Biomaterial-based devices for liver cell transplantation
The liver performs over 500 functions and plays an integral role in maintaining the proper function of the body. Any change to the complex liver structure can disrupt proper function and result in liver diseases or disorders. Approximately 30 million people in the United State have some form of liver disorder. These disorders can be genetic, example hemophilia B, virus based, example hepatitis C, or lifestyle based, example alcoholic liver disease. Currently, while there may be treatments for some liver disorders, the only long-term cure for all liver disease or disorder is whole or partial organ transplantation. However, there is a significant shortage of transplantable donor organs, which has led to about 27,000 deaths annually attributed to liver disease in the United States alone. To combat this issue researchers are studying different cell therapies to either engineer whole livers as an alternative source for organ transplants; use cell therapies to replace damaged cells and stimulate liver regeneration; or use cell therapy in ex vivo devices as a way to extend a patient’s life expectancy and bridge the gap until a donor organ is available. In this dissertation, I have engineered novel devices for liver cell transplantation by focusing on optimizing methods for maximizing cell delivery in vivo and maintaining long-term function. With these devices I have developed vehicles for autogeneic, allogeneic and xenogeneic liver cell transplantation to provide alternatives or improvements to existing liver therapies.
Chapter 1 is a literature review focusing on the use of biomaterials in hepatocyte culture and transplantation. Specifically, in this chapter, I underscore the role of biomaterials in improving in vivo hepatocyte culture techniques to help establish a more reliable and readily available cell source for transplantation therapies. Since primary human hepatocytes have limited availability, I also discuss the role of biomaterials in improving stem cell derived hepatocyte culture. Next, I highlight the most recent advancements in the use of biomaterials for engineering 3D constructs for transplantation. Specifically, I focus on the work that has been done using decellularized liver scaffolds for recellularization and transplantation, and the use of hydrogel based scaffolds for encapsulation and transplantation of cells.
Because the success of cell therapies hinges on the proper delivery, engraftment and long-term function of a large number of cells, in Chapter 2, I engineered transplantable tissues for applications in liver related cell therapies. Firstly, I have developed a dual compartment system for minimally invasive, subcutaneous implantation of 3-D vascularized liver-like tissues. In this system an inner compartment houses large numbers of primary hepatocytes, while the outer porous compartment facilitates vascularization to support sustained hepatocyte function. When implanted into NOD/SCID mice, this system has shown sustained function for at least 1 month in vivo as evidenced by human serum albumin secretion and immunostaining.
While the dual compartment system facilitates host cell recruitment for vascularization, making it an intervention better suited for autogeneic, immunosuppressed interventions; it is not suitable for allogeneic or xenogeneic transplants. To address this, in Chapter 3 I developed a biocompatible device that is closed off from host cell infiltration yet still allows flow of necessary nutrients and waste in and out of the implant, through the selectively permeable chitosan membrane. The device was further optimized through surface modification to prevent adhesion of immune cells and fibroblasts and subsequent fibrous capsule formation. While chapter 3 focuses on the development, modification and characterization of the pouch, chapter 4 focuses on the application of the pouch in allogeneic and xenogeneic transplantation. Allogeneic and xenogeneic transplantation success of this device to maintain cell function was shown through ELISA and immunostaining analysis.