Microscale platform for studies of human stem cells. The platform was designed using a 3D CAD software with the following design criteria: (i) Capability of generating multiple concentration gradients in a no-shear environment, (ii) 3D culture of EBs, (iii) high-throughput, (iv) compatibility with online imaging, (v) easy retrieval of the EBs for additional analyses. The platform comprises a matrix of conical microwells accommodating EBs while shielding them from shear forces. The integrated microfluidic platform generates concentration gradients across the rows of microwells. The overall dimensions of the device are comparable to a standard microscope slide. Multiple prototypes with varying numbers of microwells were made; a prototype with five microwells per row is shown. (a) From the CAD file a mold was produced via Stereolithography Rapid Prototyping. (b) The mold could be used indefinitely to produce replicates of the microbioreactor via replica molding in poly(dimethylsiloxane). (c) A dye-tracer fluid fills the device, for visualization of the channels and microwells. (A color version of this figure is available in the online journal.)