Canadian researchers have found that they can effectively stick hydrogel pads into the skin using ultrasound waves. ETH Zurich professor Outi Supponen has now explained the basic mechanism: creating bubbles inside the adhesive between the plaster and the skin anchor.
Ultrasound may be used to secure the gel pad to the skin. Image credit: Ran Huo & Jianyu Li, McGill University
Today, hydrogel patches are commonly used in wound care and to attach wearable electronic devices to the skin. But these patches don’t stick to the skin particularly strongly, especially if the skin is wet.
A team of Canadian researchers led by Jianyu Li of McGill University has found that these patches can be very firmly and permanently attached to the skin using ultrasonic waves. Furthermore, by varying the intensity of the ultrasound waves, the researchers were able to precisely control how firmly the hydrogel rubber pads adhere to the skin and other tissues.
In tests on pig skin, the bonding of the ultrasonic patches was up to 100 times stronger than that of the non-ultrasonic patches. The researchers also achieved a bond that was 10 times stronger when the patches were applied to the skin of live mice.
But exactly why ultrasound helps achieve such a strong bond is a mystery to Canadian researchers – a mystery that has now been addressed by Outi Supponen, Professor of Multiphase Fluid Dynamics at ETH Zurich , and postdoctoral researcher Claire Bourquard partially answered. The study, conducted by two research groups, was recently published in the journal Science.
The gap helps the plaster to adhere better
Gel patches adhere very well because applying ultrasonic waves creates special bubbles, called foam bubbles, in the adhesive on the underside of the hydrogel. The greater the ultrasonic intensity, the larger the number and size of the bubbles. These bubbles then instantly explode, causing each bubble to transform within milliseconds into a tiny jet that shoots toward the surface of the skin, where they slam the molecular components of the adhesive into the layer. cuticle like a jackhammer. This is how the plaster is fastened. “The principle behind this strong bond is cavitation – a purely mechanical process,” says Supponen.
What scientists mean by cavitation is the formation and collapse of vapor-filled bubbles in a liquid. When the bubbles burst, they release a large amount of energy. For example, cavitation occurs around very fast moving objects in liquids – such as the propulsion of ships or the turbines of hydroelectric power plants. Since the energy released when the bubble collapses can severely damage these objects, cavitation should be avoided as much as possible in these applications.
“If we can learn to apply cavitation energy in a controlled manner, we can use it to our advantage,” says Supponen. She added that tests on mice showed that applying the hydrogel patch with ultrasonic waves was harmless. “The ultrasonic cavitation in the adhesive does not damage the animal’s skin at all.”
Possible applications for ultrasound “bond engineering” include patches for vaccines, cancer drugs, or insulin through the skin.
Source: ETH Zurich
