., 123, pp. 410-417] extended the biphasic theory of Mow et al. [1980, J. Biomech. Eng., 102, pp. 73-84] to include both tension-compression nonlinearity and intrinsic viscoelasticity of the cartilage solid matrix by incorporating it with the conewise linear elasticity (CLE) model [1995, J. Elasticity, 37, pp. 1-38] and the quasi-linear viscoelasticity (QLV) model [Biomechanics: Its foundations and objectives, Prentice Hall, Englewood Cliffs, 1972]. This model demonstrates that a simultaneous prediction of compression and tension experiments of articular cartilage, under stress-relaxation and dynamic loading, can be achieved when properly taking into account both flow-dependent and flow-independent viscoelastic effects, as well as tension-compression nonlinearity. The objective of this study is to directly test this biphasic-CLE-QLV model against experimental data from unconfined compression stress-relaxation tests at slow and fast strain rates as well as dynamic loading. Twelve full-thickness cartilage cylindrical plugs were harvested from six bovine glenohumeral joints and multiple confined and unconfined compression stress-relaxation tests were performed on each specimen. The material properties of specimens were determined by curve-fitting the experimental results from the confined and unconfined compression stress relaxation tests. The findings of this study demonstrate that the biphasic-CLE-QLV model is able to describe the strain-rate-dependent mechanical behaviors of articular cartilage in unconfined compression as attested by good agreements between experimental and theoretical curvefits (r2 = 0.966 +/- 0.032 for testing at slow strain rate; r2 = 0.998 +/- 0.002 for testing at fast strain rate) and predictions of the dynamic response (r2 = 0.91 +/- 0.06). This experimental study also provides supporting evidence for the hypothesis that both tension-compression nonlinearity and intrinsic viscoelasticity of the solid matrix of cartilage are necessary for modeling the transient and equilibrium responses of this tissue in tension and compression. Furthermore, the biphasic-CLE-QLV model can produce better predictions of the dynamic modulus of cartilage in unconfined dynamic compression than the biphasic-CLE and biphasic poroviscoelastic models, indicating that intrinsic viscoelasticity and tension-compression nonlinearity of articular cartilage may play important roles in the load-support mechanism of cartilage under physiologic loading.

Animals↗

PubMed2002

Influence of seeding density and dynamic deformational loading on the developing structure/function relationships of chondrocyte-seeded agarose hydrogels.

Chondrocytes cultured in agarose hydrogels develop a functional extracellular matrix. Application of dynamic strain at physiologic levels to these constructs over time can increase their mechanical properties. In this study, the effect of seeding density (20 and 60 x 10(6) cells/ml) on tissue elaboration was investigated. Higher seeding densities increased tissue properties in free-swelling culture, with constructs seeded at 20 and 60 x 10(6) cells/ml reaching maximum values over the 63 day culture period of aggregate modulus HA: 43 +/- 15 kPa, Young's modulus EY: 39 +/- 3 kPa, and glycosaminglycan content [GAG]: 0.96% +/- 0.13% wet weight; and HA: 58 +/- 12 kPa, EY: 60 +/- 5 kPa, and [GAG]: 1.49% +/- 0.26% wet weight, respectively. It was further observed that the application of daily dynamic deformational loading to constructs seeded at 20 x 10(6) cells/ml enhanced biochemical content (approximately 150%) and mechanical properties (approximately threefold) compared to free-swelling controls by day 28. However, at a concentration of 60 x 10(6) cells/ml, no difference in mechanical properties was found in loaded samples versus their free-swelling controls. Multiple regression analysis showed that the mechanical properties of the tissue constructs depend more strongly on collagen content than GAG content; a finding that is more pronounced with the application of daily dynamic deformational loading. Our findings provide evidence for initial cell seeding density and nutrient accessibility as important parameters in modulating tissue development of engineered constructs, and their ability to respond to a defined mechanical stimulus.

Animals↗

PubMed2002

An automated approach for direct measurement of two-dimensional strain distributions within articular cartilage under unconfined compression.

