Thesis (M.S.)--School of Mechanical Engineering, Georgia Institute of Technology, 2005. Directed by Marc Levenston. / Marc Levenston, Committee Co-Chair ; Yves Berthelot, Committee Co-Chair ; Robert Guldberg, Committee Member. Includes bibliographical references.

Thesis (Ph. D.)--Mechanical Engineering, Georgia Institute of Technology, 2007. / Radhakrishna, Harish, Committee Member ; LaPlaca, Michelle, Committee Member ; Nerem, Robert, Committee Member ; Garcia, Andres, Committee Member ; Levenston, Marc, Committee Chair.

Objective: Physical exercise decreases disability and pain associated with chronic articular cartilage degradation. However, understanding of the pathology is lacking. In this study, the levels of 17 biomarkers of inflammation and cartilage degradation were measured in synovial fluid (SF) before and after a 30-minute run in able-bodied and previously-injured individuals. Materials & Methods: Four able-bodied recreational runners (3 men and 1 woman: 24 ± 2 years, 68 ± 7 kg, and 173 ± 9 cm) and 4 recreational runners who had undergone a unilateral anterior cruciate ligament reconstruction (ACLr) (2 men and 2 women: 23 ± 1 years, 71 ± 6 kg, and 175 ± 4 cm) were recruited to participate in this study. Using a saline-assisted method, SF was aspirated before and after both a 30-minute unloading and 30-minute exercise session. Samples were corrected for blood contamination and analyzed for 15 cytokines and 2 matrix metalloproteinases (MMPs). Mixed model analyses were used to determine the main effects of session, case/control status, pre/post aspirations, and the interactions between case/control status and pre/post aspirations. Results: Blood protein contamination was calculated and accounted for in 15 of 32 synovial fluid samples. Granulocyte colony stimulating factor (GCSF) was the only detectable cytokine of the 15 analyzed. No statistical differences were found in GCSF concentrations between pretreatment and posttreatment aspirations (p = 0.45), ACLr and able-bodied control groups (p = 0.60), or unloading and exercise sessions (p = 0.96). MMP-13 was undetectable. No statistical differences were found in MMP-3 between pretreatment and posttreatment aspirations (p = 0.15), ACLr and able-bodied control groups (p = 0.85), or unloading and exercise sessions (p = 0.14).Conclusions: Two (GCSF and MMP-3) of the 17 measured biomarkers were detectable. There were no significant differences in either GCSF or MMP-3 due to a 30-minute run or 30-minute unloading period in either the able-bodied or ACLr participants. Further, there were no significant differences between biomarker concentrations and case-control status. A novel method of controlling for blood contamination in synovial fluid samples was implemented.

