Biomedical Engineering Reference
In-Depth Information
1995; Sun et al., 2002). The bond between the coating and the bone is a chemical one
and, therefore, much stronger than that between the metal substrate and the coating
(mechanical or physical bonding) (LeGeros et al., 1995). For this reason, separation of the
coating from the substrate (Daculsi et al., 1995) is not a surprising occurrence.
Alternatives to Plasma-Spray Technique of Depositing Calcium Phosphate Coating
In addition to the nonhomogeneous composition of a plasma-sprayed HA coating, the
plasma-spray method cannot provide a complete and uniform coverage for implants of
complex geometry or porosity because it is a line-of-sight method and subject to shadow-
ing. Because of the disadvantages of the plasma-spray technique in depositing calcium
phosphate coatings, several alternative methods of depositing calcium phosphate coatings
have been pursued.
Grit-blasting with calcium phosphate abrasives
. Ti alloy surfaces grit-blasted with apatitic
abrasive showed the presence of apatite in the x-ray diffraction pattern before passiva-
tion with HNO
3
; to some extent, even after passivation, the presence of calcium and phos-
phorus elements was observed in the energy dispersive X-ray spectroscopy (EDS) profiles
(Figure 7.10). Implanted Ti alloy cylinder showed direct contact with the new bone on the
side grit-blasted with apatitic abrasive and fibrous tissue interface on the side grit blasted
with alumina abrasive (Figure 7.11), indicating that grit-blasting with apatitic abrasive may
introduce bioactive property to the implant (LeGeros and LeGeros, 2006).
Precipitation or biomimetic method of depositing calcium phosphate coating
. Calcium phos-
phate deposition by precipitation on porous Co-Cr-beaded surfaces is used in one com-
mercial orthopedic prosthesis (Table 7.2). This coating (Peri-Apatite), identified as apatite
by x-ray diffraction (Figure 7.5), is obtained by precipitation at 80°C from solution contain-
ing calcium and phosphate ions (LeGeros, 1991; Zitelli and Higham, 2002). Nanoapatite
crystals deposited on dual acid-etched Ti alloy (discrete crystalline deposition [DCD]) as
a thin coating on a commercial dental implant demonstrated direct bonding with bone
(Mendes et al., 2007).
(a)
(b)
Ti
Ti
6 weeks
6 weeks
FIGURE 7.11
Microscopic images of Ti alloy rod after implantation. One side (a) of the rod was grit-blasted with apatitic
abrasive, the other (b) with alumina abrasive. Direct bone-bonding was observed with side (a), fibrous tissue
interface between the Ti rod and the new bone was observed with side (b) indicating that grit-blasting with apa-
titic abrasive enhanced osseointegration, whereas grit-blasting with alumina did not. (From LeGeros et al., in
LeGeros, R.Z., LeGeros, J.P. (eds.)
Bioceramics 11
, Worldwide Scientific Publ, Singapore, pp 181-184, 1996; LeGeros
and LeGeros,
Adv. Sci. Technol
., 49, 203-211, 2006. With permission.)
