Soft Tissues: Uniaxial

The Challenge

Testing of human tissues such as ligaments, tendons, spinal cord and esophagus is essential to the characterization of their behavior in vivo. Testing is performed to determine material properties used to set design specifications for bio-engineered replacement tissues and determine expected values in surgical simulation and modeling tools. In order to accurately replicate tissue behavior during testing, it is essential that the physiological conditions are maintained.

There are many challenges associated with measuring strain in these types of specimens. First, a traditional clip-on extensometer can usually not be attached because the weight of the device may affect load readings. The knife-edges may permanently damage the specimen and attachment of the device to soft and compliant specimens is often difficult. Finally, biomedical testing methodologies often require that these specimens be evaluated in a temperature-controlled bath, requiring submersion of the extensometer, a task that is usually not possible.

Our Solution

Within the Biopuls™ range there is a wide choice of high and low-capacity fixtures and environmental baths for tensile and fatigue testing of a variety of tissues. These solutions operate with any Instron test system that provides advanced electronics for precision, reliability and control.

Alignment is less of a concern with soft tissues than with harder materials, but the problems of gripping are much more severe. The gripping solution is often specific to the characteristics of the specimen material and the conditions of the test. The wide variety of Instron options include line contact jaw faces, roughened grip surfaces, interlocking wave profile faces, adhesively bonding of the specimen ends, staples or stitched ends, through to freezer or cryogenic grips.

The BioPuls Bath was specifically designed for use with the Standard Video Extensometer, one of Instron’s most technologically advanced non-contacting strain measurement devices. This combination allows accurate strain measurement in a temperature-controlled fluid environment that is ideal for a wide range of biomedical testing applications. Gage length marking techniques for submersed specimens are usually unique to the application, but previous research has shown that permanent ink, superglue and adhesive putty have proven successful in marking a specimen through failure. Measurement accuracy of the video extensometer with the BioPuls Bath is ±15 µm or ±0.5% of the gage length reading (whichever is greater). On-site extensometer verification is available for axial strain readings.