Assessing the quality of biological tissues using structure-property relationships: macro-scale tests on engineered phantoms.

The overall aim of this work is to determine the quality of biological tissues based on the relationship between the dynamic mechanical properties and their histology. Two sets of rigs have been developed for dynamic mechanical measurement, one for micro-scale testing and the other for macro-scale testing. Preliminary results using the macro-scale measurement system only are reported here. This system uses strain-controlled cyclic probing actuated by a linear stepper motor operating at actuation frequencies between 0.5Hz and 20Hz. A 1mm diameter indenter probes the specimen up to a displacement of 0.2mm and a load cell measures the resultant cyclic force. A series of tissue mimics were prepared using various formulations of gelatin and safflower oil and preliminary tests carried out to determine a suitable range of experimental variables and to establish the repeatability of the tests. The dynamic mechanical properties are expressed as amplitude ratio, phase difference and mean ratios of stress and strain, and the behaviour of these measurands with actuation frequency, mean strain and strain amplitude was observed. Results consistent with the literature were found which form a foundation for measurements on collagen-lipid biological tissues.