Biomedical Engineering Reference
In-Depth Information
Interferometry Case Studies
Interferometers have been used to quantify quality of implant laser micromachining
[30]
and implant
material degradation
[31]
and to evaluate the surface properties of commercial implant screws
[32]
.
In this later work of Svanborg et al.
[32]
, different commercial screw-shaped implants with dif-
ferent surface modifications were investigated. Two of these commercial implants tested were
OsseoSpeed™ and Lifecore™. OsseoSpeed implants had a blasted surface and the Lifecore had
a turned surface. The Lifecore surface was found to be less rough on the micrometer and nanom-
eter levels. The surface roughness was examined using a white-light interferometer (MicroXAM™,
Phaseshift, AZ, USA). A 50
objective and a zoom factor of 0.62 were used with a measurement
area of 264
200 μm and the vertical measuring range of 100 μm. The maximal resolution of the
technique was reported as 0.3 μm horizontally and 0.05 nm vertically.
The work of Svanborg et al. showed the use of the three-dimensional roughness parameters (e.g.,
Sa rather than Ra) that allow for better averaging of the roughness of the surface and also the impor-
tance of surface profile data filters. To be able to describe the surface topography, the roughness, the
waviness, and shape must be taken into consideration. The standard filter used to separate roughness
from waviness and shape for digital three-dimensional measurements on a micrometer level is a high-
pass Gaussian filter. A filter size of 50
50 μm was used for evaluation of the micrometer rough-
ness. However, to evaluate the roughness at the nanometer level, the micrometer roughness must be
regarded as waviness and a suitable filter size to eliminate it must be identified. A 1
1 μm high-pass
Gaussian filter was found to be useful for identifying nanometer roughness with respect to height
deviation. A low-pass filter was also applied to show how much of the shape, waviness, and rough-
ness that were removed by the high-pass filter.
Figure 18.4
shows the affects of filter choice for the
OsseoSpeed and less rough Lifecore surfaces.
18.2
MEASUREMENT OF NANOSTRUCTURE INTERNAL GEOMETRIES
18.2.1
Transmission Electron Microscope
TEM is an established characterization technique, which is capable of providing both image mode
and diffraction mode information from a single sample
[33]
. It is regarded as one of the main tech-
niques for nanomaterial characterization, largely due to its high lateral, spatial resolution which is in
the region of 0.08 nm
[34]
. A feature of nanomaterials is that specific properties, e.g., color, can be
related to a particle's size. Agglomeration of nanoparticles or failure to isolate individual nanostruc-
tures is likely to result in anomalous property characterization. Characterizing the elastic or mechani-
cal properties of individual nanoparticle/nanotube/nanofibers is a challenge to many existing testing
and measurement techniques. It is difficult to pick up samples and difficult to clamp samples, in order
to test for tensile strength or creep, for example
[35]
.
18.2.1.1 TEM Case Studies
TEM has shown itself to be capable of meeting such challenges. It is commonly used specifically
for its ability to isolate and examine individual nanoparticles. This approach reduces the potential
for agglomeration which can be a problem with wet-based laser scattering techniques. Nanoparticles
attached to CNTs have been imaged, with remarkable clarity
[36]
. The select area electron diffrac-
tion patterns revealed very clear diffraction rings owing to the polycrystalline nature of the iron oxide
