## 4 Discussion
External damage to the tissue in the clamping areas was reduced when compared to conventional clamping by metal jaws. Such findings have already been quantified in another study by our group [15]. Moreover, the handling and insertion into the testing device was simplified due to the modular setup, resulting in a time advantage when handling the tissues. The time required for specimen preparation, mounting, and testing was not bound to the additional time needed for hardening of the embedding material, such as epoxy resin, which was used in a previous study [13; 28]. The clamp-to-clamp length is predefined by the holder arms and therefore standardized for every test carried out. In addition, the alignment and tested region of the samples is exactly defined before the insertion and does not require manual adjustment in the testing machine. An occurrence of improper sample alignment during clamping or sample damage (e.g., by the jaws) during insertion was not observed when using the 3D-printed system. All of the given adjustments of the clamping and mounting devices were made in favor of providing a standardized, time efficient, and easy-to-handle design, resulting in the first successful attempt to obtain fatigue curves of human tendon samples while at the same time minimizing material slippage to achieve >10\({}^{5}\) loading cycles ex vivo. In addition to their ease of use, all parts of the clamps and mounts are highly accessible and easy to adapt. The design of the clamps and holder arms can be customized to suit various soft tissues of different dimensions and lengths. Another advantage when using 3D-printing technology is the freedom to choose the most suited printing material. PLA used in this study is a commonly used and accessible filament printing material and is biodegradable [33]. Therefore, depending on the material chosen, 3D-printing technology allows for the reduction of non-degradable waste in biomechanical testing. Due to a lack of reliable and standardized methodical cyclic testing of soft tissues, no data are available to date to predict tissue behavior under cyclic loading; 3D-printing technology provides accessibility, ease of use, and adjustability, as well as sustainability and may therefore be the infrastructure for the future assessment of soft tissues. This standardized method may provide the opportunity to learn more about the mechanics of tissue. The design of the presented clamps is optimized for less compressive biological samples with a thicker cross-sectional area and may be used for various types of biomechanical testing. There are various factors influencing the mechanical behavior of soft tissues, which to date have not been fully quantified. The load-deformation characteristics of tendons, ligaments, and other soft tissues are individual and may change with age, injury or disease, and other factors. Facilitating and standardizing the assessment of these materials may enable us to better understand the story behind the tissue--how it influences its mechanical behavior and quantifies its mechanical age. Gaining a better understanding of how tissues change may provide valuable information for the optimization of treatments to avoid injuries or improve surgical treatments and rehabilitation after injury. Further, the here-given setup may allow for assessing tendon (fatigue) damage at substructural levels, elucidating site-different mechanical behavior of tendon structures [34].