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uWAMIT researchers have discovered that ultrasound applied to therapeutic liquid solutions creates foams with smaller bubbles and a more uniform size distribution than traditional mechanical agitation methods. This technique may yield safer and more effective foam sclerosis treatments. |
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What is Sclerotherapy? |
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Sclerotherapy is a procedure to treat varicose veins. Treatment commonly involves the injection of a sclerosing agent directly into the pathological vein through a small needle. The agent damages the endothelial lining of the vessel and causes an inflammatory reaction. A small fibrous cord eventually replaces the vein — this process is known as sclerosis. |
Treatment is most effective in small veins, about 3 mm or less in diameter. Efficacy decreases in larger vessels because the sclerosing agent in solution is diluted by blood and ultimately transported away from the injection site. For many years now, physicians have overcome this limit by transforming the therapeutic solution into a foam. |
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Foam Properties |
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When the therapeutic agent is suspended in a foam, the foam itself displaces the intravascular blood mechanically, maximizing the contact of the sclerosing agent with the endothelial wall. This mechanical assist also means that lower concentrations and volumes of sclerosing agent are required for treatment. |
Foam therapies have been related to serious adverse events. Neurological complications can occur if relatively large gas bubble enter the cerebral districts and obstruct normal blood flow. Because large bubbles may be a complicating factor, we are seeking to develop foams with smaller bubble size distributions. |
Optical image of small, uniformly sized bubbles in a foam produced by 20-kHz ultrasound. |
Optical image of bubbles in a foam produced by mechanical agitation. |
Optical image of small bubbles in a foam produced by the Tessari technique. |
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Ultrasonic Preparation of Foams |
How Does Ultrasound Make Foam? |
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Sclerosing foams are gas bubbles trapped in a liquid network stabilized by surfactants. The evolve irreversibly over time through drainage, coalescence of bubbles, and gas diffusion from small to large bubbles. We hypothesize that sclerotherapy is safer and more effective the smaller the bubbles and the more uniform the bubble size distribution. Foam stablity is enhanced by smaller bubbles because of the higher density network of channels inside the foams. |
We are investigating the use of low-frequency ultrasound (20 kHz) to optimize foam preparation as an alternative to mechanical agitation methods. Initial studies show that sclerosing agent solutions prepared by sonication have the smallest bubbles, nearly twice as small as other preparation methods. Ultrasound also produces foams with a uniform bubble size distribution and the smallest maximum size bubbles. |
When low-frequency ultrasound of sufficient amplitude passes through the liquid, small cavitation bubbles are formed. These bubbles get coated with surfactants that stabilize the bubbles and prevent them from dissolving. The coating also prevents them from coalescing into larger bubbles. The net result is a distribution of small bubbles. |
