## 3 Results and Discussion
### 3D Braided Structures Based on PCL/CNC Wet-Spun Filaments  
The organization of the fibrous matrix in tendons and ligaments is crucial for supporting loads and maintaining function. In tissue engineering, creating filament-based structures from biomaterials can mimic this fibrous orientation, aiding in ligament repair. However, a single filament lacks the strength to replicate the natural load-bearing capacity of ligament structures. To address this, a braiding machine was employed to produce more compact and mechanically robust structures from the optimized 30% PCL + 3% CNC filaments. Initial attempts using a single filament per spool for braiding resulted in frequent breakage, demonstrating that single filaments could not withstand the tension during the process. To improve strength, twisted filament bundles were introduced. After testing configurations with 5 and 8 twisted filaments, the optimal configuration was determined to be 10 twisted filaments per spool. This setup provided sufficient mechanical stability and allowed for continuous production without breakage. Four different braided structures were produced, each varying in core size to explore their impact on mechanical properties and structure integrity. The structures included a compact design without a core (0 mm core) and three with core diameters of 2 mm, 4 mm, and 6 mm. The use of a core during the braiding process helped maintain the desired structure size, but it was removed after braiding to produce hollow tubular forms. Figure 5  
Figure 4: BJ-5 ta cell viability was measured by MTS assay at: (**a**) 24 h and (**b**) 48 h of culture with undiluted conditioned media and with different dilutions of the conditioned media (1:2–50/50, 1:4–25/75, and 1:5–20/80) preconditioned for 24 h by contact with the PCL and PCL/CNC filaments. The data represent the mean \(\pm\) SD of one independent experiment, each with triplicates. Life and death control of the MTS assay at (**a**) 24 and (**b**) 48 h of culture. Statistically significant differences were achieved by comparing the results with the control. \(\boldsymbol{\texttt{{}^{***}}}\)\(p\)\(\leq\) 0.0001 when compared with life control. shows the resulting braided structures, labeled as follows: (a) S1--0 mm core, (b) S2--2 mm core, (c) S3--4 mm core, and (d) S4--6 mm core. To preserve the structural integrity and desired shape, the braided structures were heat-treated at 40 \({}^{\circ}\)C for 30 min. This step stabilized the braiding, ensuring that the filaments retained their orientation after the core was removed. Detailed analysis, including microscopy images and measurements of the average diameters with standard deviations, is presented in Figure 5 and Table 3.  
Microscopic analysis revealed that larger samples showed wider braid spacing, while smaller samples had more homogeneous structures. The values of average structure diameter were found to be 3.394 mm for S(a), 3.805 for S(b), 5.992 for S(c), and 7.162 for S(d). The natural ACL diameter range is in the same range (4-10 mm) [32; 52], which shows the potential application of the four structures on ACL replacement. For a more detailed analysis of the produced structures, FESEM was used to assess the surface morphology and internal organization of the braided constructs. Figure 6 shows the FESEM images of compare two representative structures: the most compact configuration (S(a)--0 mm core) and the structure with the largest core (S(d)--6 mm core), allowing to evaluate overall filament organization and morphology and for a closer examination of the surface characteristics. Figure 5: Microscope images of the structures produced with different core sizes: (a) 0 mm; (b) 2 mm; (c) 4 mm; and (d) 6 mm. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Sample** & **Average Diameter (mm)** & **Standard Deviation (mm)** \\ \hline (a) & 3.394 & 0.037 \\ (b) & 3.805 & 0.020 \\ (c) & 5.992 & 0.042 \\ (d) & 7.162 & 0.063 \\ \hline \hline \end{tabular}
\end{table}