Testing and introduction of new materials - Orthopaedic Biomaterials in Research and Practice - page 384

4. Evaluation concentrates on examination of local host response and
neglects study of systemic or remote site effects unless gross mor-
bidity or mortality occurs.

5. It does not provide a comprehensive assessment of the systemic
toxicity, immune response, carcinogenicity, teratogenicity, or
mutagenicity of the material, which is covered by other standards.

6. This only applies to materials that are expected to reside in bone
or soft tissue in excess of 30 days and will remain unabsorbed.

It is to be hoped that improved test procedures will come into use for
evaluation of chronic (>30 days) biomaterials. There has been increased
interest in recent years in the use of active prostheses, scaled for the test
animal, to evaluate the performance of new materials, especially surface
coatings adapted for fixation by tissue adhesion or ingrowth.

Tools for design: material testing

When seeking to introduce a new biomaterial, there are numerous stan-
dards that provide guidance to the design team to consider. The ASTM
has published standards that cover various test methods including cor-
rosion, wear, fatigue, degradation, aging, and strength. These methods
utilize not only materials testing equipment but also microscopy and
other chemical and physical characterization tools. Optical microscopy
is one of the most readily available laboratory tools and is utilized for
the close-up examination of an object surface. In particular, using light
and a system of lenses, it allows the magnification of small features
following testing of a particular material. One example would be the
examination of witness marks on knee arthroplasty components whose
non-articulating surfaces were contacting owing to impingement.
It may also be important to understand the chemical and physical
properties of a material and how it may change in anticipated environ-
ments. Information that may be useful includes knowing the purity and
constituents of a material, the impact of its temperature in a certain envi-
ronment, its degradation state, and the condition of its surface.

Fourier transform
infrared spectros-
copy

Fourier transform infrared (FTIR) spectroscopy is a technique used
to identify the constituents of a material through examination of how
well the material absorbs and transmits infrared energy (wavelength
longer than visible light) of differing wavelengths. After directing an
input infrared spectrum onto a sample, the frequencies of the vibrations
between the atomic bonds in the sample alter the spectrum output to a
detector. On the basis of the resulting spectrum, FTIR can identify an
unknown material, the amount of each constituent of a sample, or the
quality of a substance. It has been described as exposing the unique “fin-
gerprint” of a given sample. FTIR can be used to characterize the degra-
dation of polymers caused by sterilization and aging (oxidation index) or
to determine a material's potential to oxidize (hydroperoxide index). An
indication of the degree of molecular cross-linking in a material, which