For a lay summary of the thesis presented in a 1-minute video format, visit the following link: https://www.youtube.com/watch?v=VhLzt_tEz-s / It is projected that, by 2030, 8% of all adults in the world will have diabetes mellitus and treatment will account for 10% of the total healthcare budget in many countries. Polymeric biomaterial research has led to the design of robust polymer hydrogel capsules to develop curative cell-based therapies for chronic disorders such as diabetes mellitus. Encapsulation of insulin-producing beta cells within synthetic, semi-permeable polymer hydrogels can avoid host immune rejection including fibrotic responses, and thus holds the promise of a long-term curative treatment of this disease. There is a paucity of literature regarding methods available for standardized in vitro screening of synthetic polymer hydrogel capsules to predict host responses in vivo. Thus, the focus of this thesis was to design in vitro assays able to screen for subsequent in vivo fibrotic responses. Two dimensional (‘2D’) (cell attachment to thin film hydrogel coatings) and three dimensional (‘3D’) (cell attachment and protein adsorption to hydrogel capsules) in vitro experiments were designed and tested in an iterative process to assess fibrotic responses to a diverse group of polymer hydrogels. Cell attachment assays included fibroblast (NIH 3T3) and macrophage (RAW 264.7) cell lines, and protein adsorption assays included proteins used to model fibrosis including fibrinogen and lysozyme. For some formulations, in vitro assays were compared with in vivo data on pericapsular cellular overgrowth (PCO) after being implanted into mice. A binomial logistic regression model was designed and validated to assess whether the ‘3D’ in vitro assays correlated with in vivo PCO responses. It was found that the RAW 264.7 cell attachment assay was significantly correlated with PCO outcomes in vivo, demonstrating for the first time a simple, cost-effective, and rapid in vitro cell-based approach to screen and select capsules with lower fibrotic potential to be further tested in animals. / Thesis / Master of Health Sciences (MSc) / In North America, one in eleven adults, or about 415 million people, have diabetes. It is projected that by 2030, around 8% of the world population will be diagnosed with this disease. A common form of treatment is through the frequent injection of insulin, but this is costly, requires multiple daily interventions, and cannot prevent regular excursions from the ideal blood glucose range. Cell-based therapies have a lot of promise in treating several chronic diseases including diabetes. Donor and stem-cell derived islets can be implanted into patients with type 1 diabetes and have been shown to function for over a year, albeit at the price of systematic immune suppression. Alternatively, cells that produce insulin can be placed inside immune-evasive capsules and implanted, potentially providing continuous blood glucose regulation without the need for daily insulin injections. However, this novel form of treatment is limited by the encapsulated cells’ survival once implanted. Cell survival can be affected by the body’s response to a foreign body (the capsule), causing deposition of protein or cells on the capsule surface which can limit the oxygen supply to cells in the capsule and the ability of insulin to leave the capsule in a timely fashion. The goal of this project is to develop assays to screen new capsule formulations. This can advance research by using capsules more readily accepted by the body, leading to a more promising and long-term treatment of diabetes.