NMR cryoporometry of porous materials and articular cartilage models
1University of Oulu, Faculty of Science, Physics
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Oulu : K. Tolkkinen,
Articular cartilage is one of the most studied porous biomaterial. It is an essential part of the human body because it makes the movement of the joint smooth and painless. The health of articular cartilage depends on its protein content, pore size and water components and these factors are directly related to progressive cartilage degeneration. Research of articular cartilage is important for development of early diagnosis, prevention and treatment of articular cartilage diseases.
Nuclear magnetic resonance cryoporometry is a non-invasive method for determining pore size distributions of porous materials. The aim of this thesis was to perform proton NMR cryoporometry on salt solutions, porous materials and articular cartilage hydrogels which were very simplified models of articular cartilage protein content. The cartilage gels were composed of collagen, proteoglycans and phosphate-buffered saline. Salt solutions as thermoporometric probe fluids have not been studied extensively and thus the phase transitions of saline and phosphate-buffered saline were studied. The results obtained from the cryoporometry experiments of salt solutions and porous silica gels were used to interpret the results of protein gel experiments. The end goal of the experiments was to estimate the pore size distributions of protein gels, identify which protein components water is associated with in articular cartilage, and measure the associated T2 relaxation times.
As a result, it was observed that there occur two separate phase transitions in salt solutions during melting: the eutectic phase transition and the bulk melting. It was also found that both transitions occur over a certain temperature range instead of one specific temperature. Cryoporometry of silica gels imbibed with water or saline showed that the melting behavior of solutions were different which affected the computed pore size distributions. In conclusion, NMR cryoporometry of salt solutions is complex and traditional data interpretation cannot be applied.
The study of articular cartilage gels showed that the eutectic transition of phosphate-buffered saline and the wide temperature range of bulk melting caused additional peaks in the pore size distributions. By performing data analysis with two different methods, the peaks associated with both proteins were identified and pore size distribution was estimated to be approximately 2–5 nm. However, completely accurate information on pore size could not be determined by this method. T2 relaxation time measurements showed that T2 is dependent on the amount of collagen but not on the amount of proteoglycans at room temperature.
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