Biomedical Engineering Reference
In-Depth Information
The ideal situation is to maintain a pH between 3 and 4, because
it maintains an adequate pH to carry out the gastric function. The pH
higher than 5 produces a gastric disturbance in the patient and the
enzymatic activity of the pepsin is drastically diminished [17, 36].
Linares
et al
. did not found excess salts on the carbon surface.
A novel adherent, continuous, nanocrystalline hydroxyapatite/
diamondlike carbon bilayer ilm was produced using pulsed laser
deposition [46]. The diamondlike carbon (DLC) interlayer between
the hydoxyapatite surface and the substrate improves hydroxyapatite
ilm adhesion and prevents corrosion or third body wear in the
bulk implant material [46]. The term diamondlike carbon refers
to amorphous carbon thin ilms that contain some sp
3
-hybridized
atoms. These materials have atomic number densities greater than
3.19 g
⋅
atom/cm
3
, and exhibit densities closer to that of diamond
(3.51 g/cm
3
) than that of graphite (2.26 g/cm
3
) [47]. Amorphous
hard carbon thin ilms demonstrate properties intermediate between
those of graphite and those of diamond. These ilms contain a mixture
of sp
3
-hybridized carbon atoms and sp
2
-hybridized carbon atoms.
Within the amorphous carbon matrix micro- or nanocrystalline
graphite domains may be observed [47].
Processing of diamondlike carbon thin ilms is followed by
sputtering, bombardment with energetic species, electrostatic
acceleration of carbon ions, arc discharge, or laser ablation [47].
Diamondlike carbon thin ilms have shown excellent compatibility
to human cells [4, 38, 39, 47, 56]. The osteoblast cells exposed to DLC
coatings did not demonstrate any change in generation of alkaline
phosphatase, type I collagen, or osteocalcin [5] and neuronal growth
occurs on DLC layer [23]. The TEM micrograph shown in Fig. 10.4
demonstrates several layers within the functionally gradient ilm
structure [47]. These ilms exhibit signiicantly higher hardness
values than the underlying Ti-6Al-4V alloy.
The titanium carbide/titanium carbonitride/titanium nitride
region serves as a functionally gradient zone between the Ti-6Al-
4V substrate and the diamondlike carbon layer. The silver regions
within the functionally gradient diamondlike carbon-silver layer
provide ductility to the ilm through cracking. Narayanan [47]
envisaged applications for multilayer hydroxyapatite/diamondlike
carbon ilms, in orthopedic and dental implants.
