Mechanical properties of a new type of glass-ceramic for prosthetic applications

Abstract

Summary—A multiphase glass-ceramic, A-W, precipitating apatite and wollastonite in a glassy matrix can form a tight chemical bond with living bone and has a high mechanical strength. Mechanical properties of the glass-ceramic were investigated in terms of its microstructure. Fracture strength of the parent glass was increased only slightly with the precipitation of the apatite [Ca,10(PO4)6(O,F2)] alone, but remarkably with the precipitation of the wollastonite (CaO-SiO2) in addition to the apatite. The increase in the strength was attributed to the increase in the fracture toughness. The wollastonite might effectively inhibit the straight propagation of cracks on the fracture, causing an increase in the fracture surface energy and thereby the fracture toughness. The magnitude of the mechanical fatigue, i.e. the decrease in the fracture strength with loading, of the parent glass in a simulated body fluid was reduced only slightly with the precipitation of the apatite alone, but remarkably with the precipitation of the wollastonite in addition to the apatite. This means that the wollastonite also effectively suppresses slow crack growth due to stress-induced corrosion. When a bending stress of 65 Mpa is continuously applied in the simulated body fluid, glass-ceramic A-W was estimated to be able to withstand over 10 years whereas the parent glass and the glass-ceramic containing apatite alone fail in 1 min. When glass-ceramic A-W was placed in the simulated body fluid without being loaded, it showed an increase in fracture strength. Practical life-times can be expected to be much more prolonged than those estimated above. The glass-ceramic actually implanted into subcutaneous tissue of rat showed little change in fracture strength even after 12 months. As a result, it can be concluded that glass-ceramic A-W is a promising bioactive material for artificial bone usable even under load-bearing conditions.