Transplantation of encapsulated pancreatic islets is a treatment for type 1 diabetes that has the potential to reduce or eliminate the need for exogenous insulin and chronic immunosuppression. The most commonly used biomaterial for this purpose is alginate, a polymer derived from brown algae. A major obstacle to islet transplantation is the lack of adequate islet oxygenation, leading to impaired glucose-responsive insulin secretion [1] and central necrosis [2]. Numerous strategies have been proposed to oxygenate islets in order to prolong the longevity and efficacy of the transplants, but few have been successfully established so far in animal models. The objective of this work was to develop a vascularized islet transplantation device using 3D printing methods and islet immobilization in hydrogels.