title: Electrochemical characteristics of bioresorbable binary MgCa alloys in Ringer's solution: Revealing the impact of local pH distributions during in-vitro dissolution.
abstract: Biodegradable magnesium-calcium (MgCa) alloy is a very attractive biomaterial. Two MgCa alloys below the solid solubility of Ca were considered, as to solely investigate the effect of Ca content on the behavior of magnesium and the pH changes associated to metal dissolution. X-ray diffraction analysis and optical microscopy showed that both Mg-0.63Ca and Mg-0.89Ca alloys were solely composed of α(Mg) phase. Degradation characteristics and electrochemical characterization of MgCa alloys were investigated during exposure to Ringer's solution at 37 °C by electrochemical impedance spectroscopy and scanning electrochemical microscopy. The impedance behavior showed both capacitive and inductive features that are related to the alloy charge transfer reaction and the relaxation of the absorbed corrosion compounds, and can be described in terms of an equivalent circuit. Scanning electron microscopy (SEM) was employed to view the surface morphology of the MgCa samples after 1 week immersion in Ringer's solution showing extensive precipitation of corrosion products, whereas the substrate shows evidence of a non-uniform corrosion process. Energy dispersive analysis showed that the precipitates contained oxygen, calcium, magnesium and chlorine, and the Mg:Ca ratios were smaller than in the alloys. Scanning electrochemical microscopy (SECM) was used to visualize local pH changes associated to these physicochemical processes with high spatial resolution. The occurrence of pH variations in excess of 3 units between anodic and cathodic half-cell reactions was monitored in situ.
authors.affiliation: Faculty of Chemical Engineering and Environmental Protection, The "Gheorghe Asachi" Technical University of Iasi, 700050, Iasi, Romania. Electronic address: danmareci@yahoo.com.
authors.forename: D
authors.initials: D
authors.lastname: Mareci
authors.affiliation: Faculty of Chemical Engineering and Environmental Protection, The "Gheorghe Asachi" Technical University of Iasi, 700050, Iasi, Romania.
authors.forename: G
authors.initials: G
authors.lastname: Bolat
authors.affiliation: Department of Chemistry, University of La Laguna, P.O. Box 456, E-38200 La Laguna (Tenerife), Spain.
authors.forename: J
authors.initials: J
authors.lastname: Izquierdo
authors.affiliation: Faculty of Mechanical Engineering, The "Gheorghe Asachi" Technical University of Iasi, 700050, Iasi, Romania.
authors.forename: C
authors.initials: C
authors.lastname: Crimu
authors.affiliation: Faculty of Mechanical Engineering, The "Gheorghe Asachi" Technical University of Iasi, 700050, Iasi, Romania.
authors.forename: C
authors.initials: C
authors.lastname: Munteanu
authors.affiliation: Faculty of Materials Science and Engineering, Politehnica of Bucharest, 060042 Bucharest, Romania.
authors.forename: I
authors.initials: I
authors.lastname: Antoniac
authors.affiliation: Department of Chemistry, University of La Laguna, P.O. Box 456, E-38200 La Laguna (Tenerife), Spain; Faculty of Materials Science and Engineering, Politehnica of Bucharest, 060042 Bucharest, Romania. Electronic address: rsouto@ull.es.
authors.forename: R M
authors.initials: RM
authors.lastname: Souto
mesh_terms: D020341:Absorbable Implants; D000497:Alloys / Q000737:chemistry*; D001672:Biocompatible Materials / Q000737:chemistry; D002118:Calcium / Q000737:chemistry*; D003343:Corrosion; D007552:Isotonic Solutions / Q000737:chemistry*; D008274:Magnesium / Q000737:chemistry*; D008855:Microscopy, Electron, Scanning; D000077331:Ringer's Solution; D013499:Surface Properties
chemical_list: D000497:Alloys; D001672:Biocompatible Materials; D007552:Isotonic Solutions; D000077331:Ringer's Solution; D008274:Magnesium; D002118:Calcium
keywords: Corrosion resistance; EIS; Electrochemical characterization; Local pH distributions; MgCa alloys; SECM; SEM; XRD