Osteoarthritis is a progressive degenerative disease which affects the cartilage in articulating joints. The progression of osteoarthritis is known to be mechanically mediated, though specific mechanical factors have yet to be identified. In particular, the effects of frictional interactions and altered mechanical homeostasis remain unknown, and the inability to link specific mechanisms to disease advancement hinders the development of treatment strategies. The overarching objective of this dissertation is to study the mechanically-mediated fatigue failure process in articular cartilage through a validated computational model to ascertain the relative importance of mechanical factors, including surface friction and bulk cyclic stresses, on progression of osteoarthritis. Fatigue failure in cartilage progresses as a function of multiple mechanical and physicochemical interactions. Collagen fibrils are the primary constituents that fail under fatigue loading. As the collagen fails, homeostasis between osmotic pressure and collagen tension is disrupted and the cartilage imbibes water and swells, producing softening. This entire process occurs under frictional contact loading. From a modeling standpoint, several primary challenges arise: (1) Accounting for the osmotic swelling of cartilage, which has not been sufficiently characterized experimentally; (2) Developing finite element algorithms to handle frictional contact of charged multiphasic (solid-fluid-solute) materials such as cartilage; (3) Modeling fatigue mechanics with observable state variables representing measures of cartilage composition, such that imaging techniques may inform the theory; and (4) Formulating compatible plasticity theories to allow validation of the novel fatigue framework with the extensive literature on fatigue of metals. This dissertation addressed these challenges in pursuit of the overarching objective. Direct experimental measurements revealed the osmotic swelling pressure in cartilage does not obey ideal Donnan law, which significantly overestimates the measured pressure by approximately a factor of three. The aggregate modulus in triphasic theory was found to vary strongly with the external concentration, increasing three- to five-fold between hypertonic and hypotonic solutions. These results allow us to capture the interaction of swelling with damage. The fatigue process is coupled with swelling, and computer modeling must be performed in a multiphasic environment which accounts for flow of charged ions. To address this, a novel surface-to-surface finite element algorithm for frictional contact was developed, providing the capabilities of complex surface-smoothing algorithms while retaining the simplicity of node-to-segment methods. This powerful framework was adapted to model friction between porous-permeable tissues, resulting in the development, implementation, and validation of finite element algorithms for four different types (single-phase elastic, biphasic, biphasic-solute, and multiphasic) of frictional contact. For the latter three, our work represented the first algorithms of this type. These algorithms are applied to model cartilage friction. By using constrained reactive mixture theory, we developed a reactive plasticity framework that reduced to classical Prandtl-Reuss plasticity theory in the limit of infinitesimal deformation, using only scalar state variables representing composition measures. Applying this reaction kinetics-based approach to model fatigue mechanics provided a valid theoretical framework for treating evolving damage, where measures of the mass composition of cartilage served as observable state variables. By incorporating reactive plasticity, our reactive fatigue theory was thoroughly validated against experimental data from metals and biological tissues, including human tendon and human cartilage. These modeling efforts were then synthesized to develop a fully validated computational model of fatigue failure in articular cartilage. For the first time, the role of frictional interactions on the progression of fatigue in articular cartilage was quantified. Results demonstrate that friction has an effect, but it is relatively small compared to the magnitude of the damage which takes place due to contact loads raising the magnitude of stresses in the collagen matrix. The implication of this result is that fatigue accumulation in cartilage is more sensitive to contact loading rather than surface interactions such as friction. This key finding may have clinical implications regarding treatment strategies for early-stage osteoarthritis. This dissertation has generated a novel suite of theoretical and computational tools which have facilitated the development of a fully validated computational model of fatigue failure in articular cartilage. Replicating previous experimental fatigue studies with the model has confirmed that bulk matrix stresses are responsible for the majority of fatigue-induced damage, and that friction plays a relatively minor role. Future work will apply these computational models to further analyze fatigue failure in fibrous biological tissues and study experimentally-generated hypotheses.

京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第21672号 / 医博第4478号 / 新制||医||1035(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 川上 浩司, 教授 古川 壽亮, 教授 上杉 志成 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

This paper presents a biotribological study on cartilage wear and friction, using a system of cartilage-on-stainless steel. This study is a part of the ongoing biotribology research by Dr. Furey at the Virginia Polytechnic Institute and State University. Two loads (65 N and 20 N) and three lubricants (saline reference, reference + hyaluronic acid, and bovine synovial fluid) were tested and evaluated using several analysis techniques. These techniques included wear analysis by hydroxyproline measurement, scanning electron microscopy (SEM), histologic sectioning and staining, numerical analysis of friction and specimen displacement data, and Fourier transform infrared (FTIR) analysis. Biochemical wear analysis showed that, under high load, the saline reference generated the most wear, hyaluronic acid produced less wear, and bovine synovial fluid produced the least. Wear was sensitive to load with all three lubricants, but was not significantly affected by the lubricant under low load. SEM photographs and histologic sections showed evidence of plowing and surface delamination, as well as another wear mechanism that produced wear markings perpendicular to the direction of sliding. Opaque films remained on the polished stainless steel disks after saline and hyaluronic acid tests, but not after synovial fluid tests. FTIR analysis of these films, as well as fresh and worn cartilage, showed that the cartilage experienced chemical changes during sliding. / Master of Science

