How levitating droplets can increase drug effectiveness

Developed for NASA to simulate microgravity conditions, an acoustic levitator defies gravity, suspending liquid drugs mid-air. The method could make HIV drugs more effective. With video.

Sound waves can keep liquid drops suspended in the air, defying gravity for long periods of time.

And now scientists at the U.S. Department of Energy’s (DOE) Argonne National Laboratory have discovered a way to use sound waves to levitate individual droplets of solutions containing different pharmaceuticals – in hopes of developing more effective drugs with fewer side effects.

“One of the biggest challenges when it comes to drug development is in reducing the amount of the drug needed to attain the therapeutic benefit, whatever it is,” says Argonne’s Chris Benmore.

At the molecular level, pharmaceutical structures fall into one of 2 categories: amorphous or crystalline. According to an Argonne news release:

Amorphous drugs typically are more efficiently taken up by the body than their crystalline cousins; this is because amorphous drugs are both more highly soluble and have a higher bioavailability, suggesting that a lower dose can produce the desired effect.

Most drugs on the market are crystalline, but because they don’t get fully absorbed by the body, we not getting the most efficient use out of them. However, getting drugs into an amorphous state isn’t easy: if the solution evaporates while in contact with part of a vessel where it’s stored, it’s far more likely to solidify in its crystalline form.

So, how do you evaporate a solution without it touching anything?

Since the vibrational force of sound waves can keep drops of solution stationary in a column of air, they turned to an acoustic levitator – a piece of equipment originally developed for NASA to simulate microgravity conditions.

Levitation or ‘containerless processing’ can form pristine samples that can be probed with the high-energy X-ray beam, making it possible to study the amorphization of drugs.

  • Two small speakers generate sound waves at frequencies slightly above the audible range (roughly 22 kilohertz).
  • When aligned, the top and bottom speakers create two sets of sound waves that interfere with each other, creating a standing wave.
  • At certain points along a standing wave (called nodes), there is no net transfer of energy at all.
  • Because the acoustic pressure from the sound waves cancel the effect of gravity, light objects are able to levitate when placed at these nodes.

Watch a video of levitating droplets here.

The team has used the acoustic levitator to amorphize HIV drugs Ritonavir and Efavirenz, TPM reports. Benmore says they’re “already 90% effective… by making the drugs in glassy form more of the drug is absorbed by the body and the side effects (stomach cramps) are minimized.”

They’ve investigated over a dozen other pharmaceuticals, and a patent for the method is being pursued.

Images: Dan Harris / Argonne National Laboratory

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