An Apparatus for Measuring Combined Shear-Tensile Loading in Fibrous Tissues Ex Vivo

Soft tissues such as tendon and ligament undergo a combination of shear and tensile loading in vivo due to their boundary conditions at muscle and/or bone. Current experimental protocols are limited to pure tensile loading, biaxial loading, or simple shear, and thus may not fully characterize the mechanics of these tissues under physiological loading scenarios. Our objective was to create an experimental protocol to determine the shear modulus of fibrous tissues at different tensile loads. We assembled a four-actuator experimental system that facilitated shear deformation to be superimposed on a tissue subjected to an axial preload. We measured shear modulus in axially loaded electrospun nanofiber scaffolds with either randomly oriented or aligned fibers. We found that shear modulus in the nanofiber phantoms was shear-strain stiffening and dependent on both the axial load (p < 0.001) and fiber alignment (p < 0.001) of the scaffold. The proposed system can enhance our understanding of microstructure and functional mechanics in soft tissues, while also providing a platform to investigate the behavior of electrospun scaffolds for tissue regeneration. Our experimental protocol for determining loaded shear modulus would be further useful as a method to gauge tissue mechanics under loading conditions that are more representative of physiological loads applied to tendon and ligament.