Evaluation of soft-tissue properties under controlled expansion for reconstructive surgical use

The field of tissue surgery using silicone inflatable expanders presently relies on a surgeon's qualitative prediction of the tissue yield during the expansion regime. This work examines the viscoelastic behaviour of pig tissue whilst undergoing expansion and compares the results with classical tensile test methods. Close correlation between the stress relaxation constants for each method is found. The time relaxation of the tissue conforms to a quasi-linear viscoelastic model which enables the time to achieve the maximum viscous tissue yield to be determined. The elastic fraction of tissue has been shown to increase progressively with increasing applied strain whilst the viscous fraction decreases. The greatest tissue yield is generated at low strains and is largely due to the reorientating of the collagen matrix in the direction of the applied stress. This analysis suggests that it may be possible to develop a set of protocols to control and quantify the generation of new tissue during an expansion regime.