Researchers from the UK have completed a unique study in 3D printed networks, releasing their findings in the recently published ‘Controlled packing and single-droplet resolution of 3D-printed functional synthetic tissues.’
The development of synthetic tissues requires accuracy in fabricated structures. Currently, while there are challenges in 3D printing such networks, assembly of such geometries can be effective for the performance of specific tasks. In the face of obstacles that often prevent complex designs and necessary functionality, the research team studied how to balance arrangements of droplets brought together with interface bilayers.
Inspired by the 3D polyhedra of nature, the research team examined the properties and performance resulting from molecules packed into crystal structures, as well as cell arrays found in tissues. Their study even included the structure of honeycombs. Such momentum in research is not new as studies have been precipitated by influences such as nacre (found in shells), natural materials like pinecones, and even mammals like bats.
In this study, the researchers experimented with fabrication concepts bordering on the 4D printing level as they considered how to improve control over deformable ‘spheres,’ allowing them to imitate live tissue.
“In this area, networks of picolitre-sized droplets separated by droplet interface bilayers (DIBs) hold significant promise because of discrete compartmentalization, inherent connectivity, and communication between subunits,” stated the researchers.
Strengthened by the presence of lipids, DIBs are built as aqueous droplets connect in oil and create a bilayer, with networks being created through microfluidics, mechanical manipulation, magnetism, and optical tweezers.
“When aqueous droplets pack in 3D, each makes multiple droplet–droplet contacts (by forming DIBs with its neighbors), resulting in the deformation of the spherical droplets into polyhedral,” stated the researchers.
The science of building such networks does require thorough comprehension of how printing parameters affect droplet deformation:
“At present, for example, the occurrence of printing defects dictates that conductive signaling pathways in large networks (>100 droplets) must be designed to be more than 2–3 droplets wide to ensure continuity,” stated the researchers. “However, single-droplet-wide signaling pathways would be feasible if synthetic tissues could be patterned at single-droplet resolution.”
Previously, researchers have explored deformation of droplets in oil and water mixtures, including the fabrication of microfluidic systems for experimenting with drops in 2D sheets—as well as studying clusters that self-organize while flowing. Noted as most helpful to their own research, studies by Princen et al. focused on the value of contact angles between droplet packing in both 2D and 3D. In this study, the researchers experimented with hexagonal close-packed (hcp) lattices from hundreds of 3D-printed picolitre-sized droplets, as well as using automation to fabricate synthetic tissues with single droplets.
Using a 3D printer built in their own lab, the researchers explored structures via 3D droplet networks with hundreds of droplets included (PBS, 100 µm diameter, ≈524 pL volume). Each network required 224 droplets at droplet ejection frequency of 0.5 s−1. Overall, 129 printed networks were evaluated, resulting in two major arrangements: hexagonal close-packed (hcp) and body-centre cubic (bcc). They also categorized irregular packing as either ‘amorphous’ or ‘not packed.’
Results offered three θDIB-dependent situations:
- θDIB << θc, droplet networks pack loosely with the greatest amount of no packing
- θDIB >> θc, droplet networks pack tightly and are distorted, with the greatest amount of amorphous packing
- θDIB ≈ θc, droplet networks show the greatest amount of hexagonal packing
With 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) added to the lipids, contact angle equilibration was rapid initially, but followed by a slower phase. The study confirmed that:
“… the regularity of the hcp in 3D-printed droplet networks was optimal when θDIB ≈ θc, and also when the printing frequency and the kinetics of DIB formation were matched to allow the initial formation of regular 2D hexagonal packing in the first layer, which then templated hcp when subsequent layers were printed on top.”
For hcp regions, space-filling trapezo-rhombic dodecahedra were formed, consisting of 12 DIBs and peripheral droplets.
“Our findings are applicable to any other assemblies of compartmentalized systems—such as adhesive giant uni-lamellar vesicles or protein compartments—in which structural order is required to build synthetic tissues with precise functionalities,” concluded the research team, confirming that they can 3D print droplet networks with complex designs, and at high resolution—like tubular structures.
“This level of precision was not achieved at the periphery of the 3D printed constructs, where most printing defects and irregular arrangements of droplets were confined. However, our observations also suggest that regular packing at the periphery of 3D-printed droplet networks might be further improved by ‘annealing’ steps after the printing process (i.e., cyclical decrease and increase in contact angles), or by templating the droplet packing lattice using patterned surfaces.”
What do you think of this news? Let us know your thoughts! Join the discussion of this and other 3D printing topics at 3DPrintBoard.com.[Source / Images: ‘Controlled packing and single-droplet resolution of 3D-printed functional synthetic tissues’]
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