Critical Shear Stress for Re-epithelialization of Tracheal Grafts

Marin, Alba 1, 2 ; Lee, Hankyu 1 ; Aoki, Fabio 3; Karoubi, Golnaz 2, 3; Romero, David 1; Waddell, Tom; 2, 3; Amon, Cristina 1, 2

1.  Advanced Thermal/Fluids Optimization, Modelling and Simulation (ATOMS) Laboratory, Department of Mechanical & Industrial Engineering, University of Toronto, 5 King`s College Rd, Toronto, ON M5S 3G8.; 
 2.  Institute of Biomaterials & Biomedical Engineering University of Toronto;
 3.  Waddell Research Lab Group, Latner Thoracic Surgery Research Laboratories, University Health Network - MaRS Centre, Toronto Medical Discovery Tower

      There are clinical situations in which it would be desirable to replace hollow organs such as tracheae with functional substitutes. Pathologies affecting more than 50% of the tracheal length including large stenosis, malignancy, and traumatic injury usually require long-term dependence on tracheostomies since conventional means of reconstruction are inadequate. These situations seriously deteriorate the patient’s quality of life and increase the medical and social costs. Engineered biological scaffolds are a promising alternative for tracheal transplantation. Epithelial cells play an essential part in tracheal scaffolds but have not been shown in the literature to have efficacious cell–scaffold interactions or functionality, thus limiting graft success. Without successful epithelialization, hollow organs such as the trachea are liable to stenosis, collapse, fibrosis and infections. Beside local surface topography, the mechanical environment experienced by cells has a significant effect in their fate. Many have studied the effect of shear stress on endothelial cell behavior. However, studies with epithelial cells are scarce, and have focused on cartilage, bone, and renal tubular and brain ventricular epithelia. Despite recent advancements, successful epithelialization remains a challenge to graft success. In our work, we aim to optimize the re-epithelialization of tracheal scaffolds by defining the critical shear stress range for adequate adherence and proliferation of the epithelium. To this end, a double-chamber bioreactor is used to accurately control the mechanical stimulation of tracheal constructs, with the goal of recapitulating the host environment. We will characterize re-epithelialized porcine tracheal grafts seeded with HTECs with respect to cell morphology and homogeneous seeding and evaluate the effect of shear stress on cell adhesion, viability and proliferation with different flow rates for dynamic perfusion-cell seeding of de-epithelialized tracheal grafts. As of now, we have re-epithelialized a tracheal graft within a redesigned double-chamber rotating bioreactor with a sensor to monitor the flow rate and, indirectly, the resulting tracheal lumen wall shear stress. The process is currently undergoing improvements, and is expected that ongoing computational fluid dynamics simulations will allow us to enhance re-epithelialization outcomes by optimizing the fluid delivery system.