## 4 Discussion  
The work presented herein of a 3D-printed clamping system following the capstan principle demonstrated substantial reliability regarding specimen failure site propagation in a desired gage region during uniaxial testing. Using this clamping system, 80% of the FDP specimens failed within the gage section, which is more frequent in comparison to previous 3D-printed designs under similar testing conditions [5,6]. This outcome is in keeping with the primary objective of the study, emphasizing the effectiveness of the capstan design in minimizing stress concentrations in proximity to the clamping region, a common issue with traditional tissue clamping systems [8,11,12,13,20,27], and in tendons in particular [9,10,13]. The ability of the capstan mechanism to distribute tensile forces evenly across the tendon cross-section is likely a critical factor in characterizing biological scaffolds such as FDP tendons in a broad environment of loading scenarios. Besides quasi-static testing of these tissues, fatigue testing is even more challenging, and to derive reasonable S-N (Woehler) curves (where S is the stress range and N is the number of cycles until failure) for such \begin{table}
\begin{tabular}{c c c} \hline \hline
**Sample** & **Loading Behavior** & **Initial Rupture** \\ \hline
10 & continuous & gradual \\
11 & continuous & abrupt \\
12 & 1 micro-step & abrupt \\
13 & continuous & gradual \\
14 & 2 micro-steps & abrupt \\
15 & 1 micro-step & gradual \\ \hline \hline \end{tabular}
\end{table} 
Table 2: _Cont._  
Figure 4: Load–deformation behavior, exemplifying in four categories. **Top left**: continuous deformation, gradual rupture; **top right**: deformation under several micro-steps prior to abrupt failure; **bottom left**: several micro-steps prior to gradual failure; **bottom right**: continuous deformation, followed by abrupt rupture. tissues further amplifies clamping-related issues [6, 28, 29]. Based on the results of this study, our hypothesis, that by using a capstan clamping design, mechanical failure occurs more frequently in the mid sample region when compared to our previous 3D-printed mounting technique [6], can therefore be approved. The reasoning for the broad variation in loading behavior and failure characteristics within the tissues cannot be entirely elucidated at this point, but is likely related to the intrinsic material properties, and potentially to the in vivo loading history of the tissues prior to sample retrieval. The observed variability in the cross-sectional areas and mechanical properties of the FDP tendons is consistent with the biological diversity and size range typically reported in the literature [3, 30]. Despite this inherent variability, the elastic modulus and ultimate tensile strength values measured in this study were within an expected range [29]. Interestingly, a relatively low coefficient of variation has been observed for the different tissues (\(\text{CV}_{\text{Elastic modulus}}=0.27\), \(\text{CV}_{\text{Ultimate tensile strength}}=0.24\), and \(\text{CV}_{\text{Fmax}}=0.18\)), lower than can be expected from similar trials on collagen-rich tissues [3, 30]. This finding supports the argument in favor of capstan clamps to improve the reliability of failure occurring in the mid-section of the tissue, thus helping to minimize bias introduced by the experimental setup. The results from this study underscore the importance of employing a consistent and reliable clamping method to obtain reproducible data in biomechanical studies [3, 30]. Potential Advantages of Capstan Clamping in Overcoming Challenges in Uniaxial Tensile Testing of Soft Tissues  
The use of a capstan clamp system described herein can potentially overcome many of the issues that can be imparted by some traditional clamping methods in mechanical testing.