Phototunable hydrogel mechanics for spatial guidance of blood capillary morphogenesis.

Creating large, functional tissue requires the engineering of a blood capillary network, which is challenging as it necessitates the recapitulation of capillary morphology and spatial distribution. Current approaches employ local mechanical and chemical gradients to modulate capillary morphology or the network's density but they often fail to regulate both parameters to fulfill the needs of tissue engineering. Here, we present a light-mediated biomaterial platform based on the FLight biofabrication technique to regulate blood capillary alignment and density. By modulating local light doses, a highly aligned hydrogel microstructure with spatially tunable matrix stiffness was achieved within a single 3D hydrogel construct. The anisotropic microstructures guided blood capillary elongation and alignment, achieving over 90% alignment in matrices (3.4-5.4 kPa), while spatial variations in stiffness regulated vascularization. Blood capillary density was maximized in regions with intermediate stiffness (4.6-5.0 kPa) and markedly lower in softer (∼2.0 kPa) and stiffer (∼5.4 kPa) matrices. This study establishes spatial light dosage as an effective engineering parameter for programming matrix mechanics and microvascular organization within a single hydrogel construct, providing a scalable strategy for fabricating anisotropic and spatially heterogeneous capillary networks for vascularized tissue engineering.