Biomedical subjects

Gerard A Ateshian

Publications and source records attributed to Gerard A Ateshian.

At least 19 recordsLinked to original sources

PubMed2006

Spatially varying material properties of the rat caudal intervertebral disc.

STUDY DESIGN: The use of a microscopy based material testing technique to assess the local material properties of rat caudal intervertebral discs under uniaxial compression. OBJECTIVES: To better understand the cell environment of rat caudal intervertebral discs during mechanical loading and elucidate better the role of the nucleus pulposus to the overall disc material properties. SUMMARY OF BACKGROUND DATA: Rat tail models of disc degeneration have been widely used for their similarity with the degeneration phenomena in human beings. Degenerative patterns in the disc are often inhomogeneous, however, only average material properties of rodent discs have been studied. Knowledge of the spatially varying properties within the disc is necessary to understand the disc cell milieu during tissue loading. METHODS: Rat caudal motion segments were tested intact, sectioned, and with alterations of nucleus pulposus using microscopy based techniques. Local displacements and strains were obtained using digital image correlation. Strains and load measurements were used to get the average apparent Young's modulus, peak stress, local Young's modulus, and local Poisson's ratio. RESULTS: There was no difference observed in the average apparent Young's modulus among experimental groups. Peak stresses decreased significantly when the nucleus pulposus was replaced with extremely fluid-like materials. The axial displacement field showed 3 distinct linear distributions in samples which were sectioned. The center region in all groups had significantly smaller axial strain and showed a higher local Young's modulus. CONCLUSIONS: The average equilibrium Young's modulus may be dependent on short-range ultrastructural organization. Spatially varying material properties within the intervertebral disc may be caused by orientation of fiber bundles in the different regions of the anulus fibrosus. The fiber bundles are better able to resist compressive loads when oriented parallel rather than perpendicular to the loading direction. At equilibrium, the anulus fibrosus also appears to have a shielding effect independent of the material filling up the nucleus pulposus space.

Animals↗

PubMed2006

A mixture theory analysis for passive transport in osmotic loading of cells.

The theory of mixtures is applied to the analysis of the passive response of cells to osmotic loading with neutrally charged solutes. The formulation, which is derived for multiple solute species, incorporates partition coefficients for the solutes in the cytoplasm relative to the external solution, and accounts for cell membrane tension. The mixture formulation provides an explicit dependence of the hydraulic conductivity of the cell membrane on the concentration of permeating solutes. The resulting equations are shown to reduce to the classical equations of Kedem and Katchalsky in the limit when the membrane tension is equal to zero and the solute partition coefficient in the cytoplasm is equal to unity. Numerical simulations demonstrate that the concentration-dependence of the hydraulic conductivity is not negligible; the volume response to osmotic loading is very sensitive to the partition coefficient of the solute in the cytoplasm, which controls the magnitude of cell volume recovery; and the volume response is sensitive to the magnitude of cell membrane tension. Deviations of the Boyle-van't Hoff response from a straight line under hypo-osmotic loading may be indicative of cell membrane tension.

Biological Transport↗

PubMed2006

Frictional response of bovine articular cartilage under creep loading following proteoglycan digestion with chondroitinase ABC.

The specific aim of this study was to investigate the effect of chondroitinase ABC treatment on the frictional response of bovine articular cartilage against glass, under creep loading. The hypothesis is that chondroitinase ABC treatment increases the friction coefficient of bovine articular cartilage under creep. Articular cartilage samples (n = 12) harvested from two bovine knee joints (1-3 months old) were divided into a control group (intact specimens) and a treated group (chondroitinase ABC digestion), and tested in unconfined compression with simultaneous continuous sliding (+/- 4 mm at 1 mm/s) under a constant applied stress of 0.5 MPa, for 2500 s. The time-dependent response of the friction coefficient was measured. With increasing duration of loading, treated samples exhibited a significantly higher friction coefficient than control samples as assessed by the equilibrium value (treated: micro(eq) = 0.19 +/- 0.02; control: micro(eq) = 0.12 +/- 0.03; p = 0.002), though the coefficient achieved immediately upon loading did not increase significantly (treated: micro(min) = 0.0053 +/- 0.0025; control: micro(min) = 0.037 +/- 0.0013; p = 0.19). Our results demonstrate that removal of the cartilage glycosaminoglycans using chondroitinase ABC significantly increases the overall time-dependent friction coefficient of articular cartilage. These findings strengthen the motivation for developing chondroprotective strategies by increasing cartilage chondroitin sulfate content in osteoarthritic joints.

