Bioinstrumentation Development

Bioinstrumentation development is a core component of the Auckland Bioengineering Institute. Novel sensors and instruments continue to provide new physiological data and facilitate the derivation of model parameters in a variety of application areas. Excellent laboratory and workshop facilities are available with specialist equipment for electronic and mechanical prototyping, and wet tissue experimental facilities. Specialist skills cover sensors, imaging, signal conditioning, motion control and analysis, telemetry, micro-fabrication, inductive power transfer and tissue preparations.

• Group members and collaborators
• Project publications

The Biaxial rig was custom built to investigate the mechanical properties of soft tissue membranes, such as skin. A circular array of sixteen displacement actuators (Physik Instruments) and 2D force transducers are used to impose deformations in the tissue sample. Internal displacements are monitored with a CCD camera (Atmel) and measured using a cross-correlation technique. All data acquired during an experiment are post-processed using a finite element analysis (software CMISS) to allow parameter estimates to be determined for material laws. The Multiaxial Rig and the corresponding numerical techniques have successfully established a constitutive model for the stress-strain behaviour in human skin.

We have developed a superfused muscle bath, suitable to determine both passive and active mechanical properties of cardiac trabeculae (~2 mm long x 200 µm diameter). These properties are determined by mechanically perturbing one end of the trabeculae while measuring the resulting force changes at the opposing end. Stiffness is determined via small amplitude high frequency displacement, while compliance (stress-muscle length) is determined via larger and slower displacement. The 40 µl muscle bath is constructed of two coverslips spaced at 2 mm attached to a brass base. The brass base is temperature regulated via a Peltier thermode. The coverslip walls of the bath offer an optical path through which a 50 times objective captures a 120 x 90 µm subimage of the trabeculae.

UnEmap is a high channel count electrophysiological mapping system. It is an integrated system with specialised electrode developments, analogue signal conditioning and data acquisition hardware together with software designed for processing, analysis and display of a large number of data channels. Uniquely, any number of channels can be accommodated (largest system supplied has 1972 electrodes) and it is possible to record from, or pace down each individual electrode. It is being used extensively for cardiac based animal and human research. New developments are concentrated on electrode systems, and providing additional software features, often tailored to specific client requests. Systems have been supplied to the UK, US, Australia, Belgium and New Zealand.

Elastic socks, such as that shown in the figure (above left), are used to map electrical activation on the epicardial surface of the heart. These contain up to 384 electrodes which move with the myocardium as the heart beats. Flexible plaques with closely spaced electrodes (see figure left) are used to map electrical activation at higher spatial resolution mapping, for instance, in studies of atrial fibrillation. Very high density electrode plaques (around 100 µm spacing) and intramural needle probes, 500 µm diameter and containing up to 13 electrodes, are also manufactured.

The Bioinstrumentation Development Project gratefully acknowledges the support of its funding partners:

• New Economy Research Fund
• Pre-seed Accelerator Fund
• Health Research Council of New Zealand
• UnEmap