A modular low-cost and open source device for combined axial-torsion testing of soft materials.

Mechanical characterization of soft materials is essential for understanding their response to external loading and informing functional performance. Soft biological tissues are structurally organized systems whose mechanical behavior depends on cells, the extracellular matrix, and biological processes, including disease. Their experimental characterization requires systems capable of reproducing physiologically relevant loading modes. However, most experimental approaches rely on simplified loading conditions. Moreover, commercial multiaxial platforms are often costly and lack flexibility for biopsy-scale testing in hydrated environments. We developed a modular, low-cost device for combined axial compression and torsion. The system was constructed using commercial components and 3D-printed fixtures, enabling controlled axial and torsional deformation within a configurable architecture costing below $12,000. Silicone validation demonstrated low error between theoretical and torsion-measured shear moduli. Using porcine right ventricular myocardium, we evaluated device performance under cyclic loading. The system demonstrated reproducible measurements and captured key features of soft tissue behavior, including nonlinear strain-stiffening and viscoelastic hysteresis. It further enabled investigation of compressive preload effects on torsional response, showing that toe stiffness, calf stiffness, and hysteresis decreased with increasing compression. These findings demonstrate that compressive preload modulates the apparent torsional response of myocardium and support the need for multiaxial testing approaches in soft tissue biomechanics. This work establishes an accessible and configurable platform for combined axial-torsion testing at the biopsy scale and provides a tool for mechanically relevant characterization of soft materials under controlled multiaxial loading.