Direct Osmotic Pressure Measurements in Articular Cartilage Demonstrate Nonideal and Concentration-Dependent Phenomena

2020 ◽  
Vol 143 (4) ◽  
Author(s):  
Brandon K. Zimmerman ◽  
Robert J. Nims ◽  
Alex Chen ◽  
Clark T. Hung ◽  
Gerard A. Ateshian
Keyword(s):  
Articular Cartilage ◽  
Stress Relaxation ◽  
Osmotic Pressure ◽  
Electrostatic Interactions ◽  
Swelling Pressure ◽  
Confined Compression ◽  
Human Cartilage ◽  
Poisson Boltzmann ◽  
Triphasic Theory

Abstract The osmotic pressure in articular cartilage serves an important mechanical function in healthy tissue. Its magnitude is thought to play a role in advancing osteoarthritis. The aims of this study were to: (1) isolate and quantify the magnitude of cartilage swelling pressure in situ; and (2) identify the effect of salt concentration on material parameters. Confined compression stress-relaxation testing was performed on 18 immature bovine and six mature human cartilage samples in solutions of varying osmolarities. Direct measurements of osmotic pressure revealed nonideal and concentration-dependent osmotic behavior, with magnitudes approximately 1/3 those predicted by ideal Donnan law. A modified Donnan constitutive behavior was able to capture the aggregate behavior of all samples with a single adjustable parameter. Results of curve-fitting transient stress-relaxation data with triphasic theory in febio demonstrated concentration-dependent material properties. The aggregate modulus HA increased threefold as the external concentration decreased from hypertonic 2 M to hypotonic 0.001 M NaCl (bovine: HA=0.420±0.109 MPa to 1.266±0.438 MPa; human: HA=0.499±0.208 MPa to 1.597±0.455 MPa), within a triphasic theory inclusive of osmotic effects. This study provides a novel and simple analytical model for cartilage osmotic pressure which may be used in computational simulations, validated with direct in situ measurements. A key finding is the simultaneous existence of Donnan osmotic and Poisson–Boltzmann electrostatic interactions within cartilage.

An in Situ Dual Indentation and Optimization Method to Determine Mechanical Properties of Articular Cartilage

2007 ◽  
Author(s):  
Jonathan E. Pottle ◽  
J.-K. Francis Suh
Keyword(s):  
Articular Cartilage ◽  
Stress Relaxation ◽  
Structural Integrity ◽  
Reaction Force ◽  
Model Parameters ◽  
Unconfined Compression ◽  
Confined Compression ◽  
Practical Applications

The efficacy of the biphasic poroviscoelastic (BPVE) theory [1] in constitutive modeling of articular cartilage biomechanics is well-established [2–4]. Indeed, this model has been used to simultaneously predict stress relaxation force across confined compression, unconfined compression, and indentation protocols [2,3]. Previous works have also demonstrated success in simultaneously curve-fitting the BPVE model to reaction force and lateral deformation data gathered from stress relaxation tests of articular cartilage in unconfined compression [4]. However, a potential limitation of practical applications of such a successful model is seen in some commonly-employed mechanical testing methods for articular cartilage, such as confined compression and unconfined compression. These methods require the excision of a disk of cartilage from its underlying subchondral base, which likely would compromise the structural integrity of the tissue, causing swelling and curling artifacts of the sample [5]. Indentation represents a testing protocol that can be used with an intact cartilage layer. This results in a specimen more closely resembling cartilage in vivo. Using an agarose gel construct, our previous study [6] has demonstrated that a unique set of the six BPVE model parameters of a soft tissue can be determined readily from in situ dual indentation method using stress relaxation and creep viscoelastic protocols. The objective of the current study is to validate the efficacy of this technique as a means to determine the BPVE material parameters of articular cartilage.

