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Energy-Efficient Process Devised for Nano-Emulsions

Water drops

(Arek Socha, Pixabay)

21 June 2019. A more efficient process using less energy is being developed for producing emulsions with tiny droplets to deliver drugs or cosmetics through the skin. Researchers from Massachusetts Institute of Technology and cosmetics company L’Oréal in Paris that funded the research describe their process in today’s issue of the journal Nature Communications.

A team led by MIT chemical engineering professor Patrick Doyle is seeking a better process for creating emulsions with nanoscale droplets suspended in a carrier liquid, much like salad dressing with oil and vinegar. The smaller the droplets — in this case no more than 200 nanometers, where 1 nanometer equals 1 billionth of a meter — the more stable they become, allowing for longer storage times. And smaller emulsion droplets better penetrate the skin, for drugs and cosmetics, as well as mucus membranes in the nose for nasal sprays.

Creating emulsions with these fine droplets using today’s technologies, however, requires considerable energy expenditures. Doyle and colleagues aimed to produce ultra-fine emulsions with more a efficient process requiring much less energy. In addition, the researchers sought to produce emulsions that could turn to a gel when in contact with the skin to reduce waste when applied. And the researchers needed to use materials already approved by the Food and Drug Administration to meet safety requirements.

Doyle’s lab studies physical properties of soft matter, particularly in micro- and nanoscale formulations. Producing an emulsion at that fine scale usually requires surfactants to help speed the emulsifying process. Surfactants are substances that reduce the surface tension of liquids in a solution making them more slippery, but many commercial surfactants have ingredients that cause skin irritation. The researchers found two surfactants already approved by FDA and used in consumer products: polysorbate and sorbitan oleate. The team also added the common biocompatible polymer polyethylene glycol to further reduce the droplet size to about 50 nanometers.

The team discovered that this combination of emulsifiers and surfactants makes it possible to produce nanoscale droplets of isopropyl myristate, the “oil” part of its emulsion, much more efficiently than before. “With this approach, you don’t have to put in much energy at all,” says Doyle in an MIT statement. “In fact, a slow stirring bar almost spontaneously creates these super small emulsions.”

The researchers then turned to formulating the emulsion in a heat-sensitive gel. Their solution aimed to produce a hydrogel, a water-based polymer material, with a type of polymer known as Pluronics. This polymer is made of three chemical segments, two parts that attract water on the outside of its molecules, and a water-repelling part on the inside. When heated, the water-repelling parts of Pluronics attach to the oil droplets, which forces the droplets more tightly together. This action turns the liquid suspension into a a more solid gel material.

The team demonstrated the emulsion-gel to deliver the over-the-counter pain medication ibuprofen. The researchers show a nanoscale emulsion with ibuprofen could form into a gel at a human’s body temperature of 37 degrees C, and release the ibuprofen in about 30 minutes. The team also show emulsion-gel’s heat reactivity can be adjusted by varying droplet size and Pluronics concentrations, with a gel forming at 10 degrees C (50 F) and releasing ibuprofen in about 10 minutes.

Doyle’s lab is looking into tests of the gel with a range of different drug ingredients, both for topical delivery and inside the body. For cosmetics, the nanoscale emulsions could be used for skin creams and moisturizers with a longer shelf life.

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