Biomedical Engineering Reference
In-Depth Information
bioactivity of vitronectin (a protein in serum that mediates osteoblast adhesion)
were responsible for the enhanced adhesion of osteoblasts (an important prerequi-
site for anchorage-dependent cell functions) on nanophase ceramic formulations.
Vitronectin preferentially adsorbed to the small pores in nanophase ceramics (such
as 0.98-nm pore diameters in nanophase titania compacts). Adsorption of vitro-
nectin was 10% greater on nanophase compared to conventional alumina.
162,163
Increased unfolding of vitronectin was observed when this was adsorbed on nano-
phase ceramics compared to conventional ceramics. Unfolding of vitronectin
promoted the availability of specific cell-adhesive epitopes (such as the arginine-
glycine-aspartic acid or RGD sequence) that led to enhanced osteoblast adhesion.
The increased adhesion of bone-forming cells, osteoblast, on nanostructured
materials was reported in 1999
133
using alumina with grain sizes between 49
and 67 nm and titania with grain sizes between 32 and 56 nm. These nanomate-
rials were reported to promote osteoblast adhesion compared with their respec-
tive micrograined materials. Additional studies of these nanstructured ceramics
(such as alumina, titania, and HA) exhibited in vitro osteoblast proliferation.
Their long-term functions as measured by intracellular and ECM protein syn-
thesis such as collagen and alkaline phosphatase, as well as calcium-containing
mineral deposition, were superior on ceramics with less than 100-nm grain or
fiber sizes.
134,135
Two, three, and four times the amount of calcium deposition
was observed on nanostructured materials compared with the conventional HA,
titania, and alumina when osteoblasts were cultured for up to 28 days. In addi-
tion, osteoblast functions such as viable cell adhesion, proliferation, and calcium
deposition were further increased on nanofiber materials compared with nano-
spherical structures of alumina. This was believed to result from the nanofibers
having more closely approximate the shape of HA crystals and collagen fibers
in bone compared with nanospherical geometries. The surface chemistry and/
or crystal structures of the conventional ceramics tested in these reports were
similar to their respective nanophase materials except the degree of nanometer
surface features that was altered.
Nanostructured ceramics also exhibited enhanced bone-resorbing (osteo-
clast) functions. Compared with conventional HA, osteoclast synthesis of tar-
trate-resistant acid phosphatase with subsequent formation of resorption pits on
the nanoparticles showed up to two times greater.
164
Osteoblast- and osteoclast-
coordinated functions are important for the formation and maintenance of healthy
new bone placed adjacent to an orthopedic implant. Thus, promoted functions of
osteoblasts combined with enhanced functions of osteoclasts could lead to trans-
formation of bones formed at implant surfaces composed of nanosized ceram-
ics.
112
A few in vivo studies have demonstrated enhanced new bone formation on
metals surfaces with nanomaterials compared with conventional HA implanted in
rats.
165
Enhanced new bone formation was shown on nanosized HA-coated tanta-
lum compared with microsized HA-coated tantalum and the noncoated tantalum
as seen on
Figure 6.5
.
112
These results are very promising for the translation of
data showing greater bone growth on nanomaterials from in vitro to in vivo.
