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Solid-interstitial fluid interaction, which depends on tissue permeability, is significant to the strain-rate-dependent mechanical behavior of humeral head (shoulder) cartilage. Due to anatomical and biomechanical similarities to that of the human shoulder, kangaroos present a suitable animal model. Therefore, indentation experiments were conducted on kangaroo shoulder cartilage tissues from low (10(-4)/s) to moderately high (10(-2)/s) strain-rates. A porohyperelastic model was developed based on the experimental characterization; and a permeability function that takes into account the effect of strain-rate on permeability (strain-rate-dependent permeability) was introduced into the model to investigate the effect of rate-dependent fluid flow on tissue response. The prediction of the model with the strain-rate-dependent permeability was compared with those of the models using constant permeability and strain-dependent permeability. Compared to the model with constant permeability, the models with strain-dependent and strain-rate-dependent permeability were able to better capture the experimental variation at all strain-rates (p < 0.05). Significant differences were not identified between models with strain-dependent and strain-rate-dependent permeability at strain-rate of 5 × 10(-3)/s (p = 0.179). However, at strain-rate of 10(-2)/s, the model with strain-rate-dependent permeability was significantly better at capturing the experimental results (p < 0.005). The findings thus revealed the significance of rate-dependent fluid flow on tissue behavior at large strain-rates, which provides insights into the mechanical deformation mechanisms of cartilage tissues., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Background: Semipermeability to fluid transport is one of the principal attributes of a tissue like articular cartilage. Consequently, this characteristic can be exploited in attempts to understand the functional roles of the biological layer of Surface Active Phospholipids (SAPL) which form on its surfaces. A previous study, relevant to peritoneal SAPL was carried out in which hypertonic glucose solution was dialysed against physiological saline through SAPL membrane and concluded that SAPL possessed semipermeability. Our analysis extends this previous study by dialysing hypertonic and hypotonic saline solutions against physiological saline via SAPL membranes which is more relevant to the articular joint environment., Material/methods: Membranes were produced from either synthetic or bovine cartilage SAPL and used to carry out tests involving the dialysis of hypotonic and hypertonic sodium chloride solutions against physiological saline, using an Ussing chamber to hold both the membranes and dialysis fluids., Results: The dialysis produced osmotic pressures which are commensurate with our experimental constraints, but strongly indicated that it is indeed possible to generate osmotic pressures using SAPL membranes, indicating the semipermeability of this lipid structure., Conclusions: It is widely accepted that the collagen-proteoglycan membrane provides the semipermeability of articular cartilage despite the low levels of osmotic pressure recorded in our experiments, our results demonstrate that SAPL aggregation can constitute a semipermeable layer with a strong capability to contribute to the semipermeablity of the collagen-proteoglycan system especially on the surface of the tissue. Consequently its deficiency, as seen in osteoarthritis could lead/contribute to cartilage dysfunction.

Due to anatomical and biomechanical similarities to human shoulder, kangaroo was chosen as a model to study shoulder cartilage. Comprehensive enzymatic degradation and indentation tests were applied on kangaroo shoulder cartilage to study mechanisms underlying its strain-rate-dependent mechanical behavior. We report that superficial collagen plays a more significant role than proteoglycans in facilitating strain-rate-dependent behavior of the kangaroo shoulder cartilage. By comparing the mechanical properties of degraded and normal cartilages, it was noted that proteoglycan and collagen degradation significantly compromised strain-rate-dependent mechanical behavior of the cartilage. Superficial collagen contributed equally to the tissue behavior at all strain-rates. This is different to the studies reported on knee cartilage and confirms the importance of superficial collagen on shoulder cartilage mechanical behavior. A porohyperelastic numerical model also indicated that collagen disruption would lead to faster damage of the shoulder cartilage than when proteoglycans are depleted. [ABSTRACT FROM AUTHOR]

This paper investigates the potential of pulsed power to sterilize hard and soft tissues and its impact on their physico-mechanical properties. It hypothesizes that pulsed plasma can sterilize both vascular and avascular tissues and the transitive layers in between without deleterious effects on their functional characteristics. Cartilage/bone laminate was chosen as a model to demonstrate the concept, treated at low temperature, at atmospheric pressure, in short durations and in buffered environment using a purposed-built pulsed power unit. Input voltage and time of exposure were assigned as controlling parameters in a full factorial design of experiment to determine physical and mechanical alteration pre- and post-treatment. The results demonstrated that, discharges of 11 kV sterilized samples in 45 s, reducing intrinsic elastic modules from 1.4 ± 0.9 to 0.9 ± 0.6 MPa. There was a decrease of 14.1 % in stiffness and 27.8 % in elastic-strain energy for the top quartile. Mechanical impairment was directly proportional to input voltage ( P value < 0.05). Bacterial inactivation was proportional to treatment time for input voltages above 32 V ( P < 0.001; R = 0.98). Thermal analysis revealed that helix-coil transition decelerated with exposure time and collagen fibrils were destabilized as denaturation enthalpy reduced by 200 μV. We concluded by presenting a safe operating threshold for pulsed power plasma as a feasible protocol for effective sterilization of connective tissues with varying level of loss in mechanical robustness which we argue to be acceptable in certain medical and tissue engineering application. [ABSTRACT FROM AUTHOR]

