MIT scientists have devised a low-cost method for crafting specialized electronic nozzles known as triaxial electrospray emitters. These devices could efficiently produce time-release drug-delivery particles or self-healing materials on a large scale. Triaxial electrospray emitters use electricity to precisely dispense three liquids from tiny nozzles, creating a continuous stream with three separate fluid layers. The resulting multilayered droplets can solidify into layered microparticles.<\/p>\n
For example, a series of triaxial electrospray emitters can generate three-layer drug-delivery nanoparticles. The outermost layer might gradually dissolve in the stomach, revealing a secondary material that manages the release of the core substance, targeting a specific area in the intestines. Traditionally, creating an array of electrospray emitters involves costly and time-intensive microfabrication in semiconductor cleanrooms, limiting their application. MIT researchers addressed these challenges by 3D-printing arrays of triaxial electrospray emitters, featuring 16 nozzles within roughly one square centimeter. Each device includes a complex network of three-dimensional microchannels to uniformly supply liquid to the nozzles.<\/p>\n
Their single-step fabrication process produces complex emitter arrays in only a few hours. Upon testing, the 3D-printed arrays consistently generated three-layered droplets on a large scale. Uniformity is crucial for high-throughput production of layered microparticles, which have applications in biosensors for detecting chemicals or artificial cells for tissue regeneration. “We couldn\u2019t make a device like this in a semiconductor cleanroom. This is only possible because they are 3D-printed,” says Luis Fernando Vel\u00e1squez-Garc\u00eda, a principal research scientist at MIT’s Microsystems Technology Laboratories and senior author of a paper on this development. “The particles these devices generate, whether they are used for a self-healing composite or to deliver medicine, can have a big impact in many applications. We want to democratize this technology so the benefits can touch many more people.”<\/p>\n
Vel\u00e1squez-Garc\u00eda co-authored the paper with Bryan Ivan Quintanar-Abarca from the Technological Institute of Monterrey in Mexico, and the research is published in Virtual and Physical Prototyping. Electrospray emitters apply high voltage to a liquid as it exits the nozzle, creating a steady flow of tiny droplets. Triaxial devices have arrays of three concentric nozzles that emit three non-mixable liquids into layered droplets, producing compound microparticles with distinct layers. For instance, a triaxial electrospray emitter could create a biosensing particle with three chemical markers, one in each layer, and can produce smaller microdroplets much faster than other techniques.<\/p>\n
Miniaturization is crucial for electrospray devices as smaller emitters require less voltage to produce droplets. Individual electrospray emitters have modest output, so arrays are necessary to increase droplet production while maintaining uniformity. Multi-emitter electrospray devices are usually made in semiconductor cleanrooms, but traditional methods limit possible shapes and sizes. The researchers found no previous reports of a miniaturized triaxial electrospray array, underscoring the novelty of this work. “When you build a triaxial array, you need to find a way to create geometries that have many integrated parts and extremely fine structures in the smallest footprint possible. And you need to ensure the devices will work uniformly,” Vel\u00e1squez-Garc\u00eda explains.<\/p>\n
To achieve this, they employed a 3D-printing technique called vat photopolymerization, which uses light to solidify thin layers of liquid resin, building a complex device layer by layer. This precise method allowed the researchers to print layers only 25 micrometers tall, a fraction of a human hair’s width, enabling the intricate internal design necessary for a triaxial electrospray emitter. The array, slightly larger than a U.S. penny, contains internal coiled channels that deliver liquid to 16 nozzles. These helical microchannels ensure a uniform spray of microdroplets across all nozzles while maintaining a compact device size.<\/p>\n
“In a sense, the emitters in the array never learn they have company, or otherwise there would be cross-talking and causing interference between them. We achieved uniformity because of the work that went into our designs,” Vel\u00e1squez-Garc\u00eda says. They also had to create extremely small channels without support structures, which could block the device, and ensure all uncured resin was removed before use. The microchannels direct liquid to the concentric nozzles, which must be perfectly aligned for consistent microdroplet emission.<\/p>\n
“We were able to aggressively optimize the design because we could iterate in a much timelier manner. This ability to exquisitely refine designs is a key advantage of 3D printing,” Vel\u00e1squez-Garc\u00eda says. The researchers tested various architectures to find the best liquid flow rates for stable, consistent microdroplet emission. Surprisingly, they discovered that the middle liquid’s viscosity is crucial for maintaining microdroplet stability, as it preserves layer thickness. Moreover, by adjusting flow rates and voltages, they could precisely control the thickness of each microdroplet layer, allowing the design of drug-delivery particles with ideal layers for timed medicine release.<\/p>\n
“By making such intricate devices more practical, we can empower others to pursue entrepreneurial and scientific advances,” Vel\u00e1squez-Garc\u00eda says. Looking ahead, the researchers plan to refine their fabrication process and designs further to achieve even smaller dimensions and incorporate conductive or dielectric materials into the devices for more advanced electrospray emitter arrays. This research received funding from the Tecnol\u00f3gico de Monterrey \u2013 MIT Nanotechnology Program.<\/p>\n