Abstract

Biofabrication of Vascularized Tissues with Bioprinting

Heidi Declercq, Postdoc Scientific Researche, Universiteit Gent

The main challenge in tissue engineering is the creation of a functional engineered vascular system with multiscale vessel networks from capillaries to large vessels within complex 3D structures such as heart, muscle, bone, adipose tissue,… Strategies to engineer these tissues can be categorized in top-down, scaffold-based approaches and bottom-up, developmental biology inspired approaches (scaffold-free). In the bottom-up approach, a 3D tissue is build by assembling modular tissues (spheroids).

In this lecture, we will focus on combining the advantages of both approaches that will have a synergistic effect on fabrication of 3D tissue analogs. In our approach, cellular building blocks with self-assembling properties and mimicking the tissue of interest will be combined with cell instructive biomaterials. The cellular building blocks are either tissue-specific or vascular. Using a high-throughput non-adhesive agarose microwell system (2865 pores, diameter 200 µm) uniform spheroids with an ideal geometry and diameter (< 200 µm) for bioprinting are formed. High quality homocellular building blocks were already generated that form tissue-specific cellular building blocks ((fibro)cartilage, adipose tissue, bone tissue,…) starting from adult cell types or human mesenchymal stem cells derived from adipose tissue or pulp tissue. Dependent on the tissue type, stable spheroid formation was influenced by cell culture medium, environment and cell types. These tissue-specific spheroids can be combined with vascular spheroids providing the capillary like network. By coculturing endothelial cells with supporting cells (fibroblasts and/or adipose tissue derived mesenchymal stem cells), and applying the favourable coculture ratio, viable vascular spheroids were obtained. Endothelial cells spontaneously organized into a capillary like network and lumina were formed. Moreover, the spheroids were able to assemble at random in suspension, creating a macrotissue. The tunable mechanical characteristics of hydrogels (crosslinking efficiency) can influence outgrowth and fusion of the spheroids. 3D bioprinting of vascular spheroids in photocrosslinkable gelatin-methacrylamide was performed with the 3D Discovery (RegenHu) and resulted in high viability and fusion of the vascular spheroids into a vascular network. Reorganization of cells, throughout the entire fused construct and by inoculating with capillaries of adjacent spheroids, creates a branched capillary like network

Combining the advantage of the natural capacity of microtissues to self-assemble and the controlled organization by bioprinting technologies, these vascularized spheroids can be useful as building blocks for the engineering of large vascularized 3D tissues.