## 2 Materials and Methods
### Tissue Retrieval and Experimental Trial Applying the Capstan Clamping  
Human flexor digitorum profundus (FDP) tendons were used to evaluate the utility of the capstan clamping system and failure properties of these tendons trialed with the capstan system. FDP tendons feature a central region where the tissues maintain a relatively consistent cross-section, enabling uniform loading within a predefined area of parallel clamping length. The FDP tendons were retrieved post-mortem from human donors at the Division of Macroscopic and Clinical Anatomy, Medical University of Graz, within 72 h of death. The samples were retrieved from eight female and eight male donors, with an average age of 73.0 \(\pm\) 6.4 years at the time of death. Only individuals without musculoskeletal pathologies were included in the study. The FDP tendons were stored at \(-\)80 \({}^{\circ}\)C and thawed prior to testing. The Ethics Committee of the Medical University of  
Figure 2: Components of the capstan testing setup for ligaments (**top**) and mounting procedure (1 to 5) for the capstan experiments (**bottom**).  
Graz approved the use of these tissues as part of a larger biomechanical trial (approval number: 33-189 ex 20/21).  
Before testing, each FDP tendon was prepared by trimming it to a length of 120 mm, and then positioned in an unstretched and non-torqued manner, and to ensure that the region with the minimal cross-sectional diameter was positioned at the midpoint of the sample. This positioning was critical to also ensure uniform stress distribution during testing. The cross-sectional area was measured using silicone casting, as demonstrated in Figure 2. To this end, the silicone was applied to the central tendon region within the area of parallel clamping length. Measurements were taken from that area with the minimal cross-section used for further computations of the mechanical properties.  
Sixteen FDP tendons were then mounted in the capstan clamping system. After securing the spacers bilaterally to the clamping system, the clamps holding the FDP tendons were placed in the testing machine (Figure 2). The T-arm profiles of the spacers were aligned with the gripping bracket to ensure consistent positioning. Once the pneumatic grips were engaged at 2.0 bar, the spacers were removed. Load-failure properties of the FDP tendons were obtained through tensile testing. One sample was discarded due to a software error resulting in incomplete data recording. Each capstan clamping system was discarded after each test to ensure consistency across tests. Additional fifteen FDP tendons were tested to failure, using a squeeze clamping system described elsewhere [5].  
Tensile mechanical tests were conducted at 21 \({}^{\circ}\)C using a quasi-static experimental setup. A ZwickRoell Z020 uniaxial tensile testing machine, equipped with a 2.5 kN load cell and Zwick type 8297 pneumatic grips, was used for the tests (ZwickRoell GmbH & Co., Ulm, Germany). The testing protocol began with an initial preload of 20 N, applied at a speed of 0.10 mm/s. Preconditioning makes an attempt to align the collagen-rich extracellular matrix of ligaments and tendons, thereby recruiting most of the tissue cross-section to participate in load bearing [25; 26]. In the preconditioning phase the specimens were cyclically loaded between 0 N and 20 N using a sinusoidal waveform. A total of 10 cycles were applied at a frequency of 0.05 Hz and a loading rate of 4 N/s. After the completion of the cyclic loading, an ultimate tensile test was conducted at a speed of 0.1 mm/s until sample failure occurred, indicated by a >30% decrease from the previous maximum force. Data collected during testing included the applied force and the vertical displacement of the top bracket for each specimen.