HA-hydrogel synthesis and study strategy. (A) Schematic of AHA hydrogels. AHA hydrogels are formed by reacting AHA molecules with RGD-containing peptides and encapsulating soluble growth factors (GFs; i). ECFCs and MMP-sensitive crosslinkers are then added to form the constructs (ii). (B) Schematic of vascular morphogenesis activation strategy at each stage during culture of AHA hydrogels. In response to RGD and soluble GFs, encapsulated ECFCs undergo vacuole formation, the first initial step in vascular morphogenesis. Vacuolated ECFCs then merge with the neighboring cells to form an open lumen compartment (i-ii). MMP-sensitive crosslinkers subsequently enable ECFC tubulogenesis to progress through both branching and sprouting, to form complex and comprehensive vascular networks (iii-iv).