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Title: Magnesium alloys as a bioresorbable implant material
Author: Thornton, Robert
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2011
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The use of magnesium as a bioresorbable implant material has been gaining large amounts of interest over the last five years. Mg alloys by nature corrode rapidly comparative to other engineering metals, Mg is also naturally found in the body, meaning it offers a potential degradable material which can support far higher stresses than the current biodegradable polymers. Magnesium Elektron wanted to gain an understanding of how Mg alloys would work in this new environment and find a potential alloy fit for purpose. This thesis outlines the progress the author and Magnesium Elektron have made in achieving those goals. Initally, to form an understanding of what occurs when Mg is implanted into the body. Osteoblast trials were used to determine in vitro responses and effects on the various Mg alloys. These studies showed that high corrosion rates initially seen when Mg alloys are placed in cell culture medium have a lower cell numbers. Most likely due to local pH rise. The effect is inherent to all Mg alloys irrespective of their overall corrosion rate. However, after the initial corrosion spike, surviving cells on the surface would proliferate and attach well. The attached cells on Mg also showed a phenotype expression change compared to those on glass. It was then established that lowering the corrosion rate of the current Mg alloys was now key. Initially this involved modifications to current alloys. Annealing ML4 at 350°C for 8 hours was found optimal and lowered corrosion rates by 20-30%. Further work looked at modifing alloys by changes to chemical composition. It was discoveredd that additions of 8wt% Er to ML4 made corrosion rates drop by 6-8 times in SBF. Additions of Gd in ML4 also gave low corrosion, 2 times less than ML4. Calcium also lowered corrosion rates slightly. The modifications to the Mg surface was also looked into to lower the initial corrosion rate and potentially alter the biocompatibility of the alloys. Two successful techniques were found. Firstly organo-silanes were found to protect Mg for around 4 days, with reductions in corrosion rate of 6 times in the first hours. Silanes were also successfully used as anchors to graft polythene gycol to create a non fouling surface, which could protentially lower stent restenosis. Secondly, Magnetron sputtered hydroxyapatite was used to lower corrosion rates by 6 times in the first 24 hours with no visible hydrogen gas being evolved in the first hours.
Supervisor: Gough, Julie Sponsor: Not available
Qualification Name: Thesis (Eng.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Magnesium ; Resorbable