A new and simple way to control the stickiness of medical adhesives using ultrasound eliminates the need to use any potentially toxic chemicals to increase bioadhesion. The technique, developed by researchers from McGill University in Canada and ETH Zurich in Switzerland, could prove invaluable for applications such as tissue repair, wound healing, wearable electronics and drug delivery.
Bandages and plasters don’t usually stick well to wet skin. Ultrasound could help overcome this problem, not only on skin but on many other tissues, including mucosal membranes and aorta, explains lead author Zhenwei Ma, now at Harvard University and the University of British Columbia.
In their work, the researchers used microbubbles induced by low-frequency ultrasound to make adhesives stickier. The waves locally “boil” the liquid in an adhesive primer spread on the tissue substrate (a solution containing chitosan, gelatine or cellulose), forming vapour bubbles that grow and collapse violently towards the tissue surface. “Hydrogel patches made of polyacrylamide or poly(N-isopropylacrylamide) combined with alginate were then applied to the treated region to achieve strong adhesion,” explains Ma.
“This motion results in mechanical interactions that transiently push the adhesives into the skin and other tissues for stronger bioadhesion,” Ma tells Physics World. “By simply adjusting the intensity of the ultrasound and manoeuvring the ultrasound probe used to create the bubbles, we can control – very precisely – the stickiness of the adhesive bandages.”
The researchers tested their technique on rat and pig tissue. They found that the ultrasound amplified the adhesion energy between the tissue and the hydrogel by up to 100 times, and increased the interfacial fatigue threshold between the two by 10 times. Indeed, they measured adhesion energies of over 2000 J/m2 for skin, around 295 J/m2 for buccal mucosa and around 297 J/m2 for aorta. In comparison, adhesion energies for hydrogels not subjected to ultrasound were approximately 50, 12 and 17 J/m2, respectively.
Ultrasound-induced cavitation
The team’s theoretical modelling calculations suggest that the main mechanism underlying this bioadhesion is ultrasound-induced cavitation, which propels and immobilizes anchoring primers into tissue. It is the mechanical interlocking and interpenetration of these anchors that ultimately produces strong adhesion between hydrogel and tissue without the need for chemical bonding.
Ultrasound sticker provides continuous imaging of internal organs
The adhesives could also be used to deliver drugs through the skin. “This paradigm-shifting technology will have great implications in many branches of medicine,” says Ma. “We’re very excited to translate this technology for applications in clinics for tissue repair, cancer therapy and precision medicine.”
As well as the unprecedented controllability of bioadhesion strength, the researchers say that their technique will allow many more types of materials to be used as bandages, plasters and interfaces with biological tissue. This will inevitably expand the potential areas of application, they say.
The researchers report their work in Science.
