Bioengineering of pre-vascularized bone tissue analogues: Laying the basis for a perfusable hierarchical vascular supply

It was the aim of this thesis to bioengineer a hierarchical vascular supply for the application of pre-vascularized osteogenic tissues that are readily perfusable upon implantation. To this end, we were inspired by the organization of the vasculature in the body, where its shape can be described as a vascular tree. Here, large vessels (macrovasculature > 100 μm Ø) facilitate blood flow directly from and to the heart. The macrovasculature branches off into the microvasculature, consisting of mesovessels (arterioles and venules, 10 – 100 μm Ø), that further disseminate the flow into a microcapillary bed to provide blood to the tissues (< 10 μm Ø). Inspired by this architecture, we engineered components of the macrovasculature and microvasculature for the bioengineering of bone constructs in vitro. Here, the macroscale vessel would serve as a point of anastomosis to the patients, and the capillaries would facilitate the exchange of oxygen and nutrients with the cells in the bone tissue analogues. At first, we bioengineered a macrovessel by designing a heterotypic scaffold that was inspired by the layered structure of a native blood vessel. To induce further maturation of these neovessels, we developed a bioreactor system that applied shear stress to the luminal side and differentiated the specific cell layers separately. Secondly, osteogenic tissues with capillary-like structures were generated in hydrogel constructs and later on combined with bioceramics to enhance bone formation in an in vivo setting. As an ultimate goal, the two different levels of vasculature should be interconnected in vitro or in vivo to reach the bioengineering of a vascularized osteogenic tissue, with a point of surgical anastomosis for immediate perfusion. In this thesis, we further provided background information on the envisioned in vivo follow-up study to facilitate the in vivo interconnection in an AV-loop model. Moreover, we proposed a technique to mold the microvascular co-culture model around the macrovessel to enable the in vitro interconnectivity.