Animals↗

PubMed2006

Dynamic response of immature bovine articular cartilage in tension and compression, and nonlinear viscoelastic modeling of the tensile response.

Very limited information is currently available on the constitutive modeling of the tensile response of articular cartilage and its dynamic modulus at various loading frequencies. The objectives of this study were to (1) formulate and experimentally validate a constitutive model for the intrinsic viscoelasticity of cartilage in tension, (2) confirm the hypothesis that energy dissipation in tension is less than in compression at various loading frequencies, and (3) test the hypothesis that the dynamic modulus of cartilage in unconfined compression is dependent upon the dynamic tensile modulus. Experiment 1: Immature bovine articular cartilage samples were tested in tensile stress relaxation and cyclical loading. A proposed reduced relaxation function was fitted to the stress-relaxation response and the resulting material coefficients were used to predict the response to cyclical loading. Adjoining tissue samples were tested in unconfined compression stress relaxation and cyclical loading. Experiment 2: Tensile stress relaxation experiments were performed at varying strains to explore the strain-dependence of the viscoelastic response. The proposed relaxation function successfully fit the experimental tensile stress-relaxation response, with R2 = 0.970+/-0.019 at 1% strain and R2 = 0.992+/-0.007 at 2% strain. The predicted cyclical response agreed well with experimental measurements, particularly for the dynamic modulus at various frequencies. The relaxation function, measured from 2% to 10% strain, was found to be strain dependent, indicating that cartilage is nonlinearly viscoelastic in tension. Under dynamic loading, the tensile modulus at 10 Hz was approximately 2.3 times the value of the equilibrium modulus. In contrast, the dynamic stiffening ratio in unconfined compression was approximately 24. The energy dissipation in tension was found to be significantly smaller than in compression (dynamic phase angle of 16.7+/-7.4 deg versus 53.5+/-12.8 deg at 10(-3) Hz). A very strong linear correlation was observed between the dynamic tensile and dynamic compressive moduli at various frequencies (R2 = 0.908+/-0.100). The tensile response of cartilage is nonlinearly viscoelastic, with the relaxation response varying with strain. A proposed constitutive relation for the tensile response was successfully validated. The frequency response of the tensile modulus of cartilage was reported for the first time. Results emphasize that fluid-flow dependent viscoelasticity dominates the compressive response of cartilage, whereas intrinsic solid matrix viscoelasticity dominates the tensile response. Yet the dynamic compressive modulus of cartilage is critically dependent upon elevated values of the dynamic tensile modulus.

Animals↗

PubMed2005

Spatial and temporal development of chondrocyte-seeded agarose constructs in free-swelling and dynamically loaded cultures.

Dynamic deformational loading has been shown to significantly increase the development of material properties of chondrocyte-seeded agarose hydrogels, however little is known about the spatial development of the material properties within these constructs. In this study, a technique that combines video microscopy and optimized digital image correlation, was applied to assess the spatial development of material properties in tissue-engineered cartilage constructs cultured in free-swelling and dynamically-loaded conditions (3h/day, 5 days/week, and maintained in free-swelling conditions when not being loaded) over a 6-week period. Although homogeneous at day 0, both free-swelling and dynamically loaded samples progressively developed stiffer outer edges and a softer central region. The distribution of GAGs and collagens were shown to mimic this profile. These results indicate that although dynamic loading augments the development of bulk properties in these samples, possibly by overcoming some of the diffusion limitation and nutrient transport issues, the overall profile of construct properties in the axial direction remains qualitatively the same as in free-swelling culture conditions. Poisson's ratio of these constructs increased over time in culture with increased fixed charged density contributed by the GAGs, but this increase was significantly less in dynamically loaded samples by day 42. Polarized light microscopy of Picrosirius Red labeled samples, at an angle perpendicular to the direction of loading, suggests that these differences in Poisson's ratio may be due to improved organization of collagen network in the dynamically loaded samples.

