Development and testing of biodegradable metallic stents
Chen, Pauline Yunwei.
Date of Issue2009
School of Mechanical and Aerospace Engineering
A biodegradable esophageal stent is investigated and designed. For the design phase, the key design feature is its double C-shape allowing it to bend to smaller diameter and return to its original diameter upon deployment hence letting it pass through the esophagus easily. For the investigation phase, immersion tests are conducted; samples of AZ31 are polished, weighed and immersed in pH 2 to pH 10 physiological saline solutions (PSS) and maintained at 37oC for up to 28 days. After immersion test, samples are cleaned, dried and weighed. Graphs of mass degradation against immersion time and pH value of PSS are plotted and studied. Scanning Electron Microscope (SEM), Fourier Transform Infra-red Spectrometer (FTIR) and X-ray Diffractometer (XRD) are used to analyze the degraded samples. Mass degradation increases overtime; higher degradation rates at the start and gradually decreases with immersion time. Acidic conditions create higher tendency for degradation to occur hence stent degradation can be controlled by consuming alkaline or acidic fluids to decrease or increase stent degradation respectively. Mass degradation is non-uniform creating porous surface. At < pH 7 conditions, more corrosion products produced led to rougher surfaces. On the other hand, precipitation creates fibers on the surface; size of fibers increases as immersion time increases. Therefore, the two competing processes (i.e. mass degradation and precipitation) modify the surface resulting in porous surface with thicker fibers. Carbonates (CO3), hydroxyl groups (OH) and water molecules (H2O) are identified by the FTIR. These compositions are not affected by pH conditions while at < 0.25 days less corrosion products are observed. Magnesium hydroxide, Mg(OH)2, is identified by XRD as the main composition of the corrosion product and it is not affected by pH conditions. Other possible corrosion products are not detectable by the XRD.
Final Year Project (FYP)
Nanyang Technological University