Among the bioresorbable Mg-based alloys reported, the most
notable is the amorphous Mg-BMG based upon Mg–Zn–Ca. Extract
and direct contact cytotoxicity tests using L929 murine fibroblasts
and MG63 human osteosarcoma cells have shown improved cell
viabilities compared with pure Mg [15]. Furthermore, in vivo
assessment in the abdomen of domestic pigs revealed no significant
hydrogen evolution [16]. Early attempts, in the first half of
the 20th century, to use crystalline Mg as a biomaterial were abandoned
owing to hydrogen evolution, which resulted in the formation
of subcutaneous gas bubbles [5,17]. The combination of
biocompatible elements, immunity to intergranular corrosion and
reduced hydrogen evolution makes Mg-BMG a potentially superior
implant material to crystalline Mg alloys. However, the glassforming
ability (GFA) of Mg–Zn–Ca BMG is poor, with a critical
casting thickness of only 3 mm reported for Mg66Zn30Ca4 and
Mg67Zn28Ca5 (at.%) [1,16]. In addition, the thermoplastic forming
(TPF) window of these alloys is only 20 C. At 135 C, which is
10 C below the first crystallization reaction, there is only 160 s
of processing time available before the onset of crystallization.
The ability of BMG to be net-shaped by TPF techniques is one of
the biggest advantages of these emerging materials. TPF can only
be carried out in the temperature window above the glass transition
and below first crystallization. The large SCL region of BMG
is useful, since there is a significant decrease in viscosity with
increasing deformation temperature that allows these materials
to be plastically deformed to very large strains [18,19]. As a result,