title: Biocompatibility and biodegradability of Mg-Sr alloys: the formation of Sr-substituted hydroxyapatite.
abstract: Magnesium is an attractive material for use in biodegradable implants due to its low density, non-toxicity and mechanical properties similar to those of human tissue such as bone. Its biocompatibility makes it amenable for use in a wide range of applications from bone to cardiovascular implants. Here we investigated the corrosion rate in simulated body fluid (SBF) of a series of Mg-Sr alloys, with Sr in the range of 0.3-2.5%, and found that the Mg-0.5 Sr alloy showed the slowest corrosion rate. The degradation rate from this alloy indicated that the daily Sr intake from a typical stent would be 0.01-0.02 mg day⁻¹, which is well below the maximum daily Sr intake levels of 4 mg day⁻¹. Indirect cytotoxicity assays using human umbilical vascular endothelial cells indicated that Mg-0.5 Sr extraction medium did not cause any toxicity or detrimental effect on the viability of the cells. Finally, a tubular Mg-0.5 Sr stent sample, along with a WE43 control stent, was implanted into the right and left dog femoral artery. No thrombosis effect was observed in the Mg-0.5 Sr stent after 3 weeks of implantation while the WE43 stent thrombosed. X-ray diffraction demonstrated the formation of hydroxyapatite and Mg(OH)₂ as a result of the degradation of Mg-0.5 Sr alloy after 3 days in SBF. X-ray photoelectron spectroscopy further showed the possibility of the formation of a hydroxyapatite Sr-substituted layer that presents as a thin layer at the interface between the Mg-0.5 Sr alloy and the corrosion products. We believe that this interfacial layer stabilizes the surface of the Mg-0.5 Sr alloy, and slows down its degradation rate over time.
authors.affiliation: Light Metals and Advanced Magnesium Materials, Mining & Materials Engineering, McGill University, Montreal, QC H3A 2B2, Canada. mandana.bornapour@mail.mcgill.ca
authors.forename: M
authors.initials: M
authors.lastname: Bornapour
authors.forename: N
authors.initials: N
authors.lastname: Muja
authors.forename: D
authors.initials: D
authors.lastname: Shum-Tim
authors.forename: M
authors.initials: M
authors.lastname: Cerruti
authors.forename: M
authors.initials: M
authors.lastname: Pekguleryuz
mesh_terms: D020341:Absorbable Implants; D000497:Alloys / Q000494:pharmacology*; D000818:Animals; D001672:Biocompatible Materials / Q000494:pharmacology*; D001826:Body Fluids / Q000187:drug effects; D016923:Cell Death / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D003343:Corrosion; D004285:Dogs; D017886:Durapatite / Q000494:pharmacology*; D005263:Femoral Artery / Q000187:drug effects / Q000648:ultrastructure; D061307:Human Umbilical Vein Endothelial Cells / Q000166:cytology / Q000187:drug effects; D006801:Humans; D006863:Hydrogen-Ion Concentration / Q000187:drug effects; D020007:Implants, Experimental; D008422:Materials Testing; D056951:Photoelectron Spectroscopy; D013052:Spectrometry, X-Ray Emission; D013324:Strontium / Q000494:pharmacology*; D013499:Surface Properties; D014961:X-Ray Diffraction
chemical_list: D000497:Alloys; D001672:Biocompatible Materials; C573915:Mg-Sr alloy; D017886:Durapatite; D013324:Strontium