Biomedical Engineering Reference
In-Depth Information
Figure 4.10
Shows how a plasma-sprayed HA coating on a porous
titanium (dark bars) dependent on the implantation time will
improve the interfacial bond strength compared to uncoated
porous titanium (light bars). Reprinted from Ref. [49] with
permission.
A number of factors appeared to influence the properties of
calcium orthophosphate coatings. They include coating thickness
(this will influence coating adhesion and fixation—the agreed
optimum now seems to be within 50-100 µm), crystallinity (this
affects the dissolution and biological behavior), phase and chemical
purity, porosity and adhesion [526, 538]. Methods for the production
of coatings and their properties are now largely standardized and,
over recent years, calcium orthophosphate-coated implants have
found highly successful clinical application, particularly in younger
patients [520-572]. Further details on calcium orthophosphate
coatings might be found in excellent reviews [573, 574].
4.5.3
Functionally Graded Bioceramics
In general, functionally gradient materials (FGMs) are defined as
the materials, having gradient either compositional or structural
changes from their surface to the interior of the materials. The
idea of FGMs allows one device to possess two different properties.
One of the most important combinations for the biomedical field
is that of a mechanical strength and biocompatibility. Namely, only
surface properties govern a biocompatibility of the entire device.
In contrast, the strongest material determines the mechanical
strength of the entire device. Although, this subject belongs to the
coatings section (see above), in a certain sense, metallic implants
covered by calcium orthophosphates might be considered as a FGM.
The surface shows excellent biocompatibility because it consists
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