Engineering three-dimensional microvascular tissues with blood vessel openings for drug transport screening assay

Efficient oxygen and nutrient delivery relies on hierarchical vascular networks formed by the anastomosis of capillaries with larger vessels. However, engineering multiscale microvascular tissues remains a challenge as soft hydrogels tend to promote the formation of dense capillary networks, while rigid scaffolds are required to support anatomically scaled vessels without deformation. Here, we present a three-dimensional, externally accessible microvascular tissue model that integrates self-assembled capillary networks with engineered vessel openings at the gel base. The vessel openings were generated by dissolving thermosensitive poly(2-cyclopropyl-2-oxazoline) microfiber templates, followed by endothelialization and anastomosis with surrounding capillaries. Regardless of gel stiffness, well-defined pore structures were formed, with dimensions corresponding to the microfiber diameter. This strategy overcomes the trade-off between mechanical stability and vascular complexity. The resulting networks exhibited size-selective endothelial transport characteristics, with permeability values dependent on molecular weight, highlighting the potential of this model as a platform for drug transport assays and pharmacokinetic studies.