Innovative extension-inflation-torsion testing machine for Graz University of Technology

The Institute of Biomechanics at Graz University of Technology in Austria focuses on the investigation of the biomechanical behavior and the underlying microstructure of soft biological tissues, mainly cardiovascular tissues. The goal of these investigations is to develop material laws in the realm of continuum mechanics which are able to describe the behavior of the soft tissue. Moreover, with these laws and Finite Element method simulations the Institute of Biomechanics is able to investigate various complex patient-specific boundary-value problems, e.g., balloon angioplasty with stenting, more closely.

For its scientific research activities into tube-like structures the Institute of Biomechanics equipped the laboratory with an innovative extension-inflation-torsion testing machine by ZwickRoell´s subsidiary company Messphysik for both quasi-static and highly dynamic loading regimes. As most of the tissues in the body are subjected to multi-axial loads, the goal is always to be as close as possible to the in vivo multiaxial loading state, which demands sophisticated equipment.

The innovative testing machine from Messphysik enables the Institute of Biomechanics to apply an axial force (extension), an internal pressure (inflation) and a rotational deformation (torsion) to the tissues - all at the same time. The tissues under test are located in a physiological solution bath. Through symmetrically moving crossheads the specimen center always stays in the same horizontal position. Due to the sensitivity of the structures being tested it is necessary to measure the extensions without influencing the specimen under test. Messphysik developed a solution consisting of a combination of the non-contacting laserXtens and videoXtens systems. videoXtens measures circumferential and axial strains at the same time, while laserXtens measures the torque applied to the tissues.

The equipment of the laboratory belonging to the Institute of Biomechanics includes biaxial tensile and triaxial shear testing systems. All the afore-mentioned systems were designed and built tin collaboration with Messphysik. The main tests are uniaxial and biaxial extension tests on biological soft tissues, followed by triaxial shear tests on orthotropic thick tissues (myocardium) and extension-inflation-torsion tests on tube-like structures such as arteries, esophagi, and tracheae.

"We have long-standing experience with Messphysik and the company is located close to Graz, which simplifies handling of system issues and maintenance and prototype design," explains Dr. Gerhard Sommer, research engineer at the Institute of Biomechanics at Graz University of Technology.