Vessels in the void: Microtissue packing for vascular integration in engineered tissues

The field of tissue engineering aims to restore, repair or replace damaged tissue. One of the most researched approaches to achieve this goal is to engineer (parts of) tissue using combinations of materials and cells to restore the function of the damaged tissue. Whereas a number of studies have shown success using small engineered tissues, large implants have typically failed due to inhomogeneous nutrient distribution, leading to starvation and necrotic core formation and, ultimately, implant failure. To enable implant survival of larger (e.g. > cm3) engineered tissues, new solutions are needed to improve nutrient distribution. A common approach is to mimic the vascular system in the human body, for example by self-assembly of vascular cells or bioprinting vascular-like channels within engineered tissues. In this manner, simple channel networks can be created, however they lack the resolution and density of capillary networks, the smallest vessels which ensure fully homogeneous nutrient distribution within tissue. Thus, there is a need for new approaches to prevascularize engineered tissues and mimic the hierarchical vascular networks found in vivo.

This thesis describes i) the development of engineered tissues with inherent capillary-like networks through the bottom-up assembly of cell-laden microfluidically generated living building blocks; ii) the combination of microgel assembly and aqueous two-phase based 3D bioprinting to generate hierarchical channel networks that mimic the vascular tree; iii) the incorporation of insulin releasing beta cells within bottom-up assembled engineered tissues for the treatment of diabetes and iv) a new device to generate cell-laden microfluidic building blocks ranging from the size of a single cell to that of cellular aggregates.

Taken together, this thesis describes a variety of methods as well as tools to enable the generation of prevascularized tissues to facilitate the clinical translation of cubic centimeter sized engineered tissues.