Preparation and characterization of biodegradable Mg-Zn-Ca/MgO nanocomposites for biomedical applications

Highlights: • Novel biodegradable Mg-Zn-Ca/MgO matrix composites, were devised and prepared using high shear melt conditioning. • The excellent interfacial bonding between MgO particles and α-Mg matrix was observed via HRTEM and FFT pattern analysis. • The optimum solution treatment and the addition of MgO nanoparticles hugely enhanced corrosion resistance of nanocomposites. • The yield tensile strength (YTS) increased by 22.81% with 0.5% MgO addition, while the ductility did not mainly deteriorate. - Abstract: In order to improve the corrosion resistance and mechanical properties of magnesium alloys for biomedical implant applications, novel biodegradable Mg-3Zn-0.2Ca (wt%) matrix composites, reinforced by adding various contents of MgO nanoparticles (0.1, 0.2, 0.3, 0.5 wt%), were devised and prepared using high shear melt conditioning. An optimum solution treatment (450 °C, 48 h) and subsequent hot extrusion was carried out to produce the Mg-3Zn-0.2Ca/MgO composites. It was found that the as-extruded composite exhibited a fine grain structure with relatively uniformly distributed MgO particles. The orientation relationships (ORs) of (1 1 1)_MgO ~ 2.62° from (0 0 0 2)_α-Mg and [0 −1 1]_MgO // [2 −1 −1 0]_α-Mg, were observed between the MgO particles and the α-Mg matrix via high resolution transmission electron microscopy (HRTEM) investigation and fast Fourier transform (FFT) pattern analysis, verifying the excellent interfacial bonding between the phases. Additionally, a substantial reduction in the secondary phase content was found in the solution treated sample. In vitro immersion, electrochemical, and mechanical tensile tests were used to characterize the corrosion behavior and mechanical properties. The ultimate tensile strength (UTS) increased to 329.03 ± 2.01 MPa and the yield tensile strength (YTS) increased by 22.81% with 0.5 wt% MgO loading, while the ductility did not substantially deteriorate. The polarization resistance (R_p) of the composite was shown to increase from 0.95 kΩ cm² to 2.02 kΩ cm² with the addition of 0.2 wt% MgO. With increasing MgO content, agglomeration of the MgO particles was detected in the analyzed composite, resulting in decreased ductility and the occurrence of pitting corrosion.