Nanoemulsion Gels Are a New Way to Deliver Drugs Through the Skin

Researchers at MIT have developed a novel way to deliver medication through the skin using nanoemulsions, or mixtures of liquids suspended within each other.

Researchers have been devising numerous new ways to deliver medications and other therapies more directly to patients to make it less invasive and more targeted for specific ailments and diseases.

MIT chemical engineers have come up with one of the latest of those with the development of what are called nanoemulsions that can be used to create materials to deliver medication that can be absorbed by or injected into the skin.

nanoemulsions, gels, MIT, small molecule therapeutics, biocompatible polymer
MIT chemical engineers have devised a way to convert liquid nanoemulsions into solid gels. These gels (shown in red) form almost instantaneously when drops of the liquid emulsion enter warm water. (Image Source: MIT and the researchers)

Nanoemulsions are very tiny droplets of a liquid suspended within another, similar to the mixture formed when one shakes a bottle of salad dressing of vinegar and oil, researchers said.

A team led by Patrick Doyle, a professor of chemical engineering at MIT, discovered how to convert liquid nanoemulsions to a gel when they reach body temperature--98.6 degrees Fahrenheit or 37 degrees Celsius. He and his team said this discovery could be useful for developing materials that can deliver medication when rubbed on the skin or injected into the body.

“The pharmaceutical industry is hugely interested in nanoemulsions as a way of delivering small molecule therapeutics,” he said in a press statement. “That could be topically, through ingestion, or by spraying into the nose, because once you start getting into the size range of hundreds of nanometers, you can permeate much more effectively into the skin.”

Less Energy, Same Stability

A simple way to create an emulsion is to add energy, such as in the example of shaking salad dressing. The drops in the emulsion become smaller and more stable if more energy is used.

Nanoemulsions are some of the most stable of these type of liquid mixtures, with droplets that have diameters of 200 nanometers or smaller, researchers said. They also can carry larger payloads—i.e., medications or sunscreens, for example—because they have a higher ratio of surface area to volume, researchers said.

Doyle and the researchers in his lab have been develop strategies for the past few years to create nanoemulsions with less energy than they typically need. This could help adapt these technologies for large-scale industrial manufacturing, researchers said.

Detergent-like chemicals called surfactants can speed up the formation of emulsions, researchers said. However, many of the surfactants that have previously been used for creating nanoemulsions are not FDA-approved for use in humans.

Doyle and his students chose two surfactants that are uncharged, which makes them less likely to irritate the skin, and are already FDA-approved as food or cosmetic additives. They also added a small amount of polyethylene glycol (PEG), a biocompatible polymer used for drug delivery that helps the solution to form even smaller droplets, down to about 50 nanometers in diameter.

“With this approach, you don’t have to put in much energy at all,” Doyle said. “In fact, a slow-stirring bar almost spontaneously creates these super small emulsions.”

Active ingredients can be mixed into the oil phase before the emulsion is formed, so they end up loaded into the droplets of the emulsion, he added.

From Emulsion to Gel

Once they had developed a low-energy way to create nanoemulsions using nontoxic ingredients, the researchers added a step that would allow the emulsions to be easily converted to gels when they reach body temperature, they said. They achieved this by incorporating heat-sensitive, tri-block polymers called poloxamers, or Pluronics, which are already FDA-approved and used in some drugs and cosmetics, Doyle said in the press statement. Their molecular structure and characteristics allow for the transformation to happen, he said.

Researchers describe their work in a paper in the journal Nature Communications.

To demonstrate their work, researchers created nanoemulsions that remained stable for more than a year, they report in the paper. They also incorporated ibuprofen into the solutions to show that medications could indeed be delivered in this way.

Researchers now are turning their attention to how to incorporate active pharmaceutical ingredients into the gels they created from the nanoemulsions. They believe these gels could be useful for topical medications, such as those applied to heal burns or other injuries of the skin, or cosmetic uses.

Elizabeth Montalbano is a freelance writer who has written about technology and culture for more than 20 years. She has lived and worked as a professional journalist in Phoenix, San Francisco and New York City. In her free time she enjoys surfing, traveling, music, yoga and cooking. She currently resides in a village on the southwest coast of Portugal.

 

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