Sol–Gel Derived Hydroxyapatite Coatings on Metallic Implants: Characterization, In Vitro and In Vivo Analysis - Biological and Biomedical Coatings - page 11

1

1

3

1

(a) (b) (c)

2

FIGURE 1.3
O1s spectra (XPS) of HA coatings prepared by different methods ([a] sol-gel coating; [b] sputtered coating;
[c] plasma-sprayed coating). Peak 1 is the characteristic O1s peak in HA structure with a binding energy of
531.4eV; peak 2 is attributed to the O1s in adsorbed water; peak 3 is the O1s coming from TiO 2 . (From Massaro
et al., Journal of Biomedical Materials Research , 58, 6, 651-657, 2001. With permission.)

attributed to the O1s in adsorbed water, whereas peak 3 is the O1s coming from TiO 2 . As
such, according to the binding energy of a specified element, it is quite easy to find out
what kind of phase/compound of this element is in. Table 1.4 summarizes the binding
energy levels of core elements in some calcium-containing salts. Importantly, based on the
XPS analysis (especially the narrow scan screening), the determination of trace elements
in the coating is critical for the investigation and evaluation of new biomaterials (Ka č iulis
et al. 1999).
Surface chemistry and composition can also be analyzed by FTIR. The FTIR technique is
rapid and nondestructive, requires no vacuum, and is applicable to samples of any dimen-
sion and even to those with curvature (Kazarian et al. 2004). The chemically specific infor-
mation contained in the unique “fingerprint” region of the IR spectrum allows one to
distinguish different chemical groups and even different materials. In HA, compound
groupings, such as hydroxyl bands (OH groups), carbonate bands (CO 3 groups), and phos-
phate bands (PO 4 groups), are usually quantified by FTIR (Stoch et al. 2005; Vijayalakshmi,
Prabakaran, and Rajeswari 2008). Crystalline HA generates two characteristic OH bands
at about 3570 and 630 cm −1 (Weng and Baptista 1999; Stoch et al. 2000). Sometimes they are
absent in FTIR spectra, and some authors attribute this missing OH modes to a perturba-
tion of hydroxyl stretching and bending modes on the apatite surface by the hydrogen

TABLE 1.4
XPS Binding Energy Values of Main Elements in Some Calcium-Containing Salts

BindingEnergy(eV)

Phase Ca 2p 1/2 Ca 2p 3/2 P 2p O 1s

HA 351.0-351.2 347.2-347.5 133.3-133.5 531.3-531.6
α -TCP a 350.7 347.2 133.3 531.0
β -TCP a 350.6 347.0 133.1 530.9
ACP a 350.6 347.1 133.1 531.1
CaCO 3 b 350.1 346.5 − 533.9 (O I )
535.6 (O II )
Source: Amrah-Bouali et al., Biomaterials , 15, 4, 269-272, 1994; Lu et al., Anal. Chem ., 72, 13, 2886-2894, 2000;
Chusuei, C.C., Anal. Chem ., 71, 1, 149-153, 1999; Yan et al., Biomaterials , 24, 15, 2585-2592, 2003; Battistoni
et al., Surf. Interface Anal ., 29, 11, 773-781, 2000. With permission.
a Peak positions are calibrated by setting the adventitious C1s to 284.7eV.
b Powder form in calcite phase.