Access Type

Open Access Embargo

Date of Award

January 2020

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Chemical Engineering and Materials Science

First Advisor

Howard W. Matthew

Abstract

Every year thousands of people in U.S die due to lack of organ available for transplantation. The goal of tissue engineering is to fabricate and generate functional, multicellular tissue structures in-vitro, capable of mimicking the organ or tissue specific function. These tissue structures can later be transplanted in-vivo to replace the damaged organ and tissue or can be used inside the in-vitro culture and organ-on-chip systems to study the specific organ and organ related disease. The traditional approach in tissue engineering or the top down approach possess multiple drawbacks including lack of vascularization and inability to form large 3D tissue structures. On the other hand, modular tissue engineering approach can address these limitations by generating smaller modular components such as microcapsules and hollow fibers to be assembled to form a larger 3D tissue structure.

In this study, we investigate the design and fabrication of two type of tissue structures namely microcapsules and hollow fibers using efficient, high throughput techniques which make them great options to be used in the point of care. Electrospraying method was studies as a rapid and convenient technique to encapsulate mesenchymal stem cells (MSCs) and their differentiation into cartilage tissue was studied in detail. Microcapsule created a genuine microenvironment for MSCs growth and differentiation by providing the required ECM proteins such as collagen and proteoglycans for cells. We further demonstrated that MSCs differentiation into chondrocytes could be accelerated by using a perfusion culture system and providing a low oxygen concentration for MSCs inside the microcapsules. This platform has the potential to be used as a cartilage tissue regeneration using MSCs as a cell source for treatment of osteoarthritis.

We also demonstrated the application of microcapsules in liver tissue engineering by creating a multicellular structure inside the microcapsules. In this study, hepatocytes alongside MSCs and vascular endothelial cells (VECs) were co-encapsulated inside the microcapsules to create a vascular and dense tissue mimicking the liver structure. Hepatocytes showed to preserve their metabolic activity up to 28 days of culture in the perfusion culture which can be used for drug toxicity tests and liver disease studies. VECs also formed a vascular network inside the microcapsules facilitating the transport of oxygen and nutrient into the hepatocytes. Aside from the application of hepatocytes microcapsule in building liver-on-chip models for drug toxicity tests, they also have the potential to replace the damaged part of the liver. Hollow fiber is another component of our modular structure which can mimic multiple tissues inside our body including vein, arteries, and bile ducts. In this study, hollow fibers were fabricated using a novel dip coating method and were seeded internally with liver epithelial cells to mimic the liver bile duct. These hollow fibers represented the bile modification characteristic same as the native bile ducts inside the liver which verified their successful function and activity in our in-vitro culture system. The artificial bile ducts fabricated in this study are the first step in building a fully functional bile duct to replace the damaged bile duct in patients suffering from biliary atresia and ischemic cholangiopathy. We further assembled our hepatocyte microcapsules with the artificial bile duct fabricated inside a liver-on-chip model to mimic the physiology and function of the native bile duct. To the best of our knowledge this is the first study done on mimicking the physiology of the bile duct using both the parenchymal and non-parenchymal liver cells. This research represents the promising potential of microcapsules generated using the electrospaying method and hollow fibers fabricated using the dip-coating method to create dense, multicellular 3D tissue structures to be used inside the in-vitro culture systems for organ related studies in addition to their application in generating dense 3D tissue to replace the damaged organ or tissue.

Available for download on Thursday, January 27, 2022

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