Biomedical Engineering Reference
In-Depth Information
100 nm) were produced by repeated dipping/layering of a hydroxyl surface functionalized
substrate in a metal alkoxide solution followed by rinsing, hydrolysis, and drying of the
film coating (see Figure 9.14). The ultrathin layer was stabilized without the need for high
sintering temperatures.
The surface topography, roughness, and composition of ultrathin sol-gel coatings were
investigated by AFM. Bioactivity testing indicated enhanced apatite formation compared
to thicker sol-gel coatings. However, while the ultrathin coatings were more uniform, no
improvements in adhesion strength were observed.
Electrophoretic Deposition
Particles suspended in a solution often carry a net charge. Under the influence of a direct-
current electric field (20-1000 V/cm) these charged particles move toward the oppositely
charged electrode and get deposited as film (Figure 9.15). This is electrophoretic deposi-
tion. These films are essentially a 3-D assembly of particles and thus possess nanostruc-
tured morphology.
Radice and coworkers [40] coated Ti 6 Al 4 V substrates with zirconia-Bioglass ® composite
layers. Composite bilayer coatings on Ti6Al4V substrates were prepared by electrophoretic
deposition. Biocompatible yttrium-stabilized zirconia (YSZ) in the form of nanoparticles
and bioactive Bioglass ® (45S5) in the form of microparticles were chosen as coating mate-
rials. The first layer consisted of 5 μm of YSZ, deposited to avoid any metal tissue con-
tact. The second layer consisted of 15 μm thick 45S5-YSZ composite, which was supposed
to react with the surrounding bone tissue and enhance implant fixation. The adsorption
of YSZ nanoparticles on 45S5 microparticles in organic suspension was found to invert
the surface charge of the 45S5 particles from negative to positive. This enabled cathodic
electrophoretic deposition of 45S5, avoiding uncontrolled anodization (oxidation) of the
substrate. The coatings were sintered at 900°C for 2 h under argon flow to significantly
improve coating adhesion (see Figure 9.15).
Surface
modification
Chemisorption
Hydrolysis
-OH
-OH
-OH
-OH
-O
- -O
-O
OH
O
-O
-O
-O
-O
OBu
OBu
Ti
Ti
OBu
OBu
Ti
Ti
OH
TiOBu4
Toluene/ethanol
(1:1)
Water
Multilayer
(repetition)
-O
-O
-O
-O
OH
OHO
Ti
OH
Ti
O
Ti
Ti
O
HO
OH
Chemisorption
hydrolysis,
drying, etc.
FIGURE 9.14
Chemisorption layering of sol-gel to produce an ultrathin bioactive glass film on titanium alloy substrates [39].
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