Drexel University researchers are trying to expand the possibilities of this system–called transdermal delivery–with the help of a cleverly designed delivery vehicle and an ultrasonic “push,” or pressure from sound waves.

The advantage of transdermal drug delivery is the ability to regulate the release of medication into the bloodstream and promote a more direct interaction of the treatment with the affected area. But the challenge of this method is that the skin is very good at protecting the body from invaders–even the helpful kind.

Molecules of nicotine and medication currently delivered via adhesive patch are small enough to pass through the pores. To sneak a slightly larger package–say, insulin or arthritis medication–past the body’s epidermal defenses requires a bit more biological trickery.

The package

The Drexel team is looking at a drug called Methotrexate (MTX) as an example of the cargo that could one day be transported into the body using an ultrasound “Band-Aid.” MTX is used to treat arthritis and various types of cancer. It is typically taken orally, but after prolonged use it can become toxic to the liver. This side effect could be avoided if the drug were delivered transdermally, as afflicted cells would use up much of the medication before it could reach the liver.

The carrier

Wrenn’s group is designing a vessel that can transport the medicine and penetrate the skin’s first line of defense: the stratum corneum. This barrier is the body’s equivalent of a brick

wall built with dead skin cell bricks and a lipid mortar.

The group selected the liposome, a fabricated lipid sac filled with water, as the carrier. Liposomes are prime candidates for the job because they are made of the same lipid substrate as the stratum corneum’s “mortar,” so they can pass through the skin virtually unnoticed.

The push and the pop

After coaxing the liposomes through the epidermis, the tunable ultrasound patch would “pop” them open to deliver the medicine.

But this interaction is where the real problem lies. The liposome, while a perfect craft for making a stealthy, transdermal entry is not rugged enough to withstand the intensity of ultrasound required to push it through the skin.

Wrenn’s group devised a creative solution to this quandary by adding a bit of ballast to the liposome vessel, in the form of tiny gas-filled sacs called microbubbles.

Microbubbles respond to ultrasound in two ways that are key to making the liposome’s transdermal voyage a success. First, they can be pushed by ultrasound at an intensity gentle enough to keep the liposome intact. So, nesting the microbubbles inside a liposome is analogous to raising the sail on a boat to catch the wind.

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