An automated approachfor measuring in situ two-dimensional strain fields was developed and validated for its application to cartilage mechanics. This approach combines video microscopy, optimized digital image correlation (DIC), thin-plate spline smoothing (TPSS) and generalized cross-validation (GCV) techniques to achieve the desired efficiency and accuracy. Results demonstrate that sub-pixel accuracies can be achieved for measuring tissue displacements with this methodology with a measurement uncertainty ranging from 0.25 to 0.30 pixels. The deformational gradients (from which the strains are determined) can be evaluated directly using the optimized DIC, with a measurement uncertainty of 0.017 to approximately 0.032. In actual measurements of strain in cartilage, TPSS and differentiation can be used to achieve a more accurate measurement of the gradients from the displacement data. Using this automated approach, the two-dimensional strain fields inside immature bovine carpometacarpal joint cartilage specimens under unconfined compression were characterized (n=21). The depth-dependent apparent elastic modulus and Poisson's ratio were also determined and found to be smallest at the articular surface and increasing with depth. The apparent Poisson's ratio is found to decrease with increasing compressive strain, with values as low as 0.01 observed near the articular surface at 25% compression. The variation of the apparent Poisson's ratio with depth is found to be consistent with a theoretical model of cartilage which accounts for the disparity in its tensile and compressive moduli.

Animals↗

PubMed2002

The functional environment of chondrocytes within cartilage subjected to compressive loading: a theoretical and experimental approach.

A non-invasive methodology (based on video microscopy, optimized digital image correlation and thin plate spline smoothing technique) has been developed to determine the intrinsic tissue stiffness (H(a)) and the intrinsic fixed charge density (c(0)(F)) distribution for hydrated soft tissues such as articular cartilage. Using this technique, the depth-dependent inhomogeneous parameters H(a)(z) and c(0)(F)(z) were determined for young bovine cartilage and incorporated into a triphasic mixture model. This model was then used to predict the mechanical and electrochemical events (stress, strain, fluid/osmotic pressure, and electrical potentials) inside the tissue specimen under a confined compression stress relaxation test. The integration of experimental measurements with theoretical analyses can help to understand the unique material behaviors of articular cartilage. Coupled with biological assays of cell-scale biosynthesis, there is also a great potential in the future to study chondrocyte mechanotransduction in situ with a new level of specificity.

Animals↗

PubMedDate not supplied

Computer simulations of patellofemoral joint surgery. Patient-specific models for tuberosity transfer.

BACKGROUND: Variable clinical outcomes of tibial tuberosity transfer surgery have been reported. HYPOTHESES: The biomechanical outcome of surgery is patient-specific; no single procedure produces superior results for all patients. Use of patient-specific computer models can optimize choice of procedure. STUDY DESIGN: Computer simulation study using clinical data. METHODS: We used patient-specific multibody models of the patellofemoral joints of 20 patients with a diagnosis of patellar subluxation and osteoarthritis. Four tibial tuberosity transfer procedures (two anterior and two anteromedial) were simulated for each patient and compared with their preoperative model. RESULTS: When results for all patients were averaged, all simulated operations produced a statistically significant decrease in surface-wide mean contact stress, although no significant difference was found among them. CONCLUSIONS: The simulated surgical outcomes were patient-specific: no single procedure was consistently superior at decreasing peak or mean stress and each procedure produced a potentially detrimental outcome, an increase in either mean stress or peak stress, in at least one patient. CLINICAL RELEVANCE: Computer simulation may serve as a valuable tool for tailoring procedures to specific patients.

Biomechanical Phenomena↗

PubMedDate not supplied

Codominance of the individual posterior cruciate ligament bundles. An analysis of bundle lengths and orientation.

BACKGROUND: It is unclear how each bundle of the posterior cruciate ligament contributes to posterior knee stability. HYPOTHESIS: Changes in bundle orientation and length occur such that neither bundle dominates in restraining posterior tibial motion throughout knee flexion and extension. STUDY DESIGN: Controlled laboratory study. METHODS: Six fresh-frozen cadaveric knees were studied in a joint-testing rig with individual quadriceps and hamstring muscle loading. Kinematic data for the tibia and femur were obtained at knee flexion angles from 0 degrees to 120 degrees. The joint was then disarticulated, and the insertions of the two bundles on the tibia and femur were digitized. RESULTS: Length of the anterolateral bundle increased with increasing knee flexion angle from 10 degrees to 120 degrees. Length of the posteromedial bundle decreased with increasing knee flexion angle from 0 degrees to 45 degrees and increased slightly from 60 degrees to 120 degrees. Length of the anteromedial bundle was significantly less than that of the posteromedial at 0 degrees, 10 degrees, and 20 degrees of knee flexion. The anterolateral bundle was significantly more horizontal at flexion angles of 0 degrees, 10 degrees, 20 degrees, 30 degrees, and 45 degrees (P < 0.05). The posteromedial bundle was more horizontal at 120 degrees. CONCLUSIONS: Changes in orientation take place such that neither bundle dominates in restraining posterior tibial motion throughout knee flexion and extension. CLINICAL RELEVANCE: Double-bundle reconstructions achieve more physiologic knee function.

Aged↗