During ambulation, lower-extremity joint angles and net moments influence knee joint load. It is unclear which mechanical variables most strongly correlate with acute articular cartilage (AC) catabolism in response to ambulation. Purpose: To determine which mechanical variables are most strongly correlated to acute AC catabolism, and to test the acute effect of ambulation speed on AC catabolism, while controlling for load frequency. Methods: 18 able-bodied subjects (9 male, 9 female; age = 23 ± 2 y; mass = 68.3 ± 9.6 kg; height = 1.70 ± 0.08 m) completed three separate ambulation sessions: slow (preferred walking speed), medium (+50% of walking speed), and fast (+100% of walking speed). For each session, subjects completed 4000 steps on an instrumented treadmill while ten high-speed cameras recorded synchronized video data. Various, discrete, three-dimensional joint kinematic and kinetic variables were averaged across 20 total stance phases (5 stance phases at 1000, 2000, 3000, and 4000 steps). Blood samples were collected pre-, post-, 30-min post-, and 60-min post-ambulation. Serum cartilage oligomeric matrix protein (COMP) concentration was determined using an enzyme-linked immunosorbent assay. A stepwise multiple linear regression analysis was used to evaluate the relationships between serum COMP change and lower-extremity joint angles and moments. A mixed model ANCOVA was used to evaluate serum COMP concentration between sessions across time. Results: Peak ankle inversion, knee extension, knee abduction, hip flexion, hip extension, and hip abduction moment, and knee flexion angle at impact, explained 61.4% of the total variance in serum COMP change (p < 0.001), due to ambulation. COMP concentration increased 28%, 18%, and 5% immediately after ambulation for the running, jogging, and walking sessions, respectively. All sessions were significantly different immediately post-ambulation (p < 0.01). Conclusion: Certain lower-extremity joint mechanics are associated with acute AC catabolism, due to ambulation. Several key mechanical variables (e.g., peak knee extension, knee abduction, and hip abduction moments) explain much regarding the variance in serum COMP increase. These lower-extremity variables can be used to predict acute AC catabolism, allowing researchers and clinicians to better predict and/or understand AC catabolism. Additionally, when load frequency is controlled, increased ambulation speed acutely results in increased AC catabolism. Ambulation speed does not, however, influence serum COMP elevation duration. Joint mechanics and load frequency appear to be responsible for the magnitude of COMP increase, while duration of COMP elevation post-ambulation is dictated by load frequency.

Poly(2-hydroxyethyl) methacrylate, (polyHEMA), hydrogels are synthesized for tribological study to investigate their potential for use as synthetic articular cartilage. A four factor, two level designed experiment was performed to evaluate friction and wear of polyHEMA. Tests were carried out using a friction and wear test device developed for biotribology research. The geometry consisted of a ball on flat; 6mm stainless steel ball and flat polyHEMA discs. Test factors were load, lubrication, hydration and material crosslink density. Linear oscillating sliding contact tests were performed on each polyHEMA disc for approximately 30 minutes per test. Friction coefficients found ranged from 0.05 to 1.7. Linear wear measured ranged from 0.02 mm to 1.32 mm. / Master of Science

