Microfluidic systems including a housing configured to receive a cartridge, the cartridge including a plurality of wells for receiving one or more biological cells are described herein. The microfluidic systems include a structure with channels for introducing a medium into the housing and through channels the cartridge. Microfluidic systems including a housing configured to receive a cartridge, the housing including channels for loading one or more biological cells within wells of the cartridge are described herein. Three-dimensional scaffolds, devices, and systems comprising such scaffolds that mimic the in vivo structure, physical properties, and protein composition of extracellular matrix surrounding pancreatic islet cells and adipocytes, and the use of such compositions, devices and systems for, e.g., in vitro drug screening and/or toxicity assays, disease modeling, and therapeutic applications are also described herein.