INFLUENCE OF PRE-CONDITIONING LOADS ON BOVINE ARTICULAR CARTILAGE STRESS RELAXATION BEHAVIOR IN CONFINED COMPRESSION

2003 ◽  
Vol 07 (02) ◽  
pp. 145-150
Author(s):  
Diego Correa ◽  
Dennis Cullinane ◽  
Juan Carlos Briceño
Keyword(s):  
Mechanical Properties ◽  
Articular Cartilage ◽  
Stress Relaxation ◽  
Solid Phase ◽  
Test Chamber ◽  
Confined Compression ◽  
Equilibrium Stress ◽  
Bovine Articular Cartilage ◽  
Aggregate Modulus ◽  
Compression Chamber

Articular Cartilage is a load bearing tissue whose microarchitecture, electrochemical composition, and fluid interactions afford it unique mechanical properties. It consists of an extracellular matrix (ECM) interspersed with a sparse population of chondrocytes, varying in density by depth. The structure and mechanical properties of this highly specialized tissue also vary depending on depth from the articular surface; with three specialized zones, each with unique material properties. Typically this tissue is mechanically modeled as a biphasic material, consisting of a solid phase and a fluid phase, which can redistribute itself under loading, altering hydrostatic pressure within the material. Thus, articular cartilage exhibits a time-dependent viscoelastic behavior when subjected to constant loading or deformation, and will reach an equilibrium via stress relaxation and creep behavior. The objective of this study was to test a custom designed confined compression chamber. We characterize the ability of the test chamber to generate curves capable of quantifying the stress relaxation level and equilibrium state in bovine articular cartilage, and to show the preliminary results of a comparison between the equilibrium aggregate modulus (HA) obtained from pre- conditioned and non-conditioned tissues. Using fresh bovine articular cartilage samples, stress relaxation tests were conducted in compression, obtaining equilibrium stress and HA through a linear relation between the initial strain and the equilibrium stress. The test specimens were divided into two groups, one with a pre-conditioning load and the other without. The tests resulted in equilibrium stresses of 0.015 ± 0.0067 MPa for the non-conditioned and 0.067 ± 0.012 MPA for the pre-conditioned, and HA values of 0.205 ± 0.100 MPa for the unconditioned group and 0.878 ± 0.160 MPa in the pre-conditioned group. Our confined compression chamber successfully produced the stress relaxation curve characterizing the mechanical behavior of articular cartilage, defining both the equilibrium stress and HA. Our results suggest that pre-conditioning correlates with a higher equilibrium stress and aggregate modulus based on the fact that pre-loading the specimens reduces the effects of viscoelasticity.

A Triphasic Theory for the Swelling and Deformation Behaviors of Articular Cartilage

1991 ◽  
Vol 113 (3) ◽  
pp. 245-258 ◽  
Author(s):  
W. M. Lai ◽  
J. S. Hou ◽  
V. C. Mow
Keyword(s):  
Articular Cartilage ◽  
Charge Density ◽  
Fixed Charge ◽  
Solid Matrix ◽  
Confined Compression ◽  
Fixed Charge Density ◽  
Chemical Expansion ◽  
Chemical Potentials ◽  
Free Swelling ◽  
Triphasic Theory

