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for hard tissues such as bone or dental
enamel, using an extensometer to mea-
sure strain is required. Further, for both
hard and soft tissues, it is considered
best practice to use an extensometer to
measure properties such as modulus.
During a tensile or compression test, a
force is applied to a material causing
deformation. For hard tissues with high
stiffness, the material will deflect under
load and some test system deflection
(compliance) will also occur. To avoid
having system compliance factored
into the specimen’s strain measure-
ment, using an extensometer is recom-
mended. Because soft biomaterials are
delicate and fragile, a noncontacting
extensometer such as a laser or video
model is required.
SUMMARY
Mechanical characterization of
both natural and engineered biomate-
rials is done through a combination of
static and fatigue testing to understand
both bulk and lifetime material proper-
ties. Given the natural variability of bio-
materials, it is critical that mechanical
testing design reduces test variables
such as low force measurement, speci-
men gripping, and strainmeasurement.
While data sheets with mechanical test
specifications are available for materi-
als such as polymers, elastomers, and
metals, biomaterial mechanical prop-
erties are still largely unknown or only
published academically. As scientists
and engineers continue to develop
and investigate replacement tissues
for patient disease, injury, and aging,
proper mechanical characterization of
biological materials is critical.
~AM&P
For more information:
Elayne Gor-
donov is biomedical assistant market
manager, Instron, 825 University Ave.,
Norwood, MA 02062-2643, 800.877.6674,
www.instron.us.
Tensile testing of hydrogels using a video extensometer.