How can three liquids remain separate while becoming one microscopic droplet? MIT researchers built a compact electrospray array that guides three non-mixing liquids through concentric nozzles. In tests, its 16 emitters generated uniform droplets with an outer layer, a middle layer, and a core.
The demonstrated result is a fabrication and droplet-generation system. Drug delivery, self-healing materials, biosensors, and artificial cells are proposed applications of the layered particles.
High voltage produces a stream of microdroplets
An electrospray emitter applies high voltage to liquid as it exits a nozzle, producing a steady stream of extremely small droplets. A single emitter has modest output, so an array is needed to increase production without losing uniformity.
Each triaxial emitter contains three concentric nozzles. Three immiscible liquids flow through them simultaneously to form distinct layers in each droplet. The resulting multilayer droplets can solidify into particles with distinct layers.
Coiled channels supply 16 emitters evenly
The array is slightly larger than a U.S. penny and places 16 nozzles in about one square centimeter. Inside, a network of helical microchannels carries liquid to each emitter. This geometry helps maintain uniform spraying while keeping the device compact and limiting interference among neighboring emitters.
Uniformity also depends on alignment. The three concentric nozzles must line up precisely to emit consistent layered droplets. The researchers had to print the tiny channels without support structures that could clog them and remove all uncured resin before operating the device.
Vat photopolymerization creates the internal geometry
The team used vat photopolymerization, which solidifies thin layers of liquid resin with light. They printed layers 25 micrometers tall, enabling the intricate three-dimensional channels and concentric nozzle geometry. The 25-micrometer value describes print-layer height, not droplet diameter.
The one-step fabrication process produced the complex emitter arrays in a few hours. That duration refers to manufacturing the device, not producing an individual droplet.
The middle liquid controls layer stability
The researchers tested several architectures and combinations of liquid flow rates. The viscosity of the middle liquid had the largest role in droplet stability because it preserved the thickness of each layer.
Adjusting flow rates and voltages also changed the thickness of individual droplet layers. This could allow scientists to design drug-delivery particles with layers tailored so medicine releases at the intended time.
The printed array generated uniform three-layer droplets across its emitters. Future work aims to reduce device dimensions further and integrate conductive or dielectric materials. The present advance is the combination of printable microchannels, aligned concentric nozzles, and controlled liquid conditions that lets a compact 16-emitter array produce consistent layered droplets.
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