Biomedical Engineering Reference
In-Depth Information
(B)
(A)
500 nm
100 nm
100 nm
1
µ
m
200 nm
100 nm
500 nm
(C)
(D)
100 nm
200 nm
300 nm
10
µ
m
300 nm
1
µ
m
10
µ
m
FIGURE 7.2
Scanning electron microscopy (SEM) images showing TiO
2
nanotube layers grown by different anodization
processes of Ti. (A) Typical morphology obtained in acidic fluoride or HF electrolytes, (B) glycerol/fluoride
electrolytes, (C) ethylene glycol/fluoride electrolytes. The insets show top views (open tubes), bottom
views (closed ends), and side walls in detail. (D) Tubes grown by a different approach: rapid breakdown
anodization (RBA); these tubes grow in disordered bundles within seconds at comparably high anodic
potentials. The upper inset in (D) shows a side view of the layer, the lower inset shows a low magnification
of the surface
[11]
.
when compared with clinically used hydroxy apatite-β tricalcium phosphate (HA-βTCP) inserts
[35]
.
It was shown that the presence of chemically modified TiO
2
nanotubes have significantly acceler-
ated the kinetics of hydroxyapatite growth by 7 times. Chemical modification of TiO
2
nanotubes with
sodium hydroxide (NaOH) has resulted in surface with bioactive nanoscale sodium titanate
[36]
,
which can enhance osteogenesis (
Figure. 7.4
). A recent study on osteoblast adhesion on TiO
2
nano-
tubes (30-100 nm diameter) concluded that large diameter nanotubes, in the approximately 100 nm
regime induced extremely elongated cellular shapes, which resulted in substantially enhanced upregu-
lation of alkaline phosphatase activity, suggesting greater bone-forming ability than nanotubes with
smaller diameters (30 nm)
[37]
. These nanotubes stimulate calcium phosphate crystal formation and
deposition when exposed to 20 cycles of alternating immersion in saturated Ca(OH)
2
and 0.02 M
(NH
4
)
2
HPO
4
(
Figure. 7.5
). Such approaches prove that calcium phosphate coatings can be fabricated