Fatigue Testing of Human Flexor Tendons Using a Customized 3D-Printed Clamping System

Featured Application This novel 3D-printed clamping design allows for time efficient and seamless cyclic testing of biological soft tissues to obtain fatigue curves without the need for processing. Improved surgical procedures and implant developments for ligament or tendon repair require an in-depth understanding of tissue load-deformation and fatigue properties. Cyclic testing will provide crucial information on the behavior of these materials under reoccurring loads and on fatigue strength. Sparse data are available describing soft tissue behavior under cyclic loading. To examine fatigue strength, a new technology was trialed deploying 3D-printing to facilitate and standardize cyclic tests aiming to determine tendon fatigue behavior. Cadaveric flexor digitorum tendons were harvested and mounted for tensile testing with no tapering being made, using 3D-printed clamps and holder arms, while ensuring a consistent testing length. Loads ranging between 200 to 510 N were applied at a frequency of 4 Hz, and cycles to failure ranged between 8 and >260,000. S-N curves (Woehler curves) were generated based on the peak stresses and cycles to failure. Power regression yielded a combined coefficient of determination of stress and cycles to failure of R-2 = 0.65, while the individual coefficients for tissues of single donors ranged between R-2 = 0.54 and R-2 = 0.88. The here-presented results demonstrate that S-N curves of human tendons can be obtained using a standardized setting deploying 3D-printing technology.