Medical hopes for on-off adhesive developed at university

The material loses and regains its stickiness when the acidity around it alters.

Scientists believe it could have important medical applications, with the body’s natural acidity acting as a trigger for releasing drugs.

The technology could also be useful in the design and control of micro-sized nanomachines.

The glue is made of molecular chains called polyelectrolytes, which are electrically charged and change shape in response to their environment.

A polyelectrolyte can stretch out at one acidity level and roll into a ball at another.

Researchers led by Dr Mark Geoghegan at the University of Sheffield showed that if materials coated with oppositely charged polyelectrolytes are brought together in water they stick tightly.

The adhesion is nearly as strong as that of epoxy glue. However, when the bonded materials were immersed in water above a certain acidity level, they came apart. They could be stuck together again by re-immersing them in lower acidity water.

Acidity and alkalinity is measured by pH value, with lower readings denoting higher acidity.

Materials coated with the glue stuck together at a pH above three, and separated when pH fell to below two.

Dr Geoghegan said: “There are several advantages to this mechanism. It is strong, as good as epoxy glue, but reversible in the fact that it can be turned off and still be re-used. It is also water-based, and so environmentally friendly.

“Trying to identify where this will be used is difficult. As scientists we have contributed what you might call the molecular tools of nanotechnology with our adhesive, but it is up to the engineers to decide how to use it.

“Drug delivery is always a possibility because different parts of the body have different pH values. A possibility is that the body’s natural pH could be used with the adhesive to allow drug release.”