Auckland Bioengineering Institute

Shear testing rig


This novel tri-axial materials testing device has been developed by the Auckland Bioengineering Institute for the testing of highly deformable soft biological tissues using a shear deformation.

The device consists of two main components; a stationary upper platform and a lower platform that contains a 3 dimensional translation stage. The principle of operation is that the tissue samples are affixed to both the upper and lower platforms using a thin layer of superglue then bathed in an appropriate physiological solution. The lower platform is moved relative to the fixed upper platform using the tri-axial translation stage.

The device incorporates an array of force transducers that allows the three orthogonal forces to be recorded. The X and Y force transducers are based on the deflection of fixed beams. The upper platform is connected to the centre of an inner brass ring via stainless steel beams which in turn is connected to an outer brass ring again using stainless steel beams. Strain gauges mounted on the inner beams measure the X force component whilst the outer beams have gauges attached to measure the Y force. The remaining vertical Z force is measured using a load cell mounted on the lower platform.

Motor control and data acquisition is achieved using software written in the LabView programming environment on a windows based personal computer. Motor control of the tri-axial translation stage is achieved using a dedicated National Instruments PCI-7344 motor control card utilising a PID control algorithm. Force and displacement data is recorded using a National Instruments PCI-6031E data acquisition card.

The software control panel allows the tissue test specimen to be loaded with a variety of excitation waveforms ranging from sinusoidal and ramp functions to that of a single step. Uniaxial tension and compression tests can also be performed and these can be combined with the shear displacements in order to limit fibre stretch of tissues.