## 4 Discussion
A electro spun composite of spider silk and carbon nano-tubes was employed in a robotic human hand and withstood up to 40,000 bending-stretching cycles while at the same time being able to transmit force as well as electronic signals in term of a feedback system [52]. This application implies possible modifications of native spider silk as well as use of those composites for use in myoelectric prosthetics. On the other hand, further investigations optimizing the conditions of tissue engineering of the pilot study presented herein might lead to optimization of TLC for early in vitro-to-in vivo-strategies. Future studies could also focus on the use of spider silk proteins for 3D tissue printing for example using silk inks [53; 54]. How, beyond the hype and before 3D bioprinted organs are ready to be transplanted into humans, several important ethical issues and regulatory concerns need to be addressed [55; 56]. Another limitation of the study remains the unclear immunocompatibility of the developed TLC. Since the present study is a proof-of-concept study, further investigations are necessary to make conclusive statements about the biocompatibility of the TLC. The use of rat collagen type I would most likely lead to an immunological reaction of the recipient organism, so that an intervention in the intrinsic almoreactivity, e.g., by the use of immunocompressive drugs, would be necessary. It is also conceivable that rat collagen type I is not an optimal matrix material [57]. As published elsewhere, collagens of jellyfish have been intensively studied and showed nearly complete degradation post implantation after 60 days in a rodent model. Furthermore, the degradation process ended in a vessel-rich connective tissue that is understood to be an optimal basis for tissue regeneration [58]. Due to its proven promising immunological properties of native spider silk of species _Nephila edulis_, it is possible to speak overall of a future-oriented biomaterial [22]. However, further analyses are required to determine the optimal composition of the TLC presented here. In the present study, Scx could not be detected in the constructs and no quantitative values could be determined due to interferences of spider silk fibers in polymerase chain reaction (PCR) analysis. Therefore, no definitive conclusion can be made of the influence of mechanical stimulation regarding whether it is superior in terms of expression of different tendon specific markers. However, morphologic analysis revealed better cell alignment towards a tenocyte phenotype. **Author Contributions:** Conceptualization, J.W.K. and F.S. ; methodology, F.S., J.W.K. ; software, F.S., S.S., B.W. ; validation S.S., B.W., and P.M.V. ; formal analysis, F.S., J.W.K., S.S.; investigation, F.S., B.W., C.P., J.W.K. ; resources, S.S., P.M.V. ; data curation, F.S. ; writing--original draft preparation, F.S. and J.W.K. ; writing--review and editing, C.P., B.W., P.M.V., and S.S.; visualization, F.S. ; supervision, J.W.K. ; project administration, J.W.K. ; funding acquisition, J.W.K. All authors have read and agreed to the published version of the manuscript. **Funding:** Parts of this study were funded by achievement-orientated internal funding of Hannover Medical School (HILF) from a grant (No. 79470013) achieved by J.W.K. We acknowledge support by the German Research Foundation (DFG) and the Open Access Publication Fund of Hannover Medical School (MHH). **Institutional Review Board Statement:** The study was conducted according to the guidelines of the Declaration of Helsinki, and approved by the Ethics Committee of Hannover Medical School (Ethics Approval No. 3475-2017; Date of approval: 15 February 2017). **Informed Consent Statement:** Informed consent was obtained of all subjects involved in the study. **Data Availability Statement:** The data presented in this study are available on request from the corresponding author. The data are not publicly available due to privacy reasons.