Sterilizing with Sound: Acoustic Technique Offers Improved Medical Disinfection

Preliminary studies by scientists at the Georgia Institute of Technology and Georgia State University showed the technique killed more than 90 percent of bacteria in a test vial that also contained a mild solution of isopropyl alcohol. Results of the work were presented December 5 at the First Pan-American/Iberian Meeting on Acoustics in Cancun, Mexico.

"Complex and extremely expensive endoscopes and related surgical equipment are very vulnerable to heat, and they are challenging to clean," explained Dr. Stephen Carter, an Atlanta-area dentist who is working with Georgia Tech Professor Kenneth Cunefare to develop the technique. "We believe that our methods will sterilize in shorter periods of time, which would be a substantial advantage for expensive medical equipment."

The patented technique uses a form of cavitation, a phenomenon in which acoustic energy applied to a liquid induces the creation of voids -- or bubbles -- that release energy when they collapse. By pressurizing their test chamber while inducing cavitation, Cunefare and Carter create a form of transient cavitation that causes violent collapse of the bubbles.

The enhanced cavitation takes advantage of the "anomalous depth effect," in which the impact of bubble collapse increases dramatically when subjected to roughly twice normal atmospheric pressure. Scientists have studied the phenomenon for years because it can damage submarines' propellers when operating at certain depths.

When applied to a solution of 66 percent isopropyl alcohol containing two forms of "marker" bacterial spores -- Bacillus stearothermophilus and Bacillus subtilis -- the enhanced cavitation reduced the bacterial count by more than 90 percent, Cunefare said. Research indicates that both the alcohol solution and increased pressure are necessary for killing the spores with cavitation.

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