Previous decades of cartilage research have predominantly focused on decoupling the solid and fluid interactions of the mechanical response. The resulting biphasic and triphasic models are widely used in the biomechanics community. However, a simple viscoelastic model is able to account for the stress-relaxation behavior of cartilage, without the added complexity of solid and fluid interactions. Using a viscoelastic model, cartilage is considered a single material with elastic and dissipative properties. A mechanical characterization is made with fewer material parameters than are required by the conventional biphasic and triphasic models. This approach has tremendous utility when comparing cartilage of different species and varying healths. Additionally, the viscoelastic models can be easily extended in dynamic analysis and FEA programs.
Cartilage primarily experiences compressive motion during exercise. Therefore, to mimic biological function, a mechanical test should also compress the cartilage. One such test is a viscoelastic stress-relaxation experiment. The Prony and fractional calculus viscoelastic models have shown promise in modeling stress-relaxation of equine articular cartilage. The elastic-viscoelastic correspondence principle is used to extend linear viscoelasticity to the frequency domain. This provides a comparison of articular cartilage based on stored and dissipated moduli. The storage and loss moduli metrics are hypothesized to serve as benchmarks for evaluating osteoarthritic cartilage, and provide guidelines for newly engineered bio-materials.
The main goal of the current study is to test the applicability of modeling articular cartilage with viscoelastic models. A secondary goal is to establish a rigorous set of harvesting techniques that allows access to fresh explants with minimal environmental exposure. With a complex substance like cartilage, it is crucial to avoid unnecessary emph{in vitro} environmental exposure. Additional areas of study include: determining the strain-dependency of the mechanical response, exploring the response of cartilage in different fluid mediums such as saline, synovial fluid, and synthetic substitutes, and studying the time-dependent properties of cartilage during stress-relaxation experiments. Equine stifle joints, which are mechanically analogous to human knees, are harvested and used for analysis in this study. It is believed that the proposed viscoelastic models can model other articulating joints as well. If viscoelastic theory can be used to characterize cartilage, then comparisons can be drawn between real and artificial cartilage, leading to better joint replacement technology.
| Identifer | oai:union.ndltd.org:GATECH/oai:smartech.gatech.edu:1853/47656 |
| Date | 03 April 2013 |
| Creators | Smyth, Patrick A. |
| Publisher | Georgia Institute of Technology |
| Source Sets | Georgia Tech Electronic Thesis and Dissertation Archive |
| Detected Language | English |
| Type | Thesis |
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