Ph.D Thesis


Ph.D StudentZohar Barak
SubjectIn Vitro Model for Mimicking Intravascular Flow in
Implantable 3D Engineered Tissue
DepartmentDepartment of Biomedical Engineering
Supervisor PROF. Shulamit Levenberg


Abstract

Fabrication of a functional multi-scaled hierarchical vascular network remains an unmet need for cultivation and transplantation of 3D engineered tissues. One promising approach for vascularizing engineered tissue is to utilize the nature of ECs to arranged into a capillary network. In the presented study, we investigate the effect of flow on vascularization. We show how flow stimuli enhance vascular formation and maturation in 3D engineered tissue. Furthermore, we characterize vascularization kinetics using a proprietary multi-channel bioreactor enabling on-line imaging of cells cultured in different construct geometries. Additionally, we developed two models for integrating engineered macro-vessels with self-assembled capillaries to create multi-scale vasculature. The “AngioTube” which is a macro scale biodegradable tube processed in a unique pico-laser drilling technique for achieving a well-defined cylindrical micro channel array. Using both CFD model and particle tracking, we designed and evaluated the flow distribution and characterized the local pressure, velocity and wall shear stress inside the AngioTube. By this model we show how the precise geometry of the engineered micro-channels exclusively guides endothelial cells to form patent micro-vessels which sprout in accordance with channel orientation and anastomose with self-assembled capillaries. The second model is based on fabrication of patterned macro-vessels in a vascularized 3D engineered tissue. The lumen of the macro-vessel is lined with endothelial cells, which further sprout and anastomose with the surrounding self-assembled capillaries for creating a multi-scale vascularized tissue (MSVT). Anastomoses display tightly bonded cell junctions and vessel connectivity is demonstrated by dextran transfer. Additionally, physiological flow conditions are applied with a customized flow bioreactor, to achieve a MSVT with a natural endothelium structure. Finally, implantation of multi-scale vascularized graft in a mouse model resulted in a clear beneficial effect, as reflected by extensive host vessel penetration into the graft and a five-fold increase in blood perfusion via the engineered vessels. These promising results bring a better understanding of flow stimuli in multi-scale vascular architectures for advancing the field of tissue engineering toward transplanting real scale functional organs.