Swelling of articular cartilage depends on its fixed charge density and distribution, the stiffness of its collagen-proteoglycan matrix, and the ion concentrations in the interstitium. A theory for a tertiary mixture has been developed, including the two fluid-solid phases (biphasic), and an ion phase, representing cation and anion of a single salt, to describe the deformation and stress fields for cartilage under chemical and/or mechanical loads. This triphasic theory combines the physico-chemical theory for ionic and polyionic (proteoglycan) solutions with the biphasic theory for cartilage. The present model assumes the fixed charge groups to remain unchanged, and that the counter-ions are the cations of a single salt of the bathing solution. The momentum equation for the neutral salt and for the intersitial water are expressed in terms of their chemical potentials whose gradients are the driving forces for their movements. These chemical potentials depend on fluid pressure p, salt concentration c, solid matrix dilatation e and fixed charge density cF. For a uni-uni valent salt such as NaCl, they are given by μi = μoi + (RT/Mi)ln[γ±2c (c + c F)] and μW = μow + [p − RTφ(2c + cF) + Bwe]/ρTw, where R, T, Mi, γ±, φ, ρTw and Bw are universal gas constant, absolute temperature, molecular weight, mean activity coefficient of salt, osmotic coefficient, true density of water, and a coupling material coefficient, respectively. For infinitesimal strains and material isotropy, the stress-strain relationship for the total mixture stress is σ = − pI − TcI + λs(trE)I + 2μsE, where E is the strain tensor and (λs,μs) are the Lame´ constants of the elastic solid matrix. The chemical-expansion stress (− Tc) derives from the charge-to-charge repulsive forces within the solid matrix. This theory can be applied to both equilibrium and non-equilibrium problems. For equilibrium free swelling problems, the theory yields the well known Donnan equilibrium ion distribution and osmotic pressure equations, along with an analytical expression for the “pre-stress” in the solid matrix. For the confined-compression swelling problem, it predicts that the applied compressive stress is shared by three load support mechanisms: 1) the Donnan osmotic pressure; 2) the chemical-expansion stress; and 3) the solid matrix elastic stress. Numerical calculations have been made, based on a set of equilibrium free-swelling and confined-compression data, to assess the relative contribution of each mechanism to load support. Our results show that all three mechanisms are important in determining the overall compressive stiffness of cartilage.

Removal of Sulfated Glycosaminoglycans Has a Differential Effect on Permeability of Bovine Articular Cartilage as Measured by Direct Permeation and Stress Relaxation

2009 ◽  
Author(s):  
Heath B. Henninger ◽  
Clayton J. Underwood ◽  
Gerard A. Ateshian ◽  
Jeffrey A. Weiss
Keyword(s):  
Articular Cartilage ◽  
Stress Relaxation ◽  
Soft Tissues ◽  
Water Movement ◽  
Experimental Treatment ◽  
Test Methods ◽  
Confined Compression ◽  
Interstitial Fluid Flow ◽  
Bovine Articular Cartilage ◽  
The Impact

Permeability is defined as the ability of a fluid to pass through a porous medium. The ease of water movement is a determinant of the interstitial fluid flow-dependent viscoelastic properties of hydrated soft tissues and also modulates transport of solutes. For articular cartilage, permeability has been quantified directly via permeation experiments and indirectly by analyzing the data from stress relaxation testing under confined compression. It is unclear whether these different methods result in consistent measurements. This further complicates quantification of the effect of an experimental treatment on permeability such as the removal of sulfated glycosaminoglycans (GAGs) [1, 2]. The objective of this study was to elucidate the impact of sulfated GAGs on the permeability of articular cartilage using direct permeation versus stress relaxation testing, and to assess any differences in permeability calculated from the two test methods.

scholarly journals Comparison of Compressive Stress-Relaxation Behavior in Osteoarthritic (ICRS Graded) Human Articular Cartilage

2017 ◽  
Author(s):  
Rajesh Kumar ◽  
David M. Pierce ◽  
Vidar Isaksen ◽  
Catharina de Lange Davies ◽  
Jon O. Drogset ◽  
...  
Keyword(s):  
Articular Cartilage ◽  
Stress Relaxation ◽  
Computational Models ◽  
Articular Surface ◽  
Significant Loss ◽  
Relaxation Behavior ◽  
Human Articular Cartilage ◽  
Osteoarthritic Cartilage ◽  
Human Cartilage ◽  
Stress Relaxation Behavior

Osteoarthritis (OA) is a common joint disorder found mostly in elderly people. The role of mechanical behavior in the progression of OA is complex and remains unclear. The stress-relaxation behavior of human articular cartilage in clinically defined osteoarthritic stages may have importance in diagnosis and prognosis of OA. In this study we investigated differences in the biomechanical responses among human cartilage of ICRS grades I, II and III using polymer dynamics theory. We collected 24 explants of human articular cartilage (eight each of ICRS grade I, II and III) and acquired stress-relaxation data applying a continuous load on the articular surface of each cartilage explant for 1180 s. We observed a significant decrease in Young’s modulus, stress-relaxation time, and stretching exponent in advanced stages of OA (ICRS grade III). The stretch exponential model indicated that significant loss in hyaluronic acid polymer might be the reason for the loss of proteoglycan in advanced OA. This work encourages further biomechanical modelling of osteoarthritic cartilage utilizing these data as input parameters to enhance the fidelity of computational models aimed at revealing how mechanical behaviors play a role in pathogenesis of OA.

