## 4 Discussion
For example, to overcome issues such as material slippage in uniaxial tensile tests, various adjustments and fixtures have been introduced, including steel clamps with roughened surface areas [8, 11] and high-friction areas [20, 27, 31, 32], cryogenic clamps [12, 13], and pneumatic clamps [1, 5, 9, 28, 32, 33, 34, 35]. However, these existing methods have limitations when applied to soft tissues, particularly due to the risk of avulsion at the clamping site and temperature-induced changes in mechanical behavior [4]. Cryogenic clamps, for instance, create a firm grip by freezing the ends of the specimen, which reduces the need for high clamping forces. However, the application of cold can alter the mechanical properties of the tissue, leading to potential artifacts in the data due to temperature gradients in the gage section. Moreover, the time-sensitive nature of this method, due to the gradual thawing of the specimen, complicates long-term studies and limits its applicability for tissues like tendons, which may respond differently to cold-induced stress. Adhesive-based methods have also been explored, where tissues are bonded to the clamps using cyanoacrylate or other strong adhesives. While effective in preventing slippage and distributing the load evenly, this approach introduces significant challenges in sample preparation and tissue alteration. The bonding process can introduce shear forces that alter the natural state of the tissue, leading to non-representative mechanical properties. Additionally, removing the adhesive after testing can damage the specimen, making it unsuitable for further analysis. In recent years, our team developed a technique called partial plasticity to address material slippage, particularly for soft tissues [2]. Partial plastination minimizes slippage by using ceramic-reinforced polyurethane resins at the mounting sites of the tissue while leaving an area of native tissue for mechanical testing with a sharp boundary to the plasticated area. However, this technique comes with certain limitations, including time-consuming preparation, the need for specialized plastination equipment such as vacuum pumps, explosion-proof facilities and casting fixtures, as well as the use of chemicals such as acetone, with unknown effects on tissue mechanics and potential hazards to the applicant. Its use for tendons, therefore, has not been optimized. Furthermore, positioning soft tissues in a vertical test setup, which involves the effects of gravity, can introduce errors during clamping due to deviations from the axial position, leading to variances in strain and force recordings. In contrast, 3D-printed clamps enable the reduction in slippage and allow for fast handling and simple, reproducible positioning in the testing machine [5,6]. One disadvantage of the existing 3D-printed clamping methods is the need for tapering soft tissues, which can complicate the preparation process and influence the properties if the collagen orientation is unknown. In comparison to these previously described methods, a 3D-printed capstan clamping system offers unique advantages, especially for tendons. It reduces the need for high clamping forces while maintaining the specimen in its natural state, applying a tensile force gradually through the capstan mechanism. This design helps distribute stress more evenly along the length of the tendon, reducing the likelihood of stress concentrations that could lead to premature failure in the clamping region. As a direct consequence of the capstan design, the pneumatic clamping pressure could effectively be reduced from e.g., 6.0 bar [6] to 2.0 bar, which is directly relevant in the context of minimizing stress concentrations at the clamps. Preserving as much of the native geometry and stress distribution across a tissue is crucial for deriving biomechanical parameters, making this approach of using a capstan clamp system particularly advantageous for mechanical testing of tendons.