Biomedical Engineering Reference
In-Depth Information
sites for protein aggregation leading to pillar formation. Collectively, the evidence demonstrates that
even subtle changes in the nanotopography can lead to dramatic alteration in the protein deposition
pattern. The immediate substrate that cells interact with is the adsorbed proteins rather than the primi-
tive nanotopographies. The notably uneven protein deposition will change the nanotopography and
make the ultimate topographical cues exposed to cells to be quite different from the primitive nano-
topographies, thereby altering the biological performance. The uneven protein distribution con-
sequently leads to compromised cell focal adhesion and following functions including proliferation
and differentiation. It is thus strongly suggested that the protein adsorption pattern should also be
carefully inspected when studying the bioactivity of nanoscale biomaterials.
17.4
In vitro bioactivity of the NTs and in vivo osseointegration
17.4.1
In vitro bioactivity of the NTs
NTs can foster the growth of nanostructured hydroxyapatite. Oh et al.
[8]
have treated the NTs with
NaOH solution to investigate their bioactivity. NTs induce the growth of extremely fine-scale (
B
8nm
feature) nanofibers of bioactive sodium titanate on the top edge of the
15 nm thick NT wall. After
immersion in a SBF, the nanoscale sodium titanate can induce the nucleation and growth of nanodi-
mensioned HA phase. The kinetics of HA formation can be significantly accelerated by the presence
of the NTs. Pittrof et al.
[9]
have developed micropatterned NT layers surrounded by compact oxide
via an optimized process. By immersing such patterns in SBF, selective and dense apatite deposition
occurs only on the NT surfaces (
Figure 17.6
). These results verify the strong ability of the NTs to
induce apatite deposition. Although there is still debate whether SBF can predict the bioactivity of
biomaterials
[36]
, the strong ability of the NTs to foster nanostructured hydroxyapatite deposition to
a certain degree demonstrates their bone formation favoring properties.
B
(A)
(B)
Apatite
Apatite
Apatite
FIGURE 17.6
Patterned samples after immersion in 1.5
SBF. (A and B) Field emission scanning electron microscopy
(FE-SEM) micrographs showing selective apatite nucleation exclusively on nanotube regions.
Reprinted with permission from Ref.
[9]
.
3
