Biodegradable phosphorus-modified Mg2Ge/Mg-Cu composite with good angiogenic, osteogenic, and antibacterial functionalities for bone-fixation applications

Magnesium (Mg)-based composites are expected to be useful for biodegradable bone-implant materials due to their degradability, similar elastic modulus to that of bone, and biofunctionalities. However, their rapid degradation, poor biotribology performance, and lack of vascularization and antibacterial activity are not conducive to bone-fixation applications. In this study, an in situ Mg₂Ge/Mg-Cu-P composite with a nominal composition of Mg-10Ge-2Cu-0.5P (denoted MGCP) was prepared via phosphorus (P)-modified casting followed by hot extrusion for biodegradable bone-fixation applications. For comparison, an in situ Mg₂Ge/Mg-Cu composite (Mg-10Ge-2Cu, denoted MGC) was prepared under the same conditions without P-modification. The hot-extruded (HE) MGCP sample showed significantly improved corrosion resistance with corrosion rates of 2.2 mm/y and 2.51 mm/y as measured by potentiodynamic-polarization and hydrogen-release testing in Dulbecco’s Modified Eagle Medium supplemented with fetal bovine serum (denoted DMEM). The HE MGCP also exhibited notably enhanced mechanical properties and biotribological resistance in DMEM, with an σ_UTS of ∼304.2 MPa, σ_TYS of ∼202.5 MPa, elongation of ∼12.3%, σ_UCS of 769.0 MPa, σ_CYS of 208.0 MPa, and Brinell hardness of 105.3 HB, along with smaller σ_TYS and σ_CYS decreases after 3 d of immersion in Hanks’ solution. In comparison to pure titanium and Mg, the HE MGCP demonstrated much greater cytocompatibility, angiogenic capacity, and osteogenic differentiation and mineralization capability. Furthermore, the HE MGCP displayed markedly higher in vitro antibacterial activity, in vivo antibacterial and anti-inflammatory ability, and good biosafety in a rat subcutaneous-implantation model compared to pure titanium and Mg, indicating significant potential for biodegradable bone-fixation applications.