A total histological grade does not necessarily distinguish between different manifestations of cartilage damage or degeneration. An accurate and reliable histological assessment method is required to separate normal and pathological tissue within a joint during treatment of degenerative joint conditions and to sub-classify the latter in meaningful ways. The Modified Mankin method may be adaptable for this purpose. We investigated how much detail may be lost by assigning one composite score/grade to represent different degenerative components of the osteoarthritic condition. We used four ovine injury models (sham surgery, anterior cruciate ligament/medial collateral ligament instability, simulated anatomic anterior cruciate ligament reconstruction and meniscal removal) to induce different degrees and potentially 'types' (mechanisms) of osteoarthritis. Articular cartilage was systematically harvested, prepared for histological examination and graded in a blinded fashion using a Modified Mankin grading method. Results showed that the possible permutations of cartilage damage were significant and far more varied than the current intended use that histological grading systems allow. Of 1352 cartilage specimens graded, 234 different manifestations of potential histological damage were observed across 23 potential individual grades of the Modified Mankin grading method. The results presented here show that current composite histological grading may contain additional information that could potentially discern different stages or mechanisms of cartilage damage and degeneration in a sheep model. This approach may be applicable to other grading systems. [ABSTRACT FROM AUTHOR]

This article outlines the motivation and preliminary investigations into a novel method of characterizing cartilage health for potential in vivo application. Current in vivo indentation techniques, which primarily rely on stiffness measurements based on axial data, are unable to adequately distinguish between healthy and degraded tissue. The present in vitro study investigates the effects of controlled artificial degradation on the effective surface stretch, comparing the results with those obtained from the peripheral cartilage surrounding focal osteoarthritis. Results suggest that this technique is highly sensitive, showing a maximum range of 14% effective surface stretch in a normal joint compared with 42% for axial strain measurements. We further demonstrated that the technique can discriminate between degenerative changes and the intrinsic variations in cartilage properties across the normal joint. From these investigations we propose that the relationship between indentation and the in-plane strain field under the indenter can better distinguish degraded tissue than the currently used stiffness techniques. [ABSTRACT FROM AUTHOR]

Background: Evidence has strongly indicated that surface-active phospholipid (SAPL), or surfactant, lines the surface of cartilage and serves as a lubricating agent. Previous clinical study showed that a saturated phosphatidylcholine (SPC), dipalmitoyl-phosphatidylcholine (DPPC), was effective in the treatment of osteoarthritis, however recent studies suggested that the dominant SAPL species at some sites outside the lung are not SPC, rather, are unsaturated phosphatidylcholine (USPC). Some of these USPC have been proven to be good boundary lubricants by our previous study, implicating their possible important physiological roles in joint if their existence can be confirmed. So far, no study has been conducted to identify the whole molecule species of different phosphatidylcholine (PC) classes on the surface of cartilage. In this study we identified the dominant PC molecule species on the surface of cartilage. We also confirmed that some of these PC species possess a property of semipermeability. Methods: HPLC was used to analyse the PC profile of bovine cartilage samples and comparisons of DPPC and USPC were carried out through semipermeability tests. Results: It was confirmed that USPC are the dominant SAPL species on the surface of cartilage. In particular, they are Dilinoleoyl-phosphatidylcholine (DLPC), Palmitoyl-linoleoylphosphatidylcholine, (PLPC), Palmitoyl-oleoyl-phosphatidylcholine (POPC) and Stearoyl-linoleoylphosphatidylcholine (SLPC). The relative content of DPPC (a SPC) was only 8%. Two USPC, PLPC and POPC, were capable of generating osmotic pressure that is equivalent to that by DPPC. Conclusion: The results from the current study confirm vigorously that USPC is the endogenous species inside the joint as against DPPC thereby confirming once again that USPC, and not SPC, characterizes the PC species distribution at non-lung sites of the body. USPC not only has better anti-friction and lubrication properties than DPPC, they also possess a level of semipermeability that is equivalent to DPPC. We therefore hypothesize that USPC can constitute a possible addition or alternative to the current commercially available viscosupplementation products for the prevention and treatment of osteoarthritis in the future. [ABSTRACT FROM AUTHOR]

Abstract: Background: Relative indentation characteristics are commonly used for distinguishing between normal healthy and degraded cartilage. The application of this parameter in surgical decision making and an appreciation of articular cartilage biomechanics has prompted us to hypothesise that it is difficult to define a reference stiffness to characterise normal articular cartilage. Methods: This hypothesis is tested for validity by carrying out biomechanical indentation of articular cartilage samples that are characterised as visually normal and degraded relative to proteoglycan depletion and collagen disruption. Compressive loading was applied at known strain rates to visually normal, artificially degraded and naturally osteoarthritic articular cartilage and observing the trends of their stress–strain and stiffness characteristics. Findings: While our results demonstrated a 25% depreciation in the stiffness of individual samples after proteoglycan depletion, they also showed that when compared to the stiffness of normal samples only 17% lie outside the range of the stress–strain behaviour of normal samples. Interpretation: We conclude that the extent of the variability in the properties of normal samples, and the degree of overlap (81%) of the biomechanical properties of normal and degraded matrices demonstrate that indentation data cannot form an accurate basis for distinguishing normal from abnormal articular cartilage samples with consequences for the application of this mechanical process in the clinical environment. [Copyright &y& Elsevier]