Biomedical Engineering Reference
In-Depth Information
R
880 C
°
R
R
R
R
R
R
R
680°C
R
R
R
R
R
R R R
R
R
R
620°C
R
R
R
T
R R
R
T
R
R
R
T
T
T
A
R
580°C
T
T
R
A
R
R
R
R
T
R
R
R
T
R
T
T
480°C
T
T
T
R
T
A
R
R
T
A
T
T
430°C
T
T
T
A
T
R
T
A
T
T T
280°C
T
A
T
T
T
T
T
A
T T
230°C
T
T
T
T
T
T
80
20
30
40
50
60
70
2
θ
(deg)
FIGURE 5.11
XRD patterns of the nanotube annealed at temperature ranging from 230°C to 880°C in oxygen ambient for 3 h.
A, anatase; R, rutile; T, titanium. (From Varghese et al.,
J. Mater. Res.
, 18, 156-165, 2003. With permission.)
near 430°C, peaks from the rutile phase emerge from the XRD spectrum. Above this tem-
perature, the rutile (110) peak becomes more intense while the anatase (101) peak is weaker.
Complete transformation to rutile takes place in the temperature range from 620°C to
680°C (Varghese et al. 2003). Annealing at a high temperature damages the nanotubes.
Yang and coworkers had conducted crystallization of 4.2-μm long nanotubes with a pore
size of about 80 nm at 300°C to 800°C. The length and average diameter of the nanotube
are not changed substantially after calcinations at up to 500°
C. However, the nanotube
length decreases to 3 μm after treatment at 550°C. After calcination at higher temperature
of 600°C and 700°C, the length diminishes to 2.8 and 1.5 μm, respectively. At 700°C, small
protrusions occur through the nanotubes leading to cracking. The nanotube structure
completely collapses when calcinated at 800°C (Yang et al. 2008a).
Biological Performance and Applications
Cell Response to Titania Nanotubes
The geometry of titania nanotubes that can be tailored influences the cell response. Popat
and coworkers have carried out systematical investigation on the cell response for engi-
neered titania nanotube arrays. A nanotube array about 80 nm in diameter and 500 nm
in length is used. Progressively enhanced cell proliferation and ALP activity are observed
compared to pure titanium. No adverse immune response occurs under in vivo conditions
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