Engineered, functional, human microvasculature in a perfusable fluidic device

Abstract

Engineered, human tissue models will enable us to study disease more accurately, and develop treatments more economically, than ever before. Functional tissue grown in the laboratory will also provide a much-needed source for the clinical replacement of diseased or damaged tissues. A major hindrance to the development of these technologies has been the inability to vascularize tissue-engineered constructs, resulting in limited size and biological complexity. In this thesis, we report the development of a novel 3D fluidic platform for the generation of functional, human, microvasculature. Using different fabrication methods, we developed both a micro-fluidic system (0.1 - 1 mm tissue dimensions) - used for high throughput disease modeling assays, and a meso-fluidic system (I - 10 mm tissue dimensions) - for generating removable tissue-engineered constructs. These systems were validated by their successful use in a metastasis model - to elucidate the mechanism of cancer cell extravasation, and in the formation of a vascularized, perfusable tissue construct containing pancreatic islets, respectively. Vascularization, in our system, was achieved by encapsulating endothelial cells in a 3D fibrin matrix and relying on their inherent ability to collectively self-assemble into a functional vasculature - as they do during embryonic development. To better understand and characterize this process, we measured the morphological, functional, mechanical, and biological properties of the tissue as they emerged during vascular morphogenesis. We found that juxtacrine interactions between endothelial cells and fibroblasts enhanced the functionality and stability of the newly formed vasculature - as characterized via vascular permeability and gene expression. Under optimal co-culture conditions, the tissue stiffness increased 10- fold, mainly due to organized cellular contraction. Additionally, over the course of 2-weeks, the cells deposited over 50 new extracellular matrix (ECM) proteins, accounting for roughly 1/3 of the total ECM. These results shed light on the mechanisms underlying vascular morphogenesis and will be useful in further developing vascularization strategies for tissue engineering and regenerative medicine applications. Key words: Tissue Engineering, Vascularization, Microfluidics, In Vitro Model.