A New Method for Determination of the Tensile Modulus of Articular Cartilage In Situ in a Free-Swelling Configuration

1999 ◽  
Author(s):  
Daria A. Narmoneva ◽  
Jean Y. Wang ◽  
Lori A. Setton
Keyword(s):  
Strain Tensor ◽  
Tensile Modulus ◽  
Small Animal ◽  
Swelling Pressure ◽  
Uniaxial Tensile ◽  
Collagen Network ◽  
Human Cartilage ◽  
Uniaxial Tensile Testing ◽  
Free Swelling

Abstract Studies of cartilage swelling have been used to demonstrate the effects of collagen network damage associated with osteoarthritis (OA) [1,7]. Elevated swelling, or increased hydration, is generally observed in fibrillated and degenerated cartilage where the integrity of the collagen network is insufficient to restrain the interstitial swelling pressure [8]. We recently developed an experimental method to quantify these swelling effects as components of a swelling-induced strain tensor in free-swelling tests of cartilage in situ [9]. Using this method, we were able to detect changes in swelling strains with cartilage degeneration in the meniscectomy model of OA [10]. In this study, we propose to quantify the material properties of canine and human cartilage studied in the free-swelling test and to compare them with site-matched values measured in uniaxial tensile testing. A triphasic constitutive model [6] was used to predict the components of strain in the free-swelling test for comparison with experimentally measured values. Values for the tensile modulus were found to compare well using the free-swelling and uniaxial testing methods. These findings demonstrate the potential of this new methodology for quantifying cartilage properties in small cartilage samples, such as in small animal models of OA.

In situ Time-Resolved Small-Angle X-ray Scattering Reveals the Formation Kinetics of Polyelectrolyte Complex Micelles

2019 ◽  
Author(s):  
Hao Wu ◽  
Jeffrey Ting ◽  
Siqi Meng ◽  
Matthew Tirrell
Keyword(s):  
Small Angle ◽  
Self Assembly ◽  
Electrostatic Interactions ◽  
Polyelectrolyte Complex ◽  
Time Resolved ◽  
X Ray ◽  
X Ray Scattering ◽  
Kinetics Of ◽  
Ray Scattering

We have directly observed the <i>in situ</i> self-assembly kinetics of polyelectrolyte complex (PEC) micelles by synchrotron time-resolved small-angle X-ray scattering, equipped with a stopped-flow device that provides millisecond temporal resolution. This work has elucidated one general kinetic pathway for the process of PEC micelle formation, which provides useful physical insights for increasing our fundamental understanding of complexation and self-assembly dynamics driven by electrostatic interactions that occur on ultrafast timescales.

scholarly journals Morphology Controlled Synthesis of γ-Al2O3 Nano-Crystallites in Al@Al2O3 Core–Shell Micro-Architectures by Interfacial Hydrothermal Reactions of Al Metal Substrates

Nanomaterials ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 310
Author(s):  
Dohyeon Han ◽  
Doohwan Lee
Keyword(s):  
Electrostatic Interactions ◽  
Heterogeneous Catalysts ◽  
Metal Substrate ◽  
Inorganic Anions ◽  
Core Shell ◽  
Hydroxyl Groups ◽  
Hydrothermal Reactions ◽  
Fine Control ◽  
Reaction Processes

