Biomedical Engineering Reference
In-Depth Information
material if the mechanism of biodegradation involves bioerosion, that is, enzy-
matic or hydrolytic cleavage at the surface. Visual examination of the surface with
various microscopic techniques can also give information on the biodegradation
process [123-126]. Likewise, chemical and/or physical changes in the polymer may
be followed by (combinations of) specifi c techniques such as infrared [10, 127] or
UV spectroscopy [84, 128], nuclear magnetic resonance measurements [122-129],
X-ray diffractometry [130, 131], and differential scanning calorimetry [132, 133].
11.5.6.3
Drawbacks
An inherent drawback in the use of mechanical properties, weight loss, molecular
weights, or any other property which relies on the macromolecular nature of the
substrate is that in spite of their sensitivity, these can only address the early stages
of the biodegradation process. Furthermore, these parameters can give no infor-
mation on the extent of mineralization. Especially in material blends or copoly-
mers, the hydrolysis of one component can cause signifi cant disintegration (and
thus loss of weight and tensile properties), whereas other components may persist
in the environment, even in disintegrated form [13]. Blends of starch, poly(3-
hydroxybutyrate) or poly(
ε
- caprolactone) with polyolefi ns are examples of such
systems [11, 43, 134] .
11.5.7
Natural Environments, Field Trials
Exposures in natural environments provide the best true measure of the environ-
mental fate of a polymer, because these tests include a diversity of organisms and
achieve a desirable natural closeness of fi t between the substrate, microbial agent,
and the environment. However, the results of that exposure are only relevant to
the specifi c environment studied, which is likely to differ substantially from many
other environments. An additional problem is the timescale for this method, since
the degradation process, depending on the environment, may be very slow (months
to years) [23]. Moreover, little information on the degradation process can be
gained other than the real time required for weight loss or total disintegration.
Nevertheless, fi eld trials in natural environments are still used to extrapolate
results acquired in laboratory tests to biodegradation behavior under realistic
outdoor conditions [123, 135, 136] .
11.6
Conclusions
The overview presented above makes clear that there is no such thing as a single
optimal method for determining biodegradation of polymeric materials. First
of all, biodegradation of a material is not only determined by the chemical com-
position and corresponding physical properties; the degradation environment in
which the material is exposed also affects the rate and degree of biodegradation.
