Osteoarthritis is a debilitating joint disease characterized by the degradation of articular cartilage due to long term wear or acute injury. OA can lead to pain, limited mobility, and stiffness in the joint, and current treatment options often require invasive surgery or are limited to corrective attempts at mitigating pain. Due in part to the complexity of the disease and lack of holistic understanding of its advancement, there is no known treatment to halt or reverse the effects of OA progression in the joint. In order to address this need, the underlying mechanisms that drive the mechanical degradation of cartilage structure in its progression must be determined.
The objective of this dissertation is to (1) investigate the mechanical breakdown of cartilage through fatigue failure in physiologically relevant models and (2) to introduce a minimally invasive method for increasing the mechanical integrity of cartilage in an effort to reverse the effects of OA. In order to classify the mechanical mediation of wear in OA disease pathology, wear progression in human articular cartilage must be fully characterized. Human articular cartilage exhibits a remarkable resilience to wear during frictional sliding, making it difficult to induce damage in the tissue in experimental models. Previous work established reciprocal compressive stresses, and not frictional stresses, as the primary initiator of delamination fatigue wear in immature bovine cartilage.
In Chapter 2, we tested the hypothesis that reciprocal compressive stresses could induce fatigue wear in human articular cartilage and thus establish a reproducible and characterizable model of wear induction in human tissue. Human articular cartilage was subjected to 24 hours of frictional sliding in two contact configurations: stationary contact area (SCA), and migrating contact area (MCA). Five samples were tested in the SCA configuration, which induces frictional stresses, and five were tested in the MCA configuration, which induces reciprocal compressive stresses and frictional stresses. The SCA samples showed no conclusive damage after 24 hours of sliding, and recovered 99.3% ± 2.34% of their original thickness after testing. Three out of five MCA samples showed conclusive signs of damage, one in the form of tissue splitting, one in the form of blister formation, and one in the form of complete tissue tearing. The average friction coefficient in the SCA group (μ_SCA= 0.090 ± 0.008) was higher than the average friction coefficient in the MCA group (μ_MCA= 0.066±0.020; p=0.03). Although conducted as two separate studies, the results in Chapter 2 provide a preliminary data set to suggest that reciprocal compressive stresses are responsible for fatigue failure in human tissue, coherent with the results in the immature bovine model. Additionally, results of Chapter 2 establish a reproducible and physiologically relevant protocol for damage induction in human tissue. Future work will investigate this hypothesis with directly paired SCA and MCA human articular cartilage tissue samples of similar OA grade.
To further understand cartilage damage mechanics in physiologically relevant conditions, Chapter 3 and 4 investigate the role of synovial fluid in fatigue failure of immature bovine cartilage. Synovial fluid is often incorrectly identified as the source of low friction in cartilage sliding. In fact, it has an effect on the friction coefficient that is far secondary to interstitial fluid load support. Further, reciprocal compressive stresses, not frictional stresses, have been shown to be responsible for fatigue failure. It is imperative to understand the function of synovial fluid in wear mechanics. We tested the hypothesis that synovial fluid reduces the rate of fatigue failure in immature bovine articular cartilage due to the protective effects of its molecular constituents. Eight paired medial and lateral tibial plateaus were tested in MCA sliding in phosphate buffer saline (n=8) or synovial fluid (n=8) to directly compare fatigue rate in synovial fluid versus phosphate buffer saline. An additional study evaluated the effect of molecular constituents on wear rate by testing medial and lateral tibial plateaus in 50% (n=8) and 25% (n=8) synovial fluid diluted with phosphate buffer saline. All eight samples tested in phosphate buffer saline damaged after 24 hours of reciprocal sliding, and none of the samples tested in pure synovial fluid became damaged over the same duration. After an additional two days of sliding, two of eight samples tested in pure synovial fluid got damaged. In the samples tested in 50% and 25% synovial fluid-phosphate buffer saline dilutions, one sample and five samples got damaged after 72 hours of sliding respectively. The results of this study confirmed the hypothesis that synovial provides a protective effect against fatigue failure. The study also suggests that dilution of the synovial below a critical value reduces the concentration of molecular constituents available to protect the cartilage against damage.
Chapter 4 investigates the mechanism of synovial fluid’s protective effect further, by examining its potential to extend the duration of elevated fluid load support under compression and thereby reduce cartilage susceptibility to fatigue. The results of Chapter 4 illustrated that synovial fluid had no effect on the stress relaxation response of the cartilage to unconfined compression, disproving the presented hypothesis. Therefore, future work will investigate the function of synovial fluid in reducing the rate of fatigue, independent of its effect on friction.
The final two studies of this dissertation present a novel treatment modality to induce collagen crosslinks that enhance the cartilage equilibrium modulus. The technique introduced is presented as a minimally invasive alternative to current surgical interventions and proposes to increase the integrity of early-OA tissue. In Chapter 5, we investigate the hypothesis that low-level femtosecond laser treatment of cartilage can increase the stiffness of the equilibrium modulus without damaging tissue integrity or cell viability. In the first experiment, six immature bovine cartilage samples were treated with the laser and the equilibrium modulus was found to increase in stiffness (p<10⁻³). The technique was also applied to human articular cartilage tissue with “low” and “high” OA, and tissue was found to have an increase in equilibrium modulus (p=0.003 and p=0.03, respectively). Cell viability was preserved under these treatment conditions. Chapter 6 further outlines a safe envelope of laser treatment parameters through evaluation of the effect of thermal heating on the equilibrium modulus of cartilage samples. The results of this study found that temperatures above 65 ℃ (p<10⁻³) increase the tissue modulus, but no change in modulus occurs below 65 ℃ (p=1.00). The results of Chapter 6 provide an insight to the mechanical effect of thermal exposure, and informed the laser treatment parameters presented in Chapter 5, which were confirmed to produce thermal heating far below temperatures that result in thermal stiffening. Through the results presented in Chapter 5 and 6, preliminary data is provided to introduce a novel method for crosslink induction in the superficial zone of articular cartilage. In future work, this technique can be applied as a potential strategy to increase fatigue wear resistance, and to reduce the progression of OA in diseased tissue.
The work presented in this dissertation seeks to contribute to the understanding of fatigue wear in articular cartilage under physiologically relevant conditions, as well as introduce a method for enhancing cartilage tissue properties with laser treatment. In the first half of the dissertation, the effect of reciprocal compressive stresses was evaluated in human articular cartilage tissue and in immature bovine cartilage immersed in synovial fluid in an effort to understand the mechanism of delamination fatigue failure in OA progression. In the second half, a laser treatment modality was shown to increase tissue equilibrium modulus stiffness without compromising tissue viability.
| Identifer | oai:union.ndltd.org:columbia.edu/oai:academiccommons.columbia.edu:10.7916/btat-fy23 |
| Date | January 2024 |
| Creators | Sise, C.V. |
| Source Sets | Columbia University |
| Language | English |
| Detected Language | English |
| Type | Theses |
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