Animals↗

PubMed2005

Direct measurement of osmotic pressure of glycosaminoglycan solutions by membrane osmometry at room temperature.

Articular cartilage is a hydrated soft tissue composed of negatively charged proteoglycans fixed within a collagen matrix. This charge gradient causes the tissue to imbibe water and swell, creating a net osmotic pressure that enhances the tissue's ability to bear load. In this study we designed and utilized an apparatus for directly measuring the osmotic pressure of chondroitin sulfate, the primary glycosaminoglycan found in articular cartilage, in solution with varying bathing ionic strength (0.015 M, 0.15 M, 0.5 M, 1 M, and 2 M NaCl) at room temperature. The osmotic pressure (pi) was found to increase nonlinearly with increasing chondroitin sulfate concentration and decreasing NaCl ionic bath environment. Above 1 M NaCl, pi changes negligibly with further increases in salt concentration, suggesting that Donnan osmotic pressure is negligible above this threshold, and the resulting pressure is attributed to configurational entropy. Results of the current study were also used to estimate the contribution of osmotic pressure to the stiffness of cartilage based on theoretical and experimental considerations. Our findings indicate that the osmotic pressure resulting from configurational entropy is much smaller in cartilage (based on an earlier study on bovine articular cartilage) than in free solution. The rate of change of osmotic pressure with compressive strain is found to contribute approximately one-third of the compressive modulus (H(A)(eff)) of cartilage (Pi approximately H(A)(eff)/3), with the balance contributed by the intrinsic structural modulus of the solid matrix (i.e., H(A) approximately 2H(A)(eff)/3). A strong dependence of this intrinsic modulus on salt concentration was found; therefore, it appears that proteoglycans contribute structurally to the magnitude of H(A), in a manner independent of osmotic pressure.

Animals↗

PubMed2005

Anisotropy, inhomogeneity, and tension-compression nonlinearity of human glenohumeral cartilage in finite deformation.

The tensile and compressive properties of human glenohumeral cartilage were determined by testing 120 rectangular strips in uniaxial tension and 70 cylindrical plugs in confined compression, obtained from five human glenohumeral joints. Specimens were harvested from five regions across the articular surface of the humeral head and two regions on the glenoid. Tensile strips were obtained along two orientations, parallel and perpendicular to the split-line directions. Two serial slices through the thickness, corresponding to the superficial and middle zones of the cartilage layers, were prepared from each tensile strip and each compressive plug. The equilibrium tensile modulus and compressive aggregate modulus of cartilage were determined from the uniaxial tensile and confined compression tests, respectively. Significant differences in the tensile moduli were found with depth and orientation relative to the local split-line direction. Articular cartilage of the humeral head was significantly stiffer in tension than that of the glenoid. There were significant differences in the aggregate compressive moduli of articular cartilage between superficial and middle zones in the humeral head. Furthermore, tensile and compressive stress-strain responses exhibited nonlinearity under finite strain, while the tensile modulus differed by up to two orders of magnitude from the compressive aggregate modulus at 0% strain, demonstrating a high degree of tension-compression nonlinearity. The complexity of the mechanical properties of human glenohumeral cartilage was exposed in this study, showing anisotropy, inhomogeneity, and tension-compression nonlinearity within the same joint. The observed differences in the tensile properties of human glenohumeral cartilage suggest that the glenoid may be more susceptible to cartilage degeneration than the humeral head.

Aged↗

PubMed2005

Effects of enzymatic degradation on the frictional response of articular cartilage in stress relaxation.

