Influence of HEPES buffer on the local pH and formation of surface layer during in vitro degradation tests of magnesium in DMEM

Journal article (2014)
Department
Materials Science and Engineering (Mechanical, Maritime and Materials Engineering) (TU Delft)
Copyright: © 2014 Chinese Materials Research Society
DOI: https://doi.org/doi:10.1016/j.pnsc.2014.08.009
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Published Date

18-10-2014

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Source:

Progress in Natural Science: Materials International, 24, 2014

Faculty

Mechanical, Maritime and Materials Engineering

Department

Materials Science and Engineering

Abstract

The human body is a buffered environment where pH is effectively maintained. HEPES is a biological buffer often used to mimic the buffering activity of the body in in vitro studies on the degradation behavior of magnesium. However, the influence of HEPES on the degradation behavior of magnesium in the DMEM pseudo-physiological solution has not yet been determined. The research aimed at elucidating the degradation mechanisms of magnesium in DMEM with and without HEPES. The morphologies and compositions of surface layers formed during in vitro degradation tests for 15–3600 s were characterized. The effect of HEPES on the electrochemical behavior and corrosion tendency was determined by performing electrochemical tests. HEPES indeed retained the local pH, leading to intense intergranular/interparticle corrosion of magnesium made from powder and an increased degradation rate. This was attributed to an interconnected network of cracks formed at the original powder particle boundaries and grain boundaries in the surface layer, which provided pathways for the corrosive medium to interact continuously with the internal surfaces and promoted further dissolution. Surface analysis revealed significantly reduced amounts of precipitated calcium phosphates due to the buffering activity of HEPES so that magnesium became less well protected in the buffered environment.