Biomedical Engineering Reference
In-Depth Information
Glass coating
Ceramic substrate
Figure 8.1
Schematic of a diamond-shaped hardness indenter with one of its
diagonals on the interface of a coating and the substrate.
situations involved, a more exhaustive characterization is needed to
predict the
in vivo
response of the interfaces. However, indentation
testing is an attractive alternative to more costly fracture mechanics
experiments for determining, in a preliminary way, the adhesion between
two materials. This comparative method is based on measurements of the
resistance toward propagation of a crack along an interface: cracks can
be introduced by Vickers indentations and observed by scanning electron
microscopy. The resistance to crack propagation provides a qualitative
measurement of the strength of a brittle material. The induced radial
cracks propagate in a direction parallel to the indentation diagonals and
normal to the specimen surface. When the indentations are performed
at the substrate-coating interface, with one of the diagonals near or just
on the ''border line'' between the two materials (Figure 8.1), the crack
propagation gives qualitative information about the fracture energy
of the two joined materials and about the fracture energy of their
interface. The crack path will propagate into the weaker material or
it will follow the most weakly bonded interface. If the bonding at the
interface is stronger than the coating, the crack would propagate through
the coating.
Osteointegration of bioactive glass-coated zirconia cylinders has been
evaluated in an animal model and compared to uncoated cylinders [8].
After 30 and 60 days, bone bonding was better to the coated cylinders,
but after 60 days the difference was within the statistical uncertainty.
