(A) A passive pumping tri-channel microfluidic device was fabricated in polydimethylsiloxane (PDMS) (see Bischel et al, Biomaterials 34(5):1471–1477). 1×107 iPSC-ECs / mL were suspended in a PEG monomer and polymerized within the central channel of the device. (B) The PEG hydrogel shear modulus was tuned from 183±10 Pa-1612±95 Pa by maintaining a constant PEG-norbornene concentration while varying the crosslinking density from 40–60% molar ratio thiol:norbornene. (C–H) Maximum intensity projection confocal z-stacks illustrating phalloidin (F-actin, red) and DAPI (nuclei, blue) staining for iPSC-ECs encapsulated in (C,D) 40%, (C,D) 50%, or (C,D) 60% crosslinked PEG hydrogels. Encapsualted iPSC-ECs were cultured in (C,E,G) basal medium (Control, includes 5 ng/mL VEGF) or (D,F,H) basal medium supplemented with 200 ng/mL VEGF (200 VEGF). Scale bars: 250 µm.