| Summary: | 碩士 === 國立臺灣大學 === 醫學工程學研究所 === 90 === Phase transition plays a very important role in the preparation of membranes by the immersion precipitation process. The phase diagram of Ethanol-methylene chloride-PLLA could be observed by cloud point method，and the gel points and part of binodal boundary could be obtained. Utilization of the theory of Flory-Huggins could assist us approach experimental phase diagram.
The membrane structure could be observed by the scanning electron microscope. The membrane structure was porous when the polymer solution was in low concentration region. Increasing the concentration of polymer solution, the top layer of membrane becomes a particulate structure.
Therefore, we could conclud that the lower concentration area was across the binodal region , the membrane formation was governed by liquid-liquid demixing behavior. The higher concentration area was across the crystal region , the membrane formation was governed by crystallization behavior.
To go a step further the in vitro degradation of three kinds of Poly(L-lactic acid)(PLLA) membranes with different morphologies during a long term period in PBS and H2O2 solution at 37℃. The degradation of these membranes were studied by measuring these changes in mass, molecular weight, molecular weight distribution and crystallinity. As the result, the crystallinity affected the degradation rate. To compare the degradation rate of three kinds of membranes, the result reveals that the dense membrane was fast than others. As the two kinds of degradation environment results, we suggest that the degradation mechanism of PLLA membranes could be separate into two steps.The first step was the chain scission，and the second step was the decrease in Mw and the release of some of the degradation products.
To go a step futher, the attachment and growth of osteoblast cell lines (MG-63) on the three kinds of PLLA membranes were studied with a cell culture method. The cell culture results reveal us the particulate membrane had better biocompatibility than other two membranes. We suggest that the reason was the surface of particulate membrane was roughness and it could provide an environment as three dimensions for cells.
As the degradation rate of particulate membrane was the slowest and the biocompatibility was the best, the particulate PLLA membrane will be suitable of long term of orthopedic implant.
The result of this study showed that the phase diagram could help us to anticipate the structure of membranes and we could use different precipation to control the degradation rate.
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