Biomedical Engineering Reference
In-Depth Information
geometries
[32-38]
. These sol-gel coatings seem to show potential in the field of dentistry for
improving implants.
9.1.3
Coated HA on Ti6Al4V by Electrophoretic Deposition
The bioceramic, HA, has similar mineral constituents as cortical bone and teeth and is a common
material used to coat metal implants. The HA coating would not only reduce the release of metallic
ions by acting as a barrier, but also enhance the bone bioactivity by virtue of chemical constituents.
Many techniques such as dip coating, ion sputtering, sol-gel coating, pulsed-laser deposition, electro-
phoretic deposition (EPD), and so on, have been proposed to fabricate HA coatings
[39]
. Among the
various fabrication methods, EPD is a promising technique, with advantages including decreased pro-
duction time, simplistic instrumentation, and the capability of coating complex-shaped implants
[40]
.
EPD is a colloidal process which offers easy control of thickness and quality of coating through sim-
ple adjustment of the deposition time, applied potential, and powder morphology
[40]
. The corrosion
behavior of EPD HA coatings on Ti alloys has not been fully studied with respect to morphology and
size of the initial HA particles. Furthermore, HA coatings reinforced with carbon nanotubes (CNTs) was
reported to be a viable route for forming a surface composite with higher hardness, elastic modulus, and
interlaminar shear strength than that of monolithic HA layers
[41]
. The addition of CNTs also helps to
prevent deposited coating layers from peeling-off one substrate by reinforcing the coating material
[41]
.
9.1.4
Double-Layer Glass-Ceramic Coatings on Ti6Al4V
Different coating methods such as enamelling, sputter coating techniques, and vacuum plasma spray
[42-44]
have been applied to coat Ti6Al4V. However, the sputtering and plasma spray techniques
present problems related to the difficulty of coating complex shapes, to eventual compositional
modifications of the coating, and by their high cost. On the contrary, enamelling techniques are very
inexpensive to coat substrates, even complex shapes, and it is easily applicable to glasses and glass-
ceramics because of the peculiar softening properties of these materials. For this reason, bioactive
glasses and glass-ceramics do represent a feasible alternative to HA, commonly used as bioactive
coating on metallic prostheses in order to improve their adhesion with bone.
Double-layer bioactive glass-ceramic coatings were prepared on Ti6Al4V substrates by dipping and
firing. A SiO
2
-CaO-Na
2
O-MgO-P
2
O
5
-K
2
O (SCP)-based glass was used as the first layer in direct con-
tact with the metallic substrate and a SiO
2
-Al
2
O
3
-P
2
O
5
-K
2
O-CaO-F
(SAF)-based glass-ceramic was
used as the outer bioactive layer. The deposition of the intermediate SCP layer was necessary in order to
obtain a good adhesion of the coating to the substrate, to minimize the reactivity between the substrate
and the outer glass-ceramic coating, and thus to preserve the nature of its crystalline phases.
9.2
NANOSTRUCTURED TIO
2
DEPOSITED ON TI6Al4V
Regardless of vast biomedical applications
[45]
, titanium and its alloy form an external superficial
passive oxide film that can reach nanometer (nm) thickness and protect against corrosion
[46]
. It is
well-known that nanostructured materials exhibited a greater surface area than conventional mate-
rials
[47, 48]
, which may significantly influence the corrosion behavior of nano-coatings. In the
current study, researchers utilize nanostructured materials to modify implant surface. For example,
