MAGNESIUM ALLOYS AS A BIORESORBABLE IMPLANT MATERIAL

UoM administered thesis: Doctor of Engineering

  • Authors:
  • Robert Thornton

Abstract

The use of magnesium as a bioresorbable implant material has been gaining largeamounts of interest over the last five years. Mg alloys by nature corrode rapidly comparativeto other engineering metals, Mg is also naturally found in the body, meaningit offers a potential degradable material which can support far higher stresses than thecurrent biodegradable polymers. Magnesium Elektron wanted to gain an understandingof how Mg alloys would work in this new environment and find a potential alloy fit forpurpose. This thesis outlines the progress the author and Magnesium Elektron have madein 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 Mgalloys. These studies showed that high corrosion rates initially seen when Mg alloys areplaced in cell culture medium have a lower cell numbers. Most likely due to local pHrise. 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 proliferateand attach well. The attached cells on Mg also showed a phenotype expression changecompared to those on glass.It was then established that lowering the corrosion rate of the current Mg alloys wasnow key. Initially this involved modifications to current alloys. Annealing ML4 at 350Cfor 8 hours was found optimal and lowered corrosion rates by 20-30%. Further worklooked at modifing alloys by changes to chemical composition. It was discoveredd thatadditions of 8wt% Er to ML4 made corrosion rates drop by 6-8 times in SBF. Additionsof Gd in ML4 also gave low corrosion, 2 times less than ML4. Calcium also loweredcorrosion rates slightly.The modifications to the Mg surface was also looked into to lower the initial corrosionrate and potentially alter the biocompatibility of the alloys. Two successful techniqueswere found. Firstly organo-silanes were found to protect Mg for around 4 days, with reductionsin corrosion rate of 6 times in the first hours. Silanes were also successfully usedas anchors to graft polythene gycol to create a non fouling surface, which could protentiallylower stent restenosis Secondly, Magnetron sputtered hydroxyapatite was used tolower corrosion rates by 6 times in the first 24 hours with no visible hydrogen gas beingevolved in the first hours.

Details

Original languageEnglish
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Supervisors/Advisors
Award date1 Aug 2011