Biomedical Engineering Reference
In-Depth Information
(a)
Laser
Rotating target
carousel
Substrate
Heatable
sample stage
Laser plume
Target
(e.g., bioactive glass)
Vacuum chamber
(b)
IMAT 09 25.0 kV ×1.00 k 30.0 µm
IMAT 04 25.0 kV ×1.00 k 30.0 µm
FIGURE 9.12
(a) Pulsed laser deposition (PLD) method. (b) Typical glass coating (31% SiO
2
; 26.7% MgO; 31.7% CaO; 10.6%
P
2
O
5
) morphologies on Ti substrates using a KrF laser. Left image shows coating produced at low pressure
(10
-7
bar); right image shows coating produced at high pressure (10
-2
bar). (From Joanni et al.,
Mater. Res.
, 7 (3),
2004. [34].)
bioactivity testing showed no loss in bioactivity as a result of the coating process (see Figure
9.13). Using the technique, they were also able to precisely control glass layer thickness by
reraster scanning the substrates surface.
Sol-Gel Coating/Dipping
The use of sol-gel compositions offers the developer the ability to extend the compositional
range of bioactive glass coatings beyond 60 mol% silica. In addition, sols have the ability to
form films on substrates introduced onto them. Dip-coating technology has proved useful
in creating sol-gel-derived bioactive coatings with good interface mechanical properties,
precise control of microstructure, and composition. Precise control of extraction velocity
of the metallic substrate coupled with sol viscosity is the most important parameter to
manufacture good-quality coatings. Extraction velocities must be less than, or equal to,
the gelling rate of the film to avoid flocculation processes and maximize adhesion to the
substrate.
Gomez and coworkers were able to apply glass coatings with thermal expansion coef-
ficients close to Ti
6
Al
4
V substrates using sol-gel dipping. Their glass compositions (see
Table 9.19) exhibited limited capacity to induce apatite formation in SBF immersion (bio-
activity testing). To improve bioactivity, they applied an additional thin (approximately
50 μm) film of mesoporous silica by spin-coating a sol-gel solution [30]. Improved bio-
activity was observed via apatite formation after 7 days immersion in SBF. In addition,
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