## 3 Results
In comparison, constructs of experimental group G had shrunk to 13.8 \(\pm\) 1.3% of their initial length whereas constructs of experimental group H had shrunk to 15.1 \(\pm\) 1.0% of their initial length. To sum up, constructs with 5 \(\times\) 10\({}^{6}\) ASC showed a more pronounced contraction over the study period of 30 days. Constructs of experimental group G and H were too short to ensure a stable fixation of constructs in the bioreactor. Consequently, 5 \(\times\) 10\({}^{5}\) ASC were used for all further experiments. Mechanical Induction of ASC Differentiation Using the Custom-Made bioreactor Showed Macroscopic Results Comparable to Tendon Tissue  
As described above, custom-modified bioreactors were made and constructs stressed with a uniaxial strain. A total of five constructs could be cultivated in parallel in the bioreactor. Two constructs with spider silk (experimental group A) and two constructs without spider silk (experimental group B) were stressed in the bioreactor per cycle and the three cycles were performed in total. No bacterial contamination was observed over the experimental period of 30 days. It was macroscopically observed that constructs containing spider silk were more stable in handling. Furthermore, after 21 days of mechanical stressing the constructs showed a phenotype which had the first morphological signs that could be indicative of ASC differentiation towards tenocytes. No differences could be observed between experimental groups A and B (Figure 4). Histological Analysis Shows Long-Term Cell Survival and Histological Patterns Comparable to Tendon Tissue  
The LIVE/DEAD stain showed that the majority of cells were viable in all experimental and control groups after a period of 30 days (Figure 5). Only a negligible number of cells were dead. In addition, a low cell density was observed in all constructs and no significant differences between experimental groups could be detected. As seen in Figure 5A,C, truncated spider silk fibers showed a reddish autofluorescence. However, an orientation of cells and silk fibers towards the direction of mechanical stimulation was observed in experimental groups (Figure 5A,B). Compared to those constructs, controls showed a less aligned orientation of cells (Figure 5C,D). On trend, lower cell density was found in constructs with mechanical stimulation compared to those without mechanical stimulation. Figure 4: Tendon like constructs after 21 days of mechanical stressing using the bioreactor. The top one contains spider silk (experimental group A), the bottom one is manufactured without spider silk (experimental group B). The constructs showed phenotypes comparable to tendon tissue with no difference between experimental groups A and B. In Masson-Golder Trichrome staining, microscopically collagenous connective tissue is green, the nuclei brown-black, the cytoplasm red and the muscles pale red. Elastic fibers often do not show a specific color and can be greenish or light red. The tendon-like constructs of the experimental group A showed a clear orientation of the collagen fibrils and the spider silk fibers along the direction of mechanical tension (Figure 6A). The cells showed an elongated cell phenotype comparable to tenocytes (Figure 6A). In experimental group B, collagen fibrils and spider silk fibers showed an orientation along the direction of the mechanical tension as well (Figure 6B). Overall, cells in the mechanically stimulated TLC showed a broad distribution within the matrix (Figure 6A,B) whereas the unstimulated controls showed the formation of coherent cell formations (Figure 6C,D). Compared to experimental group A, cells showed an elongated cell phenotype as well but also formed coherent cell formations especially at the edges of the tendon-like constructs (Figure 6B). In experimental group C and D, collagen fibrils as well as spider silk fibers showed no coherent orientation and cells showed a more roundish phenotype (Figure 6C,D).