Biomedical Engineering Reference
In-Depth Information
due to surgery rather than due to the implant. In principle, the method would be
suitable to detect bacterial infection; however, the fluorescence signal was highly
variable in independent experiments. Visualization of inflammatory protease activ-
ity also showed increased signal intensity after implantations. However, the signal
was delocalized and could not be assigned to individual implants. For our purposes,
this method did not appear suitable to distinguish inflammatory potential of different
implant materials. The approach to monitor cell growth stimulatory signals has been
used to detect tumors and is also expected to be associated with cell proliferation
during wound healing processes [
33
]. Autotaxin activity was observed to increase
with time at the site of implants associated with bacteria. Unfortunately the signals
were not sufficiently localized to allow any reliable assignment to individual im-
plants. In addition, the signal was barely detectable due to the high background [
34
].
Therefore, it was not possible to quantify the inflammatory potential of individual
implants using this strategy.
Strategies for visualizing enzymatic activities or presence of reactive molecules
using fluorescent probes generally suffer from high background due to autofluo-
rescence of tissue as well as background fluorescence of the probe. The transgenic
mouse model employed in this study uses bioluminescence to visualize the induction
of a IFN-
as an inflammation related cytokine. The high signal to background ratio
facilitated the quantification and a distinct difference between bacteria coated and
non-inflammatory titanium implants was observed. No interferon response was ob-
served with any other clinically used implant material (data not shown). This assay
could therefore be used to investigate bacterial infections on implant materials and
to determine the efficacy of antibacterial implant coatings.
The major advantage of in vivo imaging is that each animal can serve to include
internal controls by using appropriatematerials implanted in the same animal, thereby
improving the reproducibility by avoiding even subtle differences in the handling
and animal to animal variability [
35
]. Both, fluorescent as well as bioluminescent
strategies could be used.
In conclusion, various techniques were investigated to evaluate the inflammatory
potential of prospective implant materials. Compared to the fluorescent detection
methods investigated here, a luminescent transgenic mouse model appeared most
promising to distinguish biocompatible and immune stimulatory implants.
β
Acknowledgments
This research was funded in part by Collaborative Research Centre grant
SFB599 by the Deutsche Forschungsgemeinschaft. We thank Dr. Thomas Ebel from Helmholtz
Centre Geesthacht, Germany for providing porous titanium discs. B.R. was funded by Helmholtz
graduate school and M.I.R was supported by a joint grant of DAAD (German Academic Exchange
Service), Germany and Higher Education Commission of Pakistan.
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