Biomedical Engineering Reference
In-Depth Information
phosphate (OCP), or monetite (DCPA) (DaSilva et al., 2001; Kumar et al., 1999; Lin et al.,
2003; Narayanan et al., 2008; Shirkanzadeh, 1991).
Adherent OCP coating was obtained on different surfaces (Ti alloy grit-blasted with
apatitic abrasive, arc-deposited, acid-etched, and Co-Cr-beaded surfaces) using pulse-
modulated electrochemical deposition method (Lin et al., 2003; LeGeros et al., 2004). In this
pulse-modulated method, Ti alloy plates were immersed in solution containing calcium
phosphate, pH 5 at 60°C. Voltage is applied causing the plates to be negatively charged,
thus being able to attract the positive ions (Ca
2+
and H
+
) from the solution; the voltage is
discontinued, allowing the now positively charged plates to attract the negative ions (PO
4
3
,
HPO
4
) to react with the Ca
2+
ions, causing the formation of calcium phosphate (in this case,
OCP) on the plates' surfaces. The voltage is alternately applied and discontinued until the
desired calcium phosphate coating thickness is achieved. The crystal size of calcium phos-
phate in the coating can be manipulated by adjusting the current density or the pulse time:
the higher the current, the smaller the crystal size; the greater the pulse time, the larger
the crystal size (Lin et al., 2003). Using this pulse-modulated electrochemical deposition
method, different types of calcium phosphates (e.g., DCPD, DCPA, calcium-deficient apa-
tite, carbonate-substituted apatite, fluoride-substituted apatite, and other substituted apa-
tites or substituted
β
-TCP), in addition to OCP, can be deposited on Ti alloys or other metals
by adjusting the composition, pH, and temperature of the solution (LeGeros, 1991; LeGeros
et al., 2004). Figure 7.13 shows coatings of calcium-deficient apatite, carbonate-substituted
(a)
(b)
(c)
(d)
FIGURE 7.13
Deposition of different calcium phosphates on Ti alloy disks using pulse-modulated electrochemical method.
SEM images: (a) carbonate-substituted apatite; (b) calcium deficient apatite; (c) fluoride-substituted apatite; and
(d) OCP. (From Lin et al.,
J. Biomed. Mater. Res
., 66A, 810-828, 2003. With permission.)
