Mechanical effects of ionic replacements in articular cartilage. Part II: Simulations of successive substitutions of NaCl and CaCl(2).
A three-phase multi-species electro-chemo-mechanical model of articular cartilage was developed in a companion paper, Loret and Simões (in Biomech Model Mechanobiol, in press, DOI 10.1007/s10237-004-0062-7). The model can handle mechanical and chemical loadings and unloadings involving the two salts, NaCl and CaCl(2). In order to reproduce experimental data, the shielding effects are made cation-dependent. In a tensile experiment, at constant axial strain, refreshment of the bath in contact with the cartilage is observed, and simulated, to induce a much different increase in tension depending on the order of the chemical sequence to which the cartilage is exposed. For example, the sequence dw (distilled water)-NaCl-dw-CaCl(2)-dw results in a decrease in tension. But the initial tension is recovered if the chemical sequence is pursued by NaCl-dw. Therefore, ionic replacements are essentially reversible, as evidenced when the chemical loading events respect a certain symmetry. Distinct shielding effects by cations sodium and calcium stem from two main features: (1) different free enthalpies of formation that represent different affinities of the proteoglycans for these ions and that result in an equilibrium constant not equal to 1; (2) distinct valences but approximately the same diameter, which results in a more efficient shielding by cations calcium. The model accounts also: (1) for the anisotropy of the mechanical properties that are due to the strong orientation of collagen fibers; (2) for large deformations that occur during uniaxial traction with deionized water.
Loret
Benjamin
B
Laboratoire Sols, Solides, Structures, B.P. 53X, 38041, Grenoble Cedex, France. benjamin.loret@inpg.fr
Simões
Fernando M F
FM
D002122:Calcium Chloride / Q000737:chemistry*; D002138:Calibration; D002358:Cartilage, Articular / Q000737:chemistry* / Q000502:physiology*; D003094:Collagen / Q000737:chemistry; D006982:Hypertonic Solutions; D008954:Models, Biological; D012965:Sodium Chloride / Q000737:chemistry*; D013314:Stress, Mechanical; D014143:Traction; D016474:Weight-Bearing
D006982:Hypertonic Solutions; D012965:Sodium Chloride; D003094:Collagen; D002122:Calcium Chloride