Bioresorption and Degradation of Biomaterials - Tissue Engineering: Cell-Surface Interactions for Tissue Culture - page 327

3.3 In Vivo Tests of Biomaterial Degradation
Even cell-based in vitro tests cannot completely model the in vivo situation and
therefore in vivo biomaterial degradation is also monitored. Different methods are
used depending on the type of material. The most widely applied methodology so
far has been histology combined with different analysis technologies. This, how-
ever, requires explantation of the tissue in which the material was embedded and
can therefore only be used pre-clinically. Assessment of biodegradation and
bioresorption has been reported in terms of changes in macro-porosity, density,
changes in pore and grain diameters and average crystal size with time from the
surface and the core of implant materials as observed by scanning (SEM) and
transmission (TEM) electron microscopy [ 54 , 99 ]. For more accurate and specific
analysis, energy-dispersive X-ray analysis (EDX) and Fourier transform infrared
(FT-IR) spectrophotometry are employed. Elemental analysis can be carried out by
EDX, which is connected to SEM. Chemical analysis of composites can be carried
out by FT-IR spectrophotometry [ 100 ]. With the application of synchrotron-
radiation-based microtomography (SRlCT) in attenuation mode, not only can the
amount of biomaterial degradation be monitored in 3D, but also the spatial dis-
tribution of alloying elements during in vivo corrosion [ 101 , 102 ].
For nondestructive in vivo analysis of degradation of radiodense biomaterials,
X-ray lCT systems can be used to determine biodegradation, bioresorption, and
the extent of reaction of the surrounding tissue [ 103 ]. X-ray lCT has a spatial
resolution in the micrometer range depending on the area of interest and is
commonly used in small animal testing. X-ray lCT or magnetic resonance
imaging (MRI) systems combined with positron emission tomography (PET) or
single photon emission computed tomography (SPECT) scanners can be used to
monitor the functional processes of biologically active molecules in the body by
injecting a short-lived radioactive isotope tracer [ 104 ]. Non-irradiation techniques
such as micro MRI (lMRI) and functional MRI (fMRI) also have resolutions in
the micrometer scale and can therefore be used for analysis of the degradation of
non-radiodense biomaterials [ 105 ].
4 Conclusions and Outlook
The human body is a composite structure, completely constructed of biodegrad-
able materials, and can last—with good maintenance—for more than 100 years.
It achieves this goal by constantly actively repairing skin, bones, gut, liver and
many other tissues. This repair process includes bioresorption of the old structure
and replacement of it with new tissue. As this is the result of millions of years of
evolution, it seems only sensible to adapt this method for the use of biomaterials
too. In recent years there has been huge progress in this area. Apart from the
materials mentioned above, bionic nano-methods now allow the production of