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Vascularization is one of the most central processes enabling multicellular life. Owing to the complexity of vascularization regulatory networks, minor control imbalances often have severe pathologic consequences ranging from ischemic diseases to cancer. Tissue engineers are immediately confronted with vascularization as artificial tissues of a clinically relevant size require a vascular system to ensure vital physiologic logistics throughout the entire tissue and to enable rapid connection to the host vasculature following implantation. Using human umbilical vein endothelial cells (HUVECs) coated onto a human aortic fibroblast (HAF) core microtissue generated by gravity-enforced self-assembly in hanging drops, we created a tissue-culture system for studying capillary network formation. We provide comprehensive technical insight into the design and analysis of prototype vascularization in multicell-type-based microtissues. Detailed understanding of generic processes managing capillary formation in human tissue culture may foster advances in the development of clinical tissue implants.

Heart valve replacement represents the most common surgical therapy for end-stage valvular heart diseases. A major drawback all contemporary heart valve replacements have in common is the lack of growth, repair, and remodeling capabilities. To overcome these limitations, the emerging field of tissue engineering is focusing on the in vitro generation of functional, living heart valve replacements. The basic approach uses starter matrices of either decellularized xenogeneic or biopolymeric materials configured in the shape of the heart valve and subsequent cell seeding. Moreover, in vitro strategies using mechanical loading in bioreactor systems have been developed to improve tissue maturation. This chapter gives a short overview of the current concepts and provides detailed methods for in vitro heart valve tissue engineering.