Biomedical Engineering Reference
In-Depth Information
composed of calcium hydroxide and calcium carbonate. This is because after calcium has been
deposited onto the titanium surface, it reacts with ambient water and carbon dioxide upon expo-
sure to air to form calcium hydroxide and calcium carbonate. Apatite can be observed on the
surface of the Ca ion-implanted titanium at 10 kV of bias voltage after soaking in an SBF for
28 days, as shown in Figure 19.21.
Calcium is a very active metal that can be oxidized easily in air to form calcium oxide. In the
experiments, a tungsten fi lament was employed to heat the calcium powders to produce the dis-
charge current and calcium ions were plasma implanted by applying a pulsed high voltage to the
titanium samples. During the off-cycle, calcium was deposited onto the sample surface. After the
samples were taken out of the vacuum chamber, the surface calcium reacted immediately with oxy-
gen in air to form calcium oxide (CaO), followed by adsorption of H
2
O and CO
2
to form Ca(OH)
2
and CaCO
3
. The process is schematically illustrated in Figure 19.22.
While in the SBF, calcium ions are released gradually from the sample surface into the SBF
causing supersaturation of calcium ions in the body fl uid in the vicinity of the surface. Hanawa has
postulated that the calcium ion-implanted titanium surface is more positively charged due to the
dissociation of hydroxyl radicals [83].
FIGURE 19.21
Surface views of the Ca ion-implanted titanium at a bias voltage of 10 kV soaked in a
simulated body fl uid for 28 days.
Calcium hydroxide
Calcium titanate
Calcium oxide
Calcium titanate
Titanium oxide
Ca IIIP-D
In air
Titanium
Titanium
Titanium
FIGURE 19.22
Schematic diagram of the surface reaction (cross-section of the Ca PIIID sample shown).
(From Liu, X.Y. et al.,
Surf. Coating Tech.
, 191, 43, 2005. With permission.)
