| dc.description.abstract | Mg-based bulk metallic glass(BMG) and its composites have been investigated for their huge potential for application in orthopedic implants due to their biocompatibility, low degradation rate, and osteogenetic ability. However, the intrinsic brittleness of Mg-Zn-Ca BMG has to be significantly improved for commercial application. Therefore, the concept of ex-situ adding metallic particles is introduced to produce Mg-Zn-Ca bulk metal glass composite (BMGC) to meet the requirement of mechanical properties. In this study, the Mg66Zn29Ca5 BMG was selected as base alloy and added different micro-spherical metal particles (Fe, porous Mo and TiZr-based metallic glass powder) to enhance its fracture toughness. The optima results occur at 3 mm Mg-Zn-Ca BMGC rods with 20vol.% porous Mo particles, the fracture toughness increased up to 6.1 MPa‧m1/2 from 1.1 MPa‧m1/2 of based and remained the compressive strength of 672 MPa. However, 4mm size rods were unstable structures combined with amorphous and crystalline structures due to the insufficient cooling rate. Therefore, we design a core-shell structure comprising a pure Mg crystalline core and amorphous shell in order to overcome the size limit imposed by the cooling rate effects. As a result, the shell of 4mm core-shell Mg BMG rods exhibits fully amorphous shell and have a lower degradation rate after six weeks of degradation. Moreover, the biocompatibility and osteogenic effects were similar between the core–shell and solid structures of Mg-based BMG. In conclusion, the core–shell structure of Mg-based BMG exhibits suitable mechanical properties and lower degradation rate while still enhancing osteogenic potential in vitro.
As an orthopedic implant, initial cell adhesion was a critical issue for subsequent osteogenesis and bone formation because the first contact between cells and the implant occurs upon the implants surface. Three different surface roughness of Mg-based BMG samples were designed to understand the degradation behavior of Mg-based BMG and the adhesion ability and osteogenetic ability of the contact cells. The surface roughness could not affect the degradation behavior of Mg66Zn29Ca5 BMG. The surface polished via #800 grade sandpaper possessed well-attached surface and a good cell viability environment for MG63 osteoblast-like cells. Moreover, higher surface roughness was investigated more calcium and mineral deposition which verify the relationship between surface roughness and cell performance.
The Mg-Zn-Ca metallic glass thin film (MGTF) was coated on the surface of ZK60 substrate improve its mechanical properties, corrosion resistance and biocompatibility. Through the DC vacuum sputtering machine, the Mg-based metallic glass coating was successfully coated on the ZK60 substrate, and the structure of the Mg-based metallic glass coating remained amorphous. The results of coating adhesion test show that the Mg-based metallic glass coating possess high adhesion property with 5B grade of tape testing (0% of the film peels off from the substrate). Meanwhile, the hardness of the Mg-based metallic glass coating can reach to 240 Hv by nano-indentation. Through the three-point bending testing, the Mg-based metallic glass thin film MGTF coating with 1000 nm thickness can effectively improve the bending strength about from 216 MPa to 254 MPa. In addition, the results of electrochemical corrosion test present that the Mg-based metallic glass MGTF coating prepared by 30W sputtering possessed the best corrosion resistance. The corrosion current in 30W power was 1.66 × 10-6 A/cm2, which is much lower than the ZK60 alloy (2.88 × 10-5 A/cm2). | en_US |