Biaxial testing instrument

Our unique rig measures boundary forces and strain fields throughout the sample. Biological membranes, such as skin, are typically intricately structured heterogeneous materials, exhibiting complicated mechanical behaviour. These behaviours include:

• Anisotropy
• Viscoelasticity
• Non-linearity
• Inhomogeneity
• Marked differences between individuals

In order to characterise the mechanical properties of such materials, the membrane must be subjected to a rich set of deformations and analysed using model-based methods.

Our unique biaxial testing device enables us to measure the mechanical response of membranes, and identify their underlying properties through inverse modelling approaches. You can find the instrument in our Bioinstrumentation Lab.

• The instrument is equipped with 16 actuators, arranged in a circular array, each capable of moving up to 50 mm with a resolution of 2 µm. Each actuator is equipped with a custom-built 20 N 2D force transducer, from which the applied force vectors at each of the 16 attachment points are recorded. 
  
• An area scan camera is used to record the geometry and the internal deformations of the samples. The deformations of regions within the geometry are traced mathematically as displacements of subimages (typically 16 pixel to 128 pixel square) using a phase-based cross-correlation technique (HajiRassouliha et al. 2017). This technique is able to resolve displacements to 0.-01 pixel, giving displacement resolution better than 1 μm.
• The optical properties of the samples can be simultaneously measured using a full Mueller matrix imaging system. This capability is useful to characterise the distribution of optically active constituents, such as collagen, in each sample. 
• The instrument has been used to identify the mechanical behaviour of living skin at various places on the body, across many individuals. The equipment and analysis, however, are able to characterise the mechanical behaviour of a wide range of membranous materials.

Professor Poul Nielsen
Phone: +64 9 923 8391
Email: p.nielsen@auckland.ac.nz
Directory information: Poul Nielsen

Professor Martyn Nash
Phone: +64 9 923 2550
Email: martyn.nash@auckland.ac.nz
Directory information: Martyn Nash

Associate Professor Andrew Taberner
Phone: +64 9 923 5024
Email: a.taberner@auckland.ac.nz
Directory information: Andrew Taberner

Dr Thiranja Babarenda Gamage - Research fellow
Phone: +64 9 923 3010
Email: tp.babarendagamage@auckland.ac.nz
Directory information: Thiranja Prasad Babarenda Gamage

Alex Dixon - PhD student
Phone: +64 9 923 3010
Email: adix022@aucklanduni.ac.nz
Directory information: Alex Dixon

We are grateful for the help given to us by:

• Skin NERF
• MSI (TechNZ grant)