**5. Conclusions**

In the present study, we successfully engineered a TPCU electrospun vascular graft which combines appropriate mechanical properties with a highly bioactive surface for the attraction of ECs. The FN biofunctionalization was characterized by a material-driven fibrillogenesis, which might have a positive impact on FN functionality [3]. To imitate the physiological conditions of a blood vessel, a bioreactor for in vitro tissue culture was designed and manufactured. vECs seeded on the FN-functionalized constructs formed a confluent and functional endothelium under static and dynamic conditions. In contrast, DCN-biofunctionalized TPCU scaffolds had a cell-repellent effect on vECs and ECFCs, most likely due to the high hydrophobic properties of the TPCU. However, since DCN has been shown to inhibit the adhesion of fibroblasts, it remains a promising protein for the functionalization of vascular grafts [29].

The challenge for the future will be to combine the advantages of different proteins and to thus increase the selectivity, functionality, and stability of a biofunctionalized vascular graft while keeping the complexity of the coating as low as possible.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/2073-4409/9/3/778/s1, Figure S1: Mechanical characterization of the electrospun TPCU scaffolds and biocompatibility of the materials, Figure S2: Cytotoxicity tests of the materials, Figure S3: Microbiological studies of the ethanol disinfected electrospun TPCU scaffolds, Figure S4: The part of the culture chamber that was considered for CFD simulations, Figure S5: The Poiseuille values (developed wall shear stress value) within the scaffold for different flow rates.

**Author Contributions:** Conceptualization, R.D., D.V., C.W., S.H., U.A.S., M.S. (Martina Seifert), and K.S.-L.; methodology, R.D., D.V., C.W., and M.S. (Maria Schneider); resources, K.S.-L., M.S. (Martina Seifert), L.K., G.L., and M.W.; writing—original draft preparation, R.D.; writing—review and editing, D.V., C.W., M.S. (Martina Seifert), and K.S.-L.; visualization, R.D., D.V., and C.W.; supervision, K.S.-L., M.S. (Martina Seifert), S.H., M.S. (Maria Schneider), and L.K.; project administration, K.S.-L., U.A.S., and M.S. (Martina Seifert); funding acquisition, K.S.-L., U.A.S., and M.S. (Martina Seifert). All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the Deutsche Forschungsgemeinschaft (SCHE701/14-1 to K.S.-L., STO359/13-1 to U.A.S., and SE657/12-1 to M.S.). R.D. was funded by the doctoral program of the University Tübingen "Intelligente Prozess- und Materialentwicklung in der Biometrics (IPMB)" that is supported by the MWK Baden-Württemberg.

**Acknowledgments:** The authors are thankful to Rebecca Haupt for her support in electrospinning, Elke Nadler and Kathrin Stadelmann for the SEM imaging and scientific advice, Elsa Arefaine for the microbiological studies, and Germano Piccirillo for his scientific advice.

**Conflicts of Interest:** The authors declare no conflict of interest.
