"Vascularization, the process in which new blood vessels assemble, is fundamental to tissue vitality. Vessel network assembly within 3D tissues can be induced in-vitro by means of multicellular culturing of endothelial cells (EC), fibroblasts and cells specific to the tissue of interest. This approach supports formation of endothelial vessels and promotes EC and tissue-specific cell interactions. Such EC-dependent tube-like openings may also form the basis for improved media penetration to the inner regions of thick 3D constructs, allowing for enhanced construct survival and for effective engineering of large complex tissues in the lab. Moreover, our own breakthrough results describe the beneficial impact of in vitro prevascularization of engineered muscle tissue on its survival and vascularization upon implantation. These studies have also demonstrated that implanted vascular networks of in vitro engineered constructs, can anastomose with host vasculature and form functional blood vessels in vivo. However, the mechanisms underlying enhanced vascularization of endothelialized engineered constructs and implant-host vessel integration remain unclear. In this proposal, our research objectives are (1) to uncover the mechanisms governing in vitro vessel network formation in engineered 3D tissues and (2) to elucidate the process of graft-host vessel network integration and implant vessel-stimulated promotion of neovascularization in vivo. In addition, the impact of construct prevascularization on implant survival and function will be explored in animal disease models. While there are still many challenges ahead, should we succeed, our research could lay the foundation for significantly enhanced tissue construct vascularization procedures and for their application in regenerative medicine. In addition, it may provide alternative models for studying the vascularization processes in embryogenesis and disease."