Hydrothermal Crystallization with Microstructural Self-Healing Effect on Mechanical and Failure Behaviors of Plasma-Sprayed Hydroxyapatite Coatings - Biological and Biomedical Coatings: Processing and Characterization - page 262

H 2 O peak at BE = 533.2 eV [171,176-178]. The adsorbed H 2 O represents that the surface
of the HT-HACs is possibly affected by the surrounding moisture in the saturated steam
atmosphere in the autoclave, and H 2 O molecules can be physically adsorbed on the HACs.
However, the surface residual adsorbed H 2 O is absent because the surface adsorbed H 2 O is
diminished with the reduction of hydroxyl-deficient state during hydrothermal treatment
[171], especially under a higher saturated steam-pressure atmosphere. In Figure 6.18c, the
O 1s spectra obtained at the HT-HACs/Ti substrate interface are fit with four peaks: the
above-mentioned PO, POH peaks of HA, the Ti-O peak at 529.6 eV, and the Ti-OH peak at
532.5 eV. The Ti-O peak can be attributed to the surface oxide ion of Ti substrate, and the
peak at ΔBE about 3.0 eV from Ti-O peak can be assigned to the chemisorbed OH − groups
of Ti-OH [177-179]. Considering that the rapid solidifi cation of molten HA droplets dur- ]. Considering that the rapid solidiication of molten HA droplets dur-

ing plasma spraying induces the formation of ACP at the HAC/Ti substrate interface, the
analysis results represent that the hydrothermal treatment promotes the interfacial crys-
tallization through the chemical bonding of OH − groups. The biocompatibility tests in
vitro have demonstrated that crystalline HA has a considerably lower dissolution rate and
the presence of Ti-OH bonding can further enhance the bioactive properties of the HA
coating by promoting the osteointegration process [178,180].
In addition, Yang et al. indicated that the hydrothermally crystallized HACs also show
better in vivo biological responses through examinations with the Chinese coin implant

177-179]. Considering that the rapid solidifi cation of molten HA droplets dur- -179]. Considering that the rapid solidifi cation of molten HA droplets dur- 179]. Considering that the rapid solidifi cation of molten HA droplets dur-

(a)

Bone marrow

New bone

HAC

Ti-6Al-4V

OB

OB

(b) (c)

NB

NB

C

C

T

T

0.5 mm 0.5 mm

FIGURE 6.19
(a) Schematic illustration of new bone healing index (NBHI) and apposition index (AI). SEM/BEI of histological
section at surgical defect region for 12 weeks postimplantation: (b) plasma-sprayed HACs and (c) HT-HACs.
New bone is repaired within surgical defect regions of two HACs. Osseointegration is found at both bone/
plasma-sprayed HACs and bone/HT-HACs interfaces. T, Ti-6Al-4V; C, coating; NB, new bone; OB, old bone.
(From Yang et al., J. Biomed. Mater. Res. , 83A, 263-271, 2007. With permission.)