Damage to articular cartilage, whether through degeneration (i.e. osteoarthritis) or acute injury, is particularly debilitating due to the tissue's limited regenerative capacity. These impairments are common: nearly 27 million Americans suffer from osteoarthritis and 36% of athletes suffer from traumatic cartilage defects. Allografts are the preferred treatment for large cartilage defects, but demand for these tissues outweighs their supply. To generate additional replacement tissues, tissue engineering strategies have been studied as a cell-based alternative therapy. Our laboratory has had great success repeatedly achieving native or near-native mechanical and biochemical properties in grafts engineered from chondrocyte-seeded agarose hydrogels. The most common iteration of this technique yields a disk of ~4 mm diameter and ~2.3 mm thickness. However, much work is still needed to increase the potential for clinical translation of this product. Our laboratory operates under the premise that in vivo success is predicated on replicating native graft properties in vitro. Compared to these engineered grafts, native grafts are larger in size. They consist of cartilage, which has properties varying in a depth-specific manner, anchored to a porous subchondral bone base. They are able to be stored between harvest and transplantation. This dissertation presents strategies to address a subset of the remaining challenges of reproducing these aspects in engineered grafts. First, graft macrostructure was addressed by incorporating a porous base to generate biomimetic osteochondral grafts. Previous studies have shown advantages to using porous metals as the bony base. Likewise, we confirmed that osteochondral constructs can be cultured to robust tissue properties using porous titanium bases. The titanium manufacturing method, selective laser melting, offers precise control, allowing for tailoring of base shape and pore geometry for optimal cartilage growth and osteointegration. In addition to viability studies, we investigated the influence of the porous base on the measured mechanical properties of the construct's gel region. Through measurements and correlation analysis, we linked a decrease in measured mechanical properties to pore area. We promote characterization of such parameters as an important consideration for the generation of functional grafts using any porous base. Next, we investigated a high intensity focused ultrasound (HIFU) denaturation of gel-incorporated albumin as a strategy for inducing local tissue property changes in constructs during in vitro growth. HIFU is a low cost, non-contact, non-invasive ultrasound modality that is used clinically and in the laboratory for such applications as ablation of uterine fibroids and soft tissue tumors. Denaturing such proteins has been shown to increase local stiffness. We displayed the ability incorporate albumin into tissue engineering relevant hydrogels, alter transport properties, and visualize treatment with its denaturation. HIFU treatment is aided by the porous metal base, allowing for augmented heating. Though heating cartilage is used in the clinic, it is associated with cell death. We investigated this effect, finding that the associated loss of viability remains localized to the treatment zone over time. This promotes the option of balancing desired changes in tissue properties against the concomitant cell viability loss. In order to match clinically utilized allografts, engineered constructs must be scaled up in size. This process is limited by diffusional transport of nutrients and other chemical factors, leading to preferential extracellular matrix deposition in the construct periphery. Many methods are being investigated for overcoming this limitation in fixed-size constructs. In this chapter, we investigated a novel strategy in which small constructs are cultured for future assembly. This modular assembly offers coverage of variable sized defects with more consistent growth with more uniform distribution of biochemical constituents than large constructs cultured on their own. Physiologic failure testing showed that integration of these tissues may be strengthened by increased subunit strength or assembled culture. It is expected that bioadhesive caulking and/or the incorporation of osteochondral bases would further increase integration of the assembled large graft. Finally, we sought to provide a preservation/storage protocol for engineered cartilage constructs. Such a technique is critical for clinical translation, providing the engineered graft with a “shelf-life.” We adopted and evaluated the Missouri Osteochondral Allograft Preservation System (MOPS), which had been shown to maintain cell viability in native grafts for at least 63 days at room temperature without serum or growth factors. Within the current clinical of 28 days, MOPS maintained chondrocyte viability and 75% of the pre-preservation Young's modulus without significant decline in biochemical content, however it did not extend the clinical window as it had with native grafts. Refrigeration with MOPS did not show any benefit at day 28, but proved better with longer preservation times. These results are the first evaluating engineered cartilage storage. Further optimization is necessary to extend storage tissue property maintenance in storage. Overall, this dissertation presents four strategies for increasing the translation potential of engineered articular cartilage grafts by better matching the clinically utilized native allograft system. Combining these techniques, one could ideally engineer small, interlocking ostechondral constructs with HIFU modified interface properties, which could be stored from maturity to implantation. Future optimization is required to better understand and utilize these methods to engineer fully functional, clinically relevant grafts.

Thesis (M.S.)--University of Missouri--Columbia, 2003. / "December 2003." Typescript. Vita. Includes bibliographical references (leaves 84-96). Also issued on the Internet.