Theses and Dissertations at Montana State University (MSU)
Permanent URI for this collectionhttps://scholarworks.montana.edu/handle/1/733
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Item Improving osseointegration of PEEK through surface textures(Montana State University - Bozeman, College of Engineering, 2019) Scott, Renn Patrick; Chairperson, Graduate Committee: Cecily RyanPEEK (Polyetheretherketone) is one of the most promising alternatives to titanium in cortical bone implants due to being biologically inert and having an elastic modulus similar to that of bone. It also has favorable reactions conducive to common medical imaging methods such as X-ray and magnetic resonance imaging (MRI) as compared to commonly used metals such as titanium and stainless steel. However PEEK is not inherently osseoconductive, leading to longer healing times and a greater chance of infection. Many different methods exist for improving osteoblast growth, such as the addition of bio-active materials like hydroxyapatite. Manipulating the surface texture of PEEK could provide better environments for cells to attach and can be used as another layer with other techniques, making the tissue interface more robust. The main objective of this project is to observe cell adhesion to a textured surface to identify cell preference for surface geometry as a first step to improve full integration of non-resorbable implants into bone tissue. The methods explored were also chosen for their repeatability, reliability and lack of chemical modification compared to other successful surface modulation techniques. The surface textures were embossed into PEEK using micro-etched aluminum molds. Textures vary in their shape, spacing, size, depth and surface convexity/concavity. The cell adhesion was recorded through fluorescent confocal microscopy and the cell-substrate interaction was observed under electron microscopy. The results were that 25 micron and 10 micron features discouraged cell adhesion while 325 micron and 120 micron features encouraged cell adhesion with pillars performing better than holes. The best feature was the 325x40 micron square pillars. With a cell volume to surface area ratio of 5.13, a live cell count of 276.5, a dead cell count of 9.00, and a non-dimensional distance to feature of 0.67.Item The interstitial fluid pressure response during stress-relaxation of articular cartilage due to viscosity and porous media effects: a computational study(Montana State University - Bozeman, College of Engineering, 2018) Paschke, Brandon James; Chairperson, Graduate Committee: Erick JohnsonArticular cartilage is a complex material made of several fluid and solid components. A model that fully describes the responses of cartilage is required to accurately create a cartilage replacement that can be used in cases of injury or disease. Modeling of articular cartilage has proven difficult and currently no constitutive law fully describes its solid and fluid responses. Many of the current models describe the interstitial fluid as inviscid, even though it is known that proteoglycan migration within cartilage causes a viscous response within interstitial fluid. The goal of this research was to create a viscous fluid porous media model that better captures the compressive resistance of cartilage created by migration of interstitial fluid during cartilage compression. Through the creation of this model it was possible to capture the experimental magnitudes of fluid pressure within cartilage during unconfined slow compression simulations. As part of this model, a porous media approximation was used, which demonstrates that small variations in the solid matrix, comprised of collagen fibers, can cause large variations in system response. Magnitudes of mean pressure values, after 150 seconds of compression, for the viscous fluid porous media model bound the values found in experimental testing. Limitations of the fluid model are that system relaxation isn't captured and the slope increase of pressures during compression for experiments don't match those of the fluid model. A main conclusion drawn from the model is that viscosity of interstitial fluid plays a large role in creating compressive resistance within articular cartilage. Another takeaway is that the porous media approximation greatly impacts the magnitude of fluid pressurization, which creates a need to accurately represent the solid matrix within cartilage.