Strong adhesion thanks to cavitation bubbles

Today, hydrogel dressings are often used to heal wounds and to secure portable electronic devices to the skin. But these dressings do not adhere particularly strongly to the skin, especially if the skin is moist.

A team of Canadian researchers led by Jianyu Li of McGill University has just discovered that these dressings can be fixed very firmly and durably on the skin thanks to ultrasound. Additionally, by varying the intensity of the ultrasound waves, researchers can precisely control the strength with which hydrogel dressings adhere to skin and other tissues.

In tests on pigskin, the adhesion of dressings applied with ultrasound was up to 100 times stronger than that of dressings applied without ultrasound. The researchers also obtained a ten times stronger bond when applying the dressings to the skin of live rats.

But precisely why ultrasound helps make such strong connections was a mystery to Canadian researchers – a mystery that has now been partially solved by Outi Supponen, professor of multiphase fluid dynamics at ETH Zurich, and his postdoctoral researcher Claire Bourquard. The study by the two research groups was recently published in the journal Science.

Cavitation allows better adhesion of the plaster

The reason gel dressings adhere so well is that applying ultrasound creates special bubbles, called cavitation bubbles, in the adhesive on the underside of the hydrogel. The greater the ultrasound intensity, the greater the number and size of the bubbles. These bubbles then immediately implode, each transforming within milliseconds into a mini-jet that shoots towards the surface of the skin, where they drive the molecular components of the adhesive into the epidermis like a jackhammer. This is how the plaster sets firmly. “The principle behind this strong bond is cavitation – a purely mechanical process,” says Supponen.