Abstract
3D-printing networks of droplets connected by interface bilayers are a powerful platform to build synthetic tissues in which functionality relies on precisely ordered structures. However, the structural precision and consistency in assembling these structures is currently limited, which restricts intricate designs and the complexity of functions performed by synthetic tissues. Here, we report that the equilibrium contact angle (θDIB) between a pair of droplets is a key parameter that dictates the tessellation and precise positioning of hundreds of picolitre-sized droplets within 3D-printed, multi-layer networks. When θDIB approximates the geometrically-derived critical angle (θc) of 35.3°, the resulting networks of droplets arrange in regular hexagonal close-packed (hcp) lattices with the least fraction of defects. With this improved control over droplet packing, we can 3D-print functional synthetic tissues with single-droplet-wide conductive pathways. Our new insights into 3D droplet packing permit the fabrication of complex synthetic tissues, where precisely positioned compartments perform coordinated tasks.
Highlights
3D-printing networks of droplets connected by interface bilayers are a powerful platform to build synthetic tissues in which functionality relies on precisely ordered structures
We found that θDIB is directly proportional to both φSIL (Fig. 1b–d, f) and xPOPC (Fig. 1g), and that the maximum value of θDIB of 90° was approached at φSIL = 0.65 and xPOPC = 1.00 (Fig. 1e)
We find that hcp is maximised in 3D-printed droplet networks when θDIB ≈ θc because, at this contact angle, the tetrahedral arrangements of droplets[30] are maintained in the position imposed by the printing nozzle with minimal distortions
Summary
3D-printing networks of droplets connected by interface bilayers are a powerful platform to build synthetic tissues in which functionality relies on precisely ordered structures. The packing of space-filling polyhedra in three dimensions (3D) is a common theme in nature, from the atomic packing of molecules in crystal structures[1], to the regular arrays of cells in tissues[2], to the macroscopic tessellation of honeycombs created by bees[3] In these examples, distinctive properties and precise functions arise from controlled arrangement and patterning of their subunits. The controlled close packing of deformable spheres is critical for fabricating synthetic tissues that are designed to mimic the complex and cooperative structures and functions of living tissues In this area, networks of picolitre-sized droplets separated by droplet interface bilayers (DIBs) hold significant promise because of discrete compartmentalisation, inherent connectivity and communication between subunits[4,5,6]. Single-dropletwide signalling pathways would be feasible if synthetic tissues could be patterned at single-droplet resolution
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