Mg Corrosion Control By Biopolymer-Polyelectrolyte Membranes

Mg and Mg alloys offer a great potential for use as a biomedical material for temporary implant applications: its lack of toxicity, ability to easily dissolve in aqueous environments, and its bone-like bulk properties. One of the key drawbacks however, that prevents the more widespread use of magnesium-based materials is their fast and often uncontrollable corrosion within the human body that impedes its utilisation in a wide range of orthopaedic components^1,2. The possibility to control this dissolution is vital if Mg alloys are to be considered as a practical, temporary biomedical implant materials. In this study we detail how this aim can be attained by the use of biocompatible polymeric membrane materials. For example, by using a polyelectrolyte like poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) to modify cellulose acetate (CA) membranes it is possible to achieve Mg dissolution control.

Commercially pure magnesium surfaces were spin-coated with differing concentrations of PDMAEMA to create a number of cellulose based surfaces that were subsequently exposed to an aqueous solution. On immersion it was observed that the CA film distends and begins to function like a membrane that can control both ion flow and H₂ gas evolution. Electrochemical measurements (open circuit potential, polarisation and linear sweep voltammograms) demonstrate that by varying the CA:PDMAEMA ratio, the rate of Mg corrosion can be controlled. Additional measurements of pH and with ICP-OES clearly demonstrate that the accumulation of corrosion products between the membrane and the sample also reduces the undesirable effects of H₂ formation and high local pH that takes place during the corrosion process³.

Furthermore, SECM studies (with ferrocenemethanol as a redox mediator and using a custom-made cell set-up) were performed in order to determine membrane permeability: knowledge over the permeability of the membrane is crucial when designing the membrane for dissolution control.

Overall, these findings demonstrate that the presence of polyelectrolyte modified cellulose membranes have the potential to control Mg corrosion in physiological environments and that the permeability of the membrane can be controlled by additions of a cationic polyelectrolyte like PDMAEMA.   

(1) F. Witte, N. Hort, C. Vogt, S. Cohen, K. U. Kainer, R. Willumeit, F. Feyerabend, Current Opinion in Solid State and Materials Science, 2008, 12, 63-72.

(2) S. Virtanen, Mater. Sci. Eng. B, 2011, 176, 1600-1608.

(3) K. Yliniemi, B. P. Wilson, F. Singer, S. Höhn, E. Kontturi S. Virtanen, ACS Applied Materials and Interfaces, 2014, 6, 22393-22399.