Evaluating the In Vitro Corrosion Behavior and Cytotoxicity of Vapor Deposited Magnesium Alloys

Open Access
- Author:
- Petrilli, John David
- Graduate Program:
- Engineering Science
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- April 03, 2009
- Committee Members:
- Barbara Shaw, Thesis Advisor/Co-Advisor
Barbara Shaw, Thesis Advisor/Co-Advisor - Keywords:
- HBSS
magnesium
corrosion
PVD
simulated body fluid (SBF) - Abstract:
- Magnesium alloys are emerging as a promising class of bioabsorbable implant materials due to magnesium’s biocompatibility and propensity for corrosion. These alloys are useful for implants like cardiac stents. Stents only need to support a diseased blood vessel while it heals, but their permanent presence has been linked with medical complications. Bioabsorbable magnesium stents have therefore been developed, but clinical trials with stents made of magnesium alloy WE43 have shown that they corrode before the healing process is complete. This thesis therefore proposes physical vapor deposition (PVD) as a means of fabricating nonequilibrium magnesium alloys with improved corrosion resistance. XRD analysis of PVD alloys containing yttrium and titanium showed preferential Mg (002) orientation, but alloying elements remained in solid solution. Electrochemical methods were used to test both PVD magnesium alloys and commercial WE43 under in vitro conditions in 37ºC Hanks Balanced Salt Solution (HBSS). Results showed that the PVD alloys exhibited superior corrosion resistance to WE43, especially after aging for several months to one year. Experimental evidence did not indicate that the surface oxide was responsible for the increased corrosion resistance after aging, so it was attributed to stress relief annealing at room temperature. In addition, transformed A549 cells were cultured on magnesium alloys to assess the alloys’ in vitro cytotoxicity. Cells grown on WE43 were observed to demonstrate indeterminate or apoptotic morphologies, but cells grown on PVD alloys with low (< 15 μA/cm2) corrosion rates were observed to be viable. These cells demonstrated healthy morphologies and grew to form partial monolayers over the PVD alloys’ surfaces. An aged PVD alloy containing 2 wt% titanium was observed to demonstrate a lower corrosion rate, comparable passive current density, higher breakdown potential, larger passive region, and lower cytotoxicity than commercial alloy WE43.