Fine control of morphology and exposed crystal facets of porous γ-Al2O3 is of significant importance in many application areas such as functional nanomaterials and heterogeneous catalysts. Herein, a morphology controlled in situ synthesis of Al@Al2O3 core–shell architecture consisting of an Al metal core and a porous γ-Al2O3 shell is explored based on interfacial hydrothermal reactions of an Al metal substrate in aqueous solutions of inorganic anions. It was found that the morphology and structure of boehmite (γ-AlOOH) nano-crystallites grown at the Al-metal/solution interface exhibit significant dependence on temperature, type of inorganic anions (Cl−, NO3−, and SO42−), and acid–base environment of the synthesis solution. Different extents of the electrostatic interactions between the protonated hydroxyl groups on (010) and (001) facets of γ-AlOOH and the inorganic anions (Cl−, NO3−, SO42−) appear to result in the preferential growth of γ-AlOOH toward specific crystallographic directions due to the selective capping of the facets by adsorption of the anions. It is hypothesized that the unique Al@Al2O3 core–shell architecture with controlled morphology and exposed crystal-facets of the γ-Al2O3 shell can provide significant intrinsic catalytic properties with enhanced heat and mass transport to heterogeneous catalysts for applications in many thermochemical reaction processes. The direct fabrication of γ-Al2O3 nano-crystallites from Al metal substrate with in-situ modulation of their morphologies and structures into 1D, 2D, and 3D nano-architectures explored in this work is unique and can offer significant opportunities over the conventional methods.

scholarly journals Optical Biomarkers for the Diagnosis of Osteoarthritis through Raman Spectroscopy: Radiological and Biochemical Validation Using Ex Vivo Human Cartilage Samples

Diagnostics ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 546
Author(s):  
Paula Casal-Beiroa ◽  
Vanesa Balboa-Barreiro ◽  
Natividad Oreiro ◽  
Sonia Pértega-Díaz ◽  
Francisco J. Blanco ◽  
...  
Keyword(s):  
Raman Spectroscopy ◽  
Articular Cartilage ◽  
Ex Vivo ◽  
Cartilage Degradation ◽  
Calcium Pyrophosphate ◽  
Calcium Pyrophosphate Dihydrate ◽  
Label Free ◽  
Molecular Fingerprint ◽  
Human Cartilage ◽  
Biochemical Validation

Osteoarthritis (OA) is the most common rheumatic disease, characterized by progressive articular cartilage degradation. Raman spectroscopy (RS) has been recently proposed as a label-free tool to detect molecular changes in musculoskeletal tissues. We used cartilage samples derived from human femoral heads to perform an ex vivo study of different Raman signals and ratios, related to major and minor molecular components of articular cartilage, hereby proposed as candidate optical biomarkers for OA. Validation was performed against the radiological Kellgren–Lawrence (K-L) grading system, as a gold standard, and cross-validated against sulfated glycosaminoglycans (sGAGs) and total collagens (Hyp) biochemical contents. Our results showed a significant decrease in sGAGs (SGAGs, A1063 cm−1/A1004 cm−1) and proteoglycans (PGs, A1375 cm−1/A1004 cm−1) and a significant increase in collagen disorganization (ColD/F, A1245 cm−1/A1270 cm−1), with OA severity. These were correlated with sGAGs or Hyp contents, respectively. Moreover, the SGAGs/HA ratio (A1063 cm−1/A960 cm−1), representing a functional matrix, rich in proteoglycans, to a mineralized matrix-hydroxyapatite (HA), was significantly lower in OA cartilage (K-L I vs. III–IV, p < 0.05), whilst the mineralized to collagenous matrix ratio (HA/Col, A960 cm−1/A920 cm−1) increased, being correlated with K-L. OA samples showed signs of tissue mineralization, supported by the presence of calcium crystals-related signals, such as phosphate, carbonate, and calcium pyrophosphate dihydrate (MGP, A960 cm−1/A1004 cm−1, MGC, A1070 cm−1/A1004 cm−1 and A1050 cm−1/A1004 cm−1). Finally, we observed an increase in lipids ratio (IL, A1450 cm−1/A1670 cm−1) with OA severity. As a conclusion, we have described the molecular fingerprint of hip cartilage, validating a panel of optical biomarkers and the potential of RS as a complementary diagnostic tool for OA.

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