Case Study: Development of a Biaxial Tensile Testing Machine for Soft Materials and Biological Tissues

Abstract

While uniaxial tensile testing machines are ubiquitous, very few local institutions have access to biaxial tensile testing facilities, and even fewer have machines suited for low-force applications such as elastomers or biological tissues. This case study reports on the design of a custom planar biaxial tensile testing machine, which functioned as a stand-alone desktop tensile tester with two independent, orthogonal testing axes to facilitate the investigation of soft biological materials. Two 50N load cells were used to measure load, and a non-contact Digital Image Correlation system was used to measure three-dimensional surface displacement. Commissioning testing was performed using a silicone elastomer (Smooth-On, Dragon Skin 10) which served as a surrogate for skin. The testing did not seek to characterise the surrogate material, but to verify that the machine operated as intended. Tensile specimens were tested on the custom machine and a commercial tensile testing machine for comparison at four crosshead displacement rates: 10,50,120 and 400mmmin−1. Planar biaxial tensile testing was then performed on cruciform Dragon Skin 10 specimens at the same speeds, but at different speed ratios between the testing axes. The performance of the custom-built machine was critically assessed, and the areas of difficulty encountered during testing were handling and gripping highly pliable specimens, maintaining consistent specimen boundary conditions, and ensuring alignment. The testing demonstrated that the machine functioned as intended and met the requirements for use in testing skin and other membrane tissues in the future.