It was recently shown experimentally that the friction coefficient of articular cartilage correlates with the interstitial fluid pressurization, supporting the hypothesis that interstitial water pressurization plays a fundamental role in the frictional response by supporting most of the load during the early time response. A recent study showed that enzymatic treatment with chondroitinase ABC causes a decrease in the maximum fluid load support of bovine articular cartilage in unconfined compression. The hypothesis of this study is that treatment with chondroitinase ABC will increase the friction coefficient of articular cartilage in stress relaxation. Articular cartilage samples (n = 34) harvested from the femoral condyles of five bovine knee joints (1-3 months old) were tested in unconfined compression with simultaneous continuous sliding (+/-1.5 mm at 1 mm/s) under stress relaxation. Results showed a significantly higher minimum friction coefficient in specimens treated with 0.1 micro/ml of chondroitinase ABC for 24 h (micro(min) = 0.082+/-0.024) compared to control specimens (micro(min) = 0.047+/-0.014). Treated samples also exhibited higher equilibrium friction coefficient (micro(eq) = 0.232+/-0.049) than control samples (micro(eq) = 0.184+/-0.036), which suggest that the frictional response is greatly influenced by the degree of tissue degradation. The fluid load support was predicted from theory, and the maximum value (as a percentage of the total applied load) was lower in treated specimens (77+/-12%) than in control specimens (85+/-6%). Based on earlier findings, the increase in the ratio micro(min)/micro(eq) may be attributed to the decrease in fluid load support.

Animals↗

PubMed2005

Effect of dynamic loading on the frictional response of bovine articular cartilage.

The objective of this study was to test the hypotheses that (1) the steady-state friction coefficient of articular cartilage is significantly smaller under cyclical compressive loading than the equilibrium friction coefficient under static loading, and decreases as a function of loading frequency; (2) the steady-state cartilage interstitial fluid load support remains significantly greater than zero under cyclical compressive loading and increases as a function of loading frequency. Unconfined compression tests with sliding of bovine shoulder cartilage against glass in saline were carried out on fresh cylindrical plugs (n=12), under three sinusoidal loading frequencies (0.05, 0.5 and 1 Hz) and under static loading; the time-dependent friction coefficient mu(eff) was measured. The interstitial fluid load support was also predicted theoretically. Under static loading mu(eff) increased from a minimum value (mu(min)=0.005+/-0.003) to an equilibrium value (mu(eq)=0.153+/-0.032). In cyclical compressive loading tests mu(eff) similarly rose from a minimum value (mu(min)=0.004+/-0.002, 0.003+/-0.001 and 0.003+/-0.001 at 0.05, 0.5 and 1 Hz) and reached a steady-state response oscillating between a lower-bound (mu(lb)=0.092+/-0.016, 0.083+/-0.019 and 0.084+/-0.020) and upper bound (mu(ub)=0.382+/-0.057, 0.358+/-0.059, and 0.298+/-0.061). For all frequencies it was found that mu(ub)>mu(eq) and mu(lb)<mu(eq)(p<0.05). Under cyclical compressive loading the interstitial fluid load support was found to oscillate above and below the static loading response, with suction occurring over a portion of the loading cycle at steady-state conditions. All theoretical predictions and most experimental results demonstrated little sensitivity to loading frequency. On the basis of these results, both hypotheses were rejected. Cyclical compressive loading is not found to promote lower frictional coefficients or higher interstitial fluid load support than static loading.

Adaptation, Physiological↗

PubMed2005

A layered agarose approach to fabricate depth-dependent inhomogeneity in chondrocyte-seeded constructs.

Inspired by the depth-dependent inhomogeneity of articular cartilage, it was hypothesized that a novel layered agarose technique, using a 2% (wt/vol) top and a 3% (wt/vol) bottom layer, would create an inhomogenous tissue construct with distinct material properties in conjoined regions. The biochemical and mechanical development of these constructs was observed alongside uniform 2% and 3% constructs. Initially, uniform 3% agarose disks had the highest bulk Young's modulus (E(Y) approximately 28 kPa) of all groups. After 28 days of culture in 20% FBS-containing media, however, uniform 2% chondrocyte-seeded constructs achieved the highest Young's modulus compared to bilayered and 3% agarose disks. Though all three groups contained similar GAG content ( approximately 1.5% ww), uniform 2% agarose disks on day 28 possessed the highest collagen content ( approximately 1% ww). Unlike in either homogeneous construct type, microscopic analysis of axial strain fields in bilayered constructs in response to applied static compression revealed two mechanically disparate regions on day 0: a softer 2% layer and a stiffer 3% layer. With time in culture, this inhomogeneity became less distinct, as indicated by increased continuity in both the local displacement field and local E(Y), and depended on the level of FBS supplementation of the feed media, with lower FBS concentrations (10%) more closely maintaining the original distinction of material properties. These results shed positive light on a layered agarose technique for the production of inhomogeneous bilayered chondrocyte-seeded agarose constructs with applications for investigations of chondrocyte mechanotransduction and for possible use in the tissue engineering of inhomogeneous articular cartilage constructs.

Animals↗

PubMed2005

Patellofemoral joint biomechanics and tissue engineering.

Recent advances in the study of patellofemoral joint biomechanics have provided promising diagnosis and treatment modalities for patellofemoral joint disorders, such as quantitative assessment of cartilage lesions from noninvasive imaging, computer simulations of surgical procedures for optimizing surgical parameters and potentially predicting outcomes, and cartilage tissue engineering for the treatment of advanced degenerative joint disease. These technologies are still in development and their clinical potentials remain an ongoing topic of investigation. We review some of our progress in addressing these issues, and the important role of cartilage mechanics and lubrication in understanding the challenges regarding patellofemoral surgery and cartilage tissue engineering.

Biomechanical Phenomena↗

PubMed2004

Anisotropic strain-dependent material properties of bovine articular cartilage in the transitional range from tension to compression.

Articular cartilage exhibits complex mechanical properties such as anisotropy, inhomogeneity and tension-compression nonlinearity. This study proposes and demonstrates that the application of compressive loading in the presence of osmotic swelling can be used to acquire a spectrum of incremental cartilage moduli (EYi) and Poisson's ratios (upsilon ij) from tension to compression. Furthermore, the anisotropy of the tissue can be characterized in both tension and compression by conducting these experiments along three mutually perpendicular loading directions: parallel to split-line (1-direction), perpendicular to split-line (2-direction) and along the depth direction (3-direction, perpendicular to articular surface), accounting for tissue inhomogeneity between the surface and deep layers in the latter direction. Tensile moduli were found to be strain-dependent while compressive moduli were nearly constant. The peak tensile (+) Young's moduli in 0.15M NaCl were E+Y1=3.1+/-2.3, E+Y2=1.3+/-0.3, E+Y3(Surface)=0.65+/-0.29 and E+Y3(Deep)=2.1+/-1.2 MPa. The corresponding compressive (-) Young's moduli were E-Y1=0.23+/-0.07, E-Y2=0.22+/-0.07, E-Y3(Surface)=0.18+/-0.07 and E-Y3(Deep)=0.35+/-0.11 MPa. Peak tensile Poisson's ratios were upsilon+12=0.22+/-0.06, upsilon+21=0.13+/-0.07, upsilon+31(Surface)=0.10+/-0.03 and upsilon+31(Deep)=0.20+/-0.05 while compressive Poisson's ratios were upsilon-12=0.027+/-0.012, upsilon-21=0.017+/-0.07, upsilon-31(Surface)=0.034+/-0.009 and upsilon-31(Deep)=0.065+/-0.024. Similar measurements were also performed at 0.015 M and 2 M NaCl, showing strong variations with ionic strength. Results indicate that (a) a smooth transition occurs in the stress-strain and modulus-strain responses between the tensile and compressive regimes, and (b) cartilage exhibits orthotropic symmetry within the framework of tension-compression nonlinearity. The strain-softening behavior of cartilage (the initial decrease in EYi with increasing compressive strain) can be interpreted in the context of osmotic swelling and tension-compression nonlinearity.

Animals↗

PubMed2004

Microscale frictional response of bovine articular cartilage from atomic force microscopy.

The objective of this study was to compare micro- and macroscale friction coefficients of bovine articular cartilage. Microscale measurements were performed using standard atomic force microscopy (AFM) techniques, using a 5 microm spherical probe tip. Twenty-four cylindrical osteochondral plugs were harvested in pairs from adjacent positions in six fresh bovine humeral heads (4-6 months old), and divided into two groups for AFM and macroscopic friction measurements. AFM measurements of friction were observed to be time-independent, whereas macroscale measurements demonstrated the well-documented time-dependent increase from a minimum to an equilibrium value. The microscale AFM friction coefficient (mu(AFM), 0.152+/-0.079) and macroscale equilibrium friction coefficient (mu(eq), 0.138+/-0.036) exhibited no statistical differences (p=0.50), while the macroscale minimum friction coefficient (mu(min), 0.004+/-0.001) was significantly smaller than mu(eq) and mu(AFM) (p<0.0001). Variations in articular surface roughness (Rq= 462+/-216 nm) did not correlate significantly with mu(AFM), mu(eq) or mu(min). The effective compressive modulus determined from AFM indentation tests using a Hertz contact analysis was E*=45.8+/-18.8 kPa. The main finding of this study is that mu(AFM) is more representative of the macroscale equilibrium friction coefficient, which represents the frictional response in the absence of cartilage interstitial fluid pressurization. These results suggest that AFM measurements may be highly suited for exploring the role of boundary lubricants in diarthrodial joint lubrication independently of the confounding effect of fluid pressurization to provide greater insight into articular cartilage lubrication.

Animals↗

PubMed2004

Experimental verification of the role of interstitial fluid pressurization in cartilage lubrication.

The objective of the current study was to measure the friction coefficient simultaneously with the interstitial fluid load support in bovine articular cartilage, while sliding against glass under a constant load. Ten visually normal 6-mm-diameter cartilage plugs harvested from the humeral head of four bovine shoulder joints (ages 2-4 months) were tested in a custom friction device under reciprocating linear motion (range of translation +/-2 mm; sliding velocity 1 mm/s), subjected to a 4.5 N constant load. The frictional coefficient was found to increase with time from a minimum value of mu min=0.010+/-0.007 (mean+/-SD) to a maximum value of 0.243+/-0.044 over a duration ranging from 920 to 19,870 s (median: 4,560 s). The corresponding interstitial fluid load support decreased from a maximum of 88.8+/-3.8% to 8.7+/-8.6%. A linear correlation was observed between the frictional coefficient and interstitial fluid load support (r2=0.96+/-0.03). These results support the hypothesis that the temporal variation of the frictional coefficient correlates negatively with the interstitial fluid load support and that consequently interstitial fluid load support is a primary mechanism regulating the frictional response in articular cartilage. Fitting the experimental data to a previously proposed biphasic boundary lubrication model for cartilage yielded an equilibrium friction coefficient of mu eq=0.284+/-0.044. The fraction of the apparent contact area over which the solid cartilage matrix was in contact with the glass slide was predicted at phi s=1.7+/-6.3%, significantly smaller than the solid volume fraction of the tissue, phi s=13.8+/-1.8%. The model predictions suggest that mixed lubrication prevailed at the contact interface under the loading conditions employed in this study.

Animals↗

PubMed2004

The correspondence between equilibrium biphasic and triphasic material properties in mixture models of articular cartilage.

Mixture models have been successfully used to describe the response of articular cartilage to various loading conditions. Mow et al. (J. Biomech. Eng. 102 (1980) 73) formulated a biphasic mixture model of articular cartilage where the collagen-proteoglycan matrix is modeled as an intrinsically incompressible porous-permeable solid matrix, and the interstitial fluid is modeled as an incompressible fluid. Lai et al. (J. Biomech. Eng. 113 (1991) 245) proposed a triphasic model of articular cartilage as an extension of their biphasic theory, where negatively charged proteoglycans are modeled to be fixed to the solid matrix, and monovalent ions in the interstitial fluid are modeled as additional fluid phases. Since both models co-exist in the cartilage literature, it is useful to show how the measured properties of articular cartilage (the confined and unconfined compressive and tensile moduli, the compressive and tensile Poisson's ratios, and the shear modulus) relate to both theories. In this study, closed-form expressions are presented that relate biphasic and triphasic material properties in tension, compression and shear. These expressions are then compared to experimental findings in the literature to provide greater insight into the measured properties of articular cartilage as a function of bathing solutions salt concentrations and proteoglycan fixed-charge density.

Animals↗

PubMed2004

A paradigm for functional tissue engineering of articular cartilage via applied physiologic deformational loading.

Deformational loading represents a primary component of the chondrocyte physical environment in vivo. This review summarizes our experience with physiologic deformational loading of chondrocyte-seeded agarose hydrogels to promote development of cartilage constructs having mechanical properties matching that of the parent calf tissue, which has a Young's modulus E(Y) = 277 kPa and unconfined dynamic modulus at 1 Hz G* = 7 MPa. Over an 8-week culture period, cartilage-like properties have been achieved for 60 x 10(6) cells/ml seeding density agarose constructs, with E(Y) = 186 kPa, G* = 1.64 MPa. For these constructs, the GAG content reached 1.74% ww and collagen content 2.64% ww compared to 2.4% ww and 21.5% ww for the parent tissue, respectively. Issues regarding the deformational loading protocol, cell-seeding density, nutrient supply, growth factor addition, and construct mechanical characterization are discussed. In anticipation of cartilage repair studies, we also describe early efforts to engineer cylindrical and anatomically shaped bilayered constructs of agarose hydrogel and bone (i.e., osteochondral constructs). The presence of a bony substrate may facilitate integration upon implantation. These efforts will provide an underlying framework from which a functional tissue-engineering approach, as described by Butler and coworkers (2000), may be applied to general cell-scaffold systems adopted for cartilage tissue engineering.

Algorithms↗

PubMed2004

Cartilage interstitial fluid load support in unconfined compression following enzymatic digestion.

Interstitial fluid pressurization plays an important role in cartilage biomechanics and is believed to be a primary mechanism of load support in synovial joints. The objective of this study was to investigate the effects of enzymatic degradation on the interstitial fluid load support mechanism of articular cartilage in unconfined compression. Thirty-seven immature bovine cartilage plugs were tested in unconfined compression before and after enzymatic digestion. The peak fluid load support decreased significantly (p < 0.0001) from 84 +/- 10% to 53 +/- 19% and from 80 +/- 10% to 46 +/- 21% after 18-hours digestion with 1.0 u/mg-wet-weight and 0.7 u/mg-wet-weight of collagenase, respectively. Treatment with 0.1 u/ml of chondroitinase ABC for 24 hours also significantly reduced the peak fluid load support from 83 +/- 12% to 48 +/- 16% (p < 0.0001). The drop in interstitial fluid load support following enzymatic treatment is believed to result from a decrease in the ratio of tensile to compressive moduli of the solid matrix.

Animals↗

PubMed2004

Role of cell-associated matrix in the development of free-swelling and dynamically loaded chondrocyte-seeded agarose gels.

Chondrocytes embedded in agarose and subjected to dynamic deformational loading produce a functional matrix with time in culture, but there is usually a delay in the development of significant differences compared to free swelling. In this study, we hypothesized that the initial presence of a cell-associated matrix would expedite construct development in response to dynamic deformational loading. Seeded samples with enzymatically isolated chondrocytes and chondrons (the chondrocyte and its pericellular matrix) and examined the effects of seeding density and dynamic loading on the development of tissue properties. At 60 million/ml, dynamic loading significantly augmented the development of material properties in chondrocyte- and chondron-seeded constructs. Biochemical content and histological analysis indicated that the deposition of GAG, link protein and collagens are affected by the pre-existing cell-associated matrix of the chondron-seeded samples. The pericellular matrix associated with the chondrons did not expedite the development of material properties in response to deformational loading, disproving our hypothesis. The relative concentration and distribution of matrix proteins may play a major role in the disparate responses observed for the chondrocyte- and chondron-seeded cultures. In further support of these findings, culturing chondrocytes in agarose for two weeks prior to the application of deformational loading also did not exhibit expedited construct development.

Adaptation, Physiological↗