Biomedical Engineering Reference
In-Depth Information
major accomplishments have been made in the generation of geometrically defined surfaces
with the fabrication of Al and Si nanostructured surfaces. There is rapidly increasing
evidence that the lateral spacing of features on the nanoscale can impact and change cell
behaviour (Boyen et al. 2002; Cavalcanti-Adam et al. 2006; Popat et al. 2006). Therefore, in
order to optimize the lateral spacing of the TiO
2
nanotube system, by changing the geometry
of the nanotubes, four different pore sizes (30, 50 70, and 100nm in diameter) were created
(Figure 2) for examination of cartilage chondrocyte cells, bone osteoblast cells, and osteo-
progenitor mesenchymal stem cells.
Fig. 2. Physical characterization of different size nanotube surfaces. (a) SEM micrographs of
self-aligned TiO
2
nanotubes with different diameters. The images show highly ordered
nanotubes with four different pore sizes between 30-100nm created by controlling the
voltage from 5-20V. (b) Table with the applied voltage parameter, estimated inner pore size
from SEM images, average roughness (Ra) and surface contact angle measurements for Ti
and 30-100nm TiO
2
nanotube surfaces.
In terms of current biologically active implants, enhanced surface roughness is one of the
important factors in providing the proper cues for a positive cell response to implanted
materials. However, much of the research related to the effect of macro and micro-
roughness on cellular responses and tissue formation are inconclusive due to the non-
uniformity of macro and micro-roughness stemming from crude fabrication methods like
polishing, sand blasting, chemical etching and so on. An important aspect of our nanotube
system shown in the SEM images (Figure 2) is that the nano-topography can feature a more
defined, reproducible and reliable roughness than micro and macro-topography for
enhanced bone cell function
in vivo
. Although, the heights of the nanotube walls increase
proportionally to the increasing diameter, there is no evidence of changes in surface
roughness between the different sized nanotubes based on atomic force microscopy (AFM)
data (Figure 2 (b)). As expected, the nanotube surfaces have a slightly higher roughness over
flat Ti, but between the nanotubes, there appears to be no difference. The AFM data was
performed because it is a somewhat standard surface analysis technique as it is useful for
coarser or microscale roughness measurements, say for other convential coatings, but for
the nanotube dimensions it may not always represent the true roughness when the probe tip
radius is not substantially finer than the nanotube dimensions such as in the TiO
2
nanotube
case. The wall thickness, pore diameter, nanotube spacing, etc can be as small as ~10 nm,
while the AFM probe tip diameter can be as large as 30 - 50 nm.
Furthermore, it can be assumed that the surface area on the nano-scale may be affected
based on the various sizes and the surface area probably increases proportionally with
