The Challenge
Biaxial planar testing of soft tissues is often required to fully characterize
the inherent anisotropic properties of the tissue or to set-up biaxial
stress-strain states to provide more accurate in vivo simulation. With uniaxial
testing, fibers may realign along the test axis, altering the mechanical
properties of the tissue. In addition, constitutive models cannot be developed
based on uniaxial testing alone.
The gripping technique must be capable of securely holding soft tissues, without
causing damage, and lateral deformations must be unrestricted in order to
ensure homogeneous specimen deformation in the gauge area under biaxial
loading. In addition to this, strain measurement must not damage the tissue or
cause stress concentrations and be able to account for strain in all directions
of loading.
Our Solution
The Instron low-force planar-biaxial soft tissue system was developed to perform
mechanical testing and property analysis of soft planar biomaterials, native
tissues and tissue-engineered scaffolds.
The configurable system consists of four fatigue-rated actuators mounted to an
air-suspended isolation table. The system is capable of running both uniaxial
and biaxial tests to offer ultimate flexibility for soft tissue testing.
The FastTrack™ 8800 digital controller is capable of providing true
planar-biaxial control, giving both translation and deformation control in both
axes. This aids in the ability for highly accurate specimen center-point
control, allowing the use of optical instruments mounted above the specimen.
Such instrumentation includes non-contacting video extensometry for precise
measurements of strain in two dimensions or microscope systems for structural
observations. The exceptional resolution of the controller ensures accuracy
when measuring the extremely low loads associated with many soft tissues.
A simple gripping method based on sutures and pulleys distributes the loading
forces equally around the specimen, allowing simultaneous testing along the x
and y axes. The entire system is easily configured with one of Instron's
temperature-controlled environmental baths, for simulation of physiological
conditions during testing.
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