Disclosed herein is a 3D-printed, biocompatible macroporous device that houses stem cell derived β-cell (SC-β cell) clusters within a degradable fibrin gel. Cluster sizes are used that avoid severe hypoxia within 3D-printed devices and a microwell-based technique is used for resizing clusters within this range. 3D-printed devices may function for at least 12 weeks, are retrievable, and maintain structural integrity.