Biomedical Engineering Reference
In-Depth Information
increasing nanotube size. It is expected that the surface area to be 3 times higher on the
100nm diameter nanotubes compared to the 30nm diameter nanotubes, respectively.
Additionally, the contact angle describing the wettability of the surface is enhanced, more
hydrophilic, on the nanotube surfaces (showing contact angles between 4-11°), which can
been advantageous for enhancing protein adsorption and cell adhesion.
3.1 Protein adhesion properties based on pore size
Cells respond to the amount and area of proteins that are available for binding. In fact, cells
do not see a naked material,
in vivo
or in
in vitro
culture. At all times, the material is
conditioned by the components of the fluid in which the material is immersed, whether it is
serum, saliva, cervicular fluid or cell culture media. As the cell begins to adhere and spread
on the nanotubes, there will be a dissimilar protein density and extra cellular configuration
based on the nanotube diameter. The behaviour of protein adsorption on the nanotube
surfaces are shown in Figure 3. On the 30nm diameter nanotubes there is a large number
and thorough distribution of protein nanoparticles covering the whole surface of the
nanotubes after just 2 hours of incubation in culture media. However, proteins on 100 nm
TiO
2
nanotubes can only adhered sparsely at the top wall surface owing to the presence of
large empty nanotube pore spaces. This inherent protein adsorption property of the
nanotubes based on poresize is hypothesized to influence cell shape and fate. It is shown in
the next sections that the changes in poresize even in such a small range of dimensions (30-
100nm) will have huge impacts on downstream cell morphology and behavior.
Fig. 3. SEM micrographs of flat Ti and 30, 50, 70, 100nm diameter TiO
2
nanotube surfaces
after 2 hours of culture showing protein adsorption from media.
4. Osteo-chondral applications of TiO
2
nanotube constructs
Artificial cartilage prepared from cultured chondrocytes offers promise as a treatment for
cartilage defects (Fedewa et al. 1998), but connecting this artificial soft tissue to bone in the
attempts to restore the defected cartilage is difficult. One strategy employed in this section is
to develop a dually functional substrate that supports the growth and attachment of
cartilage tissue on one extremity and encourages osseointegration, a direct structural and
functional connection to living bone, on the other. This substrate should be an engineered
interface between artificial cartilage and native bone (Zhang, Ma, and Francis 2002).
In recent studies, Ti has emerged as a candidate material in cartilage tissue formation as
well. It has been demonstrated that a micrometer porous substrate of Ti-6Al-4V provided
