Clamping soft biologic tissues for uniaxial tensile testing: A brief survey of current methods and development of a novel clamping mechanism.

Biologic tissues are complex materials that come in many forms and perform a variety of functions. They vary widely in composition and mechanical properties, and determination of the mechanical properties of tissues is of interest to those trying to engineer tissues to restore missing function. In performing experiments to characterize the mechanical properties of biologic tissues, there is no single solution to clamping tissues or tissue engineered constructs for mechanical testing. Various clamping techniques have been developed over the past few decades to address the difficulty of imposing appropriate boundary conditions on particular soft tissues during mechanical testing. Two criteria for a successful clamping mechanism are (i) prevention of test specimen slippage, and (ii) prevention of test specimen failure outside the gage region. Herein we present a novel clamping mechanism design developed for the mechanical testing of abdominal wall tissue as an example. This design incorporates pins with serrated clamps to successfully decrease the occurrence of test sample slippage while reducing imposed stress concentrations at the clamping sites. This design was evaluated by performing 40 uniaxial tensile tests on rat abdominal wall muscles using strain rates of 1% per second or 10% per second. Load and displacement data were acquired at the grips. The clamping area on the tissue sample was marked with India ink to track potential slippage of the sample during testing. Ultimate tensile strength and the corresponding stretch were calculated when the maximum load was achieved. With fine-tuning of the torque applied to the clamping grips, the success rate of the tensile tests reached over 90%.