Fig. 1. Schematic illustration of a 3D microvascular system formed by mechanically guided assembly.

A double-layer 3D microvascular network, with an enclosed internal cavity between the top and bottom layers, features a stepwise change in the width of the microchannels (from 100 μm, to 30 μm, to 10 μm, and then back to 30 μm and 100 μm) and a three-level branching structure. The narrowest microfluidic channel branches have widths of 10 μm, comparable to the sizes of capillaries in human vasculature. (A and B) Optical images and FEA predictions [with rendering in (A)] of the spheroid-shaped 3D microvascular network from a 3D view (A) and an approximate side view (B). (C) Magnified view of the blue dashed rectangle in (B). (D) Schematic illustration showing the selective locations to bond the microfluidic double layers to a prestretched elastomer substrate. (E) Procedures to fabricate 2D precursors of the microvascular network. Scale bars, 5 mm (A and B) and 2 mm (C). Photo credit: H. Luan, Northwestern University.