Biomedical Engineering Reference
In-Depth Information
hybrid created by sandblasting and alkali and heat treatment. Compared with
the non-microroughened surface, the microroughened surface accelerated
the establishment of implant biomechanical fixation at the early healing stage
but did not increase the implant fixation at the late healing stage.
157
The use
of nanopolymorphic features on the microroughened surface further increased
implant fixation throughout the healing time. The percentage of BIC increased
four- to fivefold using microroughened surfaces that was further increased by
more than twofold throughout the healing period. Using alkali- and heat-treated
nanopolymorphic surface, critical parameters that were necessary to process
bone-implant integration for which nanofeatures have specific and substantial
roles were identified. Nanofeature-enhanced osteoconductivity, which resulted in
both the acceleration and elevation of bone-implant integration was demonstrated.
The in vivo response of nanoscale titanium implants in terms of nitric oxide
scavenging and fibrotic capsule formation was studied.
158
Titanium dioxide
(TiO
2
) nanotubes with 100-nm diameters fabricated by electrochemical anodiza-
tion with TiO
2
control surfaces showed significantly lower nitric oxide, suggest-
ing that nanotubes break down nitric oxide. The soft tissue response in vivo TiO
2
nanotube and TiO
2
control implants were placed in rat abdominal wall for 1 and
6 weeks showed a reduced fibrotic capsule thickness for the nanotube surfaces
for both time points. In addition, lower nitric oxide activity, measured as the
presence of nitrotyrosine (P < 0.05), was observed on the nanotube surface after
1week. The differences observed may be attributed to the catalytic properties of
TiO
2
that are increased by the nanotube structure. These results give insight for
the interaction between titanium implants in soft tissue as well as bone tissue
that provide a mechanism for the improvement of future clinical implants.
6.3.1.3 Ceramic Nanomaterials
Another interesting material that can serve as implant is ceramic that are known for
their excellent biocompatibility and high resistance to wear. Ceramics find use in
a wide variety of clinical applications such as in orthopedics for femoral head and
hip replacements.
159
Compared with titanium, its high degree of brittleness that is
due to the molecular covalent-ionic binding structure in ceramics prevents plastic
deformation before failure. However, ceramics suffer from microstructural flaws
that cause poor resistance to stress.
160
For applications as dental implants, ceramic
implants that are yttrium-stabilized tetragonal zirconia polycrystal ceramics (PSZ)
has rekindled interest in its application as implant materials. Compared with alu-
minum oxide ceramics, PSZ has a higher fracture resistance and flexural strength
making it less sensitive to stress concentrations. This property is mostly due to the
toughening transformation changing a metastable tetragonal grain structure into a
monoclinic structure at room temperature.
161
This simultaneous 3% expansion in
volume prevents the progression of a crack or flaw in the ceramic.
160
Webster et al.
162,163
have focused on the mechanisms of enhanced cel-
lular activity (such as osteoblast, chondrocyte, etc.) on nanophase materials.
Mechanism-based studies exhibited